low impact development technology : implementation and economics
TRANSCRIPT
Low Impact Development Technology
Implementation and Economics
SPONSORED BY
Low Impact Development Committee of the Urban Water Resources Research Council
of the Environmental and Water Resources Institute of the American Society of Civil Engineers
EDITED BY
Michael L. Clar, P.E., D.WRE Robert G. Traver, P.E., D.WRE Shirley E. Clark, P.E., D.WRE
Shannon Lucas Keith Lichten, P.E.
Michael A. Ports, P.E., D.WRE Aaron Poretsky
Published by the American Society of Civil Engineers
Library of Congress Cataloging-in-Publication Data Low Impact Development Conference (2011 : Philadelphia, Pa.) Low impact development technology : implementation and economics / sponsored by Low Impact Development Committee of the Urban Water Resources Research Council of the Environmental and Water Resources Institute of the American Society of Civil Engineers ; edited by Michael L. Clar, P.E., D.WRE, Robert G. Traver, P.E., D.WRE, Shirley E. Clark, P.E., D.WRE, Shannon Lucas, Keith Lichten, P.E., Michael A. Ports, P.E., D.WRE, Aaron Poretsky. pages cm Papers presented at the 2011 Low Impact Development Conference, held in Philadelphia, Pennsylvania, September 25-18, 2011. Includes bibliographical references and index. ISBN 978-0-7844-1387-6 (paper : alk. paper) -- ISBN 978-0-7844-7896-7 (PDF) 1. Urban runoff--Management--Congresses. 2. Sanitary engineering--Congresses. 3. Sustainable development--Congresses. I. Clar, Michael L. II. American Society of Civil Engineers. Low Impact Development Committee. III. Title. TD657.L69 2015 363.72'84--dc23 2014043591 Published by American Society of Civil Engineers 1801 Alexander Bell Drive Reston, Virginia, 20191-4382 www.asce.org/bookstore | ascelibrary.org Any statements expressed in these materials are those of the individual authors and do not necessarily represent the views of ASCE, which takes no responsibility for any statement made herein. No reference made in this publication to any specific method, product, process, or service constitutes or implies an endorsement, recommendation, or warranty thereof by ASCE. The materials are for general information only and do not represent a standard of ASCE, nor are they intended as a reference in purchase specifications, contracts, regulations, statutes, or any other legal document. ASCE makes no representation or warranty of any kind, whether express or implied, concerning the accuracy, completeness, suitability, or utility of any information, apparatus, product, or process discussed in this publication, and assumes no liability therefor. The information contained in these materials should not be used without first securing competent advice with respect to its suitability for any general or specific application. Anyone utilizing such information assumes all liability arising from such use, including but not limited to infringement of any patent or patents. ASCE and American Society of Civil Engineers—Registered in U.S. Patent and Trademark Office. Photocopies and permissions. Permission to photocopy or reproduce material from ASCE publications can be requested by sending an e-mail to [email protected] or by locating a title in ASCE's Civil Engineering Database (http://cedb.asce.org) or ASCE Library (http://ascelibrary.org) and using the “Permissions” link. Errata: Errata, if any, can be found at http://dx.doi.org/10.1061/9780784413876. Copyright © 2015 by the American Society of Civil Engineers. All Rights Reserved. ISBN 978-0-7844-1387-6 (paper) ISBN 978-0-7844-7896-7 (PDF) Manufactured in the United States of America.
Contents
Introduction ................................................................................................................. 1
LID Implementation Roadblocks
Puget Sound Partnership’s LID Technical Assistance Program: 2009-2011 Update ........................................................................................................ 5 Bruce T. Wulkan
Overcoming Barriers to Implementation of LID Practices .................................. 17 Rod Frederick, R. Fernando Pasquel, and Hunter J. Loftin
A Low Impact Development (LID) Guidance Document and Model Ordinance ...................................................................................................... 26 Steve Trinkaus and Michael Clar
The Farmington River Enhancement Grants: A Tale of Three Towns and the Path to Low Impact Development ........................................................................... 35 Steve Trinkhaus
Beyond the Green Infrastructure: What Do You Do with the Trash and Debris? ................................................................................................................ 46 Hans de Bruijn Sr.
LID Economics
Measuring the Cost-Effectiveness of LID and Conventional Stormwater Management Plans Using Life Cycle Costs and Performance Metrics ............... 54 J. Alex Forasté, Robert Goo, Joel Thrash, and Lisa Hair
Economic and Adaptation Benefits of Low Impact Development ....................... 74 Robert M. Roseen, Todd V. Janeski, Michael Simpson, James H. Houle, Jeff Gunderson, and Thomas P. Ballestero
A Comparison of Maintenance Costs, Labor Demands, and System Performance for LID and Conventional Stormwater Management .................... 93 James J. Houle, Robert M. Roseen, Thomas P. Ballestero, Timothy A. Puls, and James Sherrard
Integrated LID and Green Infrastructure Planning at Rutgers University to Achieve Better Ecological Outcomes at Lower Cost ........................................... 106 Ted Brown, Jennifer Dowdell, Seth Richter, and Larry Porter
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Preface
Low Impact Development (LID) technology has rapidly become the standard for stormwater management in Federal, State and local jurisdictions throughout the United States and in many other countries throughout the world including; Australia, Canada, China, England, New Zealand, and Taiwan. As with many new and emerging technologies there is a learning curve associated with the application of the technology. The Low Impact Development Committee of the Urban Water Resources Research Council (UWRRC) of Environmental and Water Resources Institute (EWRI) of the American Society of Civil Engineers (ASCE) was formed to bridge this learning curve and facilitate the adoption of this new technology. One of the primary tools of the committee has been the sponsorship of a series of national and international conferences on LID technology which present the latest ideas and advances in the technology. One of these conferences was held in Philadelphia, Pennsylvania in September 2011.
The Philadelphia LID conference addressed two of the major areas of uncertainty in LID which include implementation procedures and roadblocks and the economic impacts associated with the implementation of this technology. These two topics are the focus of this publication which presents a number of selected papers from the Philadelphia conference.
Topics covered under the implementation of LID at the local level include:
Regulations & Codes Outreach Activities Planning and Information Exchange Policy Incentives to Encourage LID LID Strategies: Changing Behavior of Individuals & Institutions
LID economics, addresses a wide range of economic issues which include:
Economic Benefits of Individual LID Practices Operations and Maintenance Considerations for LID Practices LID Life Cycle Costs and Performance Metrics.
The Philadelphia LID conference also addressed a wide range of LID design topics and presented a number of case studies of LID applications. These materials are presented in a companion volume, Low Impact Development Technology: Design Methods and Case Studies.
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Acknowledgments
The Philadelphia National LID conference and the proceedings of the conference could not have been possible without the dedicated efforts and leadership of the conference chairs: Dr. Robert Traver, Villanova University; Dr. Bill Hunt North Carolina State University; and Dr. Allen Davis, University of Maryland. In addition the outstanding efforts of Ms. Cathy Smith, Extension Associate of North Carolina State University are hereby acknowledged. Many individuals were responsible for the success of the Conference. Our appreciation and gratitude are extended to the conference partners:
US EPA Environmental & Water Resources Institute LID Center Water Environment Research Foundation Philadelphia Water Department - Office of Watersheds Temple-Villanova Sustainable Stormwater Initiative Temple University - Center for Sustainable Communities Center for Watershed Protection Chesapeake Stormwater Network
Our gratitude is also extended to the authors of the papers presented in this publication for their hard work and valuable contributions in the advancement of Lid technology. We also extend our gratitude to the co-editors who donated their valuable time and intellect editing the technical papers presented in this publication. The co-editors include:
Michael Clar, Ecosite, Inc., Ellicott City, MD Shirley Clark, Penn State University-Harrisburg, PA Shannon Lucas, Brightwater, Inc., Ellicott City, MD Keith Lichten, California Water Boards, Oakland, CA Michael Ports, Ports Engineering, Jacksonville, FL Aaron Poretsky, Geosyntec, Portland, OR Robert Traver, Villanova University, Villanova, PA
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Finally our gratitude is also extended to all the conference co-sponsors both public and private organizations, including:
USEPA 319 National Monitoring Program Contech, Scarborough, ME
http://www.contech-cpi.com/urbangreen Tetra Tech, Inc., Pasadena, CA
http://www.tetratech.com/ Filterra Bioretention Systems, Ashland, VA
http://www.filterra.com/ AbTech Industries, Scottsdale, Arizona
http://www.abtechindustries.com/ CDM, Cambridge, MA
http://www.cdm.com/ AKRF, New York, NY
http://www.akrf.com/ Belgard Commercial, An Oldcastle Company, Atlanta, GA
http://www.oldcastle.com/ Biohabitats, Baltimore, MD
http://www.biohabitats.com/ Greenhorne & O’Mara, Laurel, MD
http://www.g-and-o.com/main.asp Michael Baker Jr., Inc., Philadelphia, PA
http://www.mbakercorp.com/ Ernst Conservation Seeds, Meadville, PA
http://www.ernstseed.com Trans-Pacific Engineering Corporation, Willow Grove, PA
http://www.tpeceng.com
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Introduction Low Impact Development (LID) technology is being increasingly adopted by Federal, State, and local government agencies as the preferred and sustainable approach to stormwater management associated with land development and redevelopment activities. Considering that this technology is only slightly over ten years old (e.g., the first LID Design Manual was published by Prince George’s County, Maryland in 1998), it represents an unusually rapid rate of adoption for a new technology. This rapid adoption is due in part to the realization by local governments that the traditional approaches to stormwater management were not achieving the desired environmental protection goals, as well as the recognition that LID technology is based on ecologically sensitive and sustainable concepts that are essential and necessary to ensure that these environmental protection objectives are achieved. The rapid adoption of LID technology notwithstanding there are two major areas of uncertainty which confront the application of LID technology and which were addressed at the conference. These two topics which are the focus of this publication include LID Implementation Strategies and LID Economics. Issues Associated with the Implementation of LID As any new idea or technology is introduced, it is typical to experience some degree of resistance to its implementation. In the case of LID, which is a permanent change in our land use practices, it represents a paradigm shift in the way that we look at development practices and the handling of stormwater, this pushback can be significant. On the regulatory side of the coin, there are three major areas where this resistance has been encountered and documented.
1) Regulatory Framework 2) LID Technology 3) Education and Training
Regulatory Framework. There are various regulatory requirements which create conflicts between land use agencies with the current approach to site development and stormwater management today. The implementation of a new paradigm like LID can create larger conflicts between these agencies. In many parts of the country, land use decisions are commonly made at the County or Municipal level. In many cases, there are multiple agencies which have input in the final land use decisions and not all of the individual agency goals are aligned which creates these conflicts. In order to implement LID, the various agencies and goals must become more aligned for the greater good of the environment and society.
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In a typical municipality, the following agencies are commonly found:
1) Zoning Commission, 2) Planning Commission, 3) Natural Resource Management Department, 4) Department of Public Works, 5) Building Department, 6) Fire Marshall, 7) Health Department
Each agency or department has a specific programmatic mandate and they have a tendency to work in separate silos which may have conflicting interests. At the present time in many municipalities, the agencies various regulations and rules either prohibit or complicate the implementation of LID. A necessary step to overcoming these issues is to review the regulatory framework and remove the barriers and impediments to LID. LID Technology . LID is a relatively new and rapidly developing technology which triggers numerous questions about this technology, particularly from the community at large. Many end users (homeowners and commercial landlords) and land use agencies are very reluctant to implement LID primarily because of “fear of the unknown”. Some of the most common issues are stated below with approaches to address the issue:
� What is LID and how does it work? � Will it work in the climatic conditions where I live? � Does LID work in difficult soils like clay ? � How do you design and build LID systems? � What are the maintenance requirements? � Who will be responsible if it fails? � Will this be the new “fad” in land use and stormwater management? � How expensive are LID systems?
Education and Training. Low Impact Development (LID) is a relatively new concept in the land development field in many parts of this country. Many municipalities, developers, builders, design engineers and homeowners are not familiar with LID, its strategies, design philosophy and requirements. This unfamiliarity and uncertainty associated with LID can be an obstacle to the
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widespread implementation of LID in many parts of this country. The public education for the implementation of LID must include the environmental, aesthetic and financial benefits that LID can provide.
The regulatory community of land use agency members, professional staff, planners, town engineers and enforcement staff must become knowledgeable about LID. Many concerns about LID have been expressed by regulators, designers and homeowners in many parts of the country. These concerns are summarized in the list below:
1) Fear of liability (engineers, landscape architects, builders, owners, and
regulatory reviewers), 2) Reluctance to try something new, 3) Lack or demonstration projects, 4) Lack of education and training, 5) Public perception,’ 6) Homeowner acceptance, understanding and willingness to maintain
LID systems on their property, 7) Insufficient designer and policymaker familiarity with LID
applications and limitations, 8) Performance and reliability of LID systems, 9) Design of LID systems, 10) Construction specifications for LID systems, 11) Maintenance requirements for LID systems.
The need for education and training of all the stakeholders in the development field cannot be overstated. Without education of the various stakeholders, the implementation of LID will be slow, erratic and uncertain. It is extremely important to educate all the stakeholders including: developers/builders, regulators, designers and homeowners, about Low Impact Development and the many benefits that the implementation of LID will provide for all. Each stakeholder must understand and appreciate the perspective of the other stakeholders. This understanding will facilitate the widespread implementation of Low Impact Development. Many of these issues associated with the implementation of LID are discussed in the papers presented in this publication. LID Economics The implementation of LID can have significant financial advantages over conventional storm water management systems with regard to the actual infrastructure costs. The widespread application of Environmental Site Design Strategies and Flexible/Open Space residential subdivisions will create projects, which are inherently more marketable to the consumer, while providing protection of
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environmentally sensitive lands. By creating projects that protect natural resources, developers will likely find that the path to land use approval is easier and faster. In addition, the maintenance costs of LID treatment systems can be significantly less than for Conventional storm water treatment systems. On the design side of the equation, there may be an increased incremental cost for a civil engineer to design a project that utilizes LID, but the infrastructure cost savings will more than offset the incremental design costs. These concepts are discussed in great detail in the papers provided in this publication. In particular the life cycle approach to economic evaluation is discussed which provides a more technically robust and comprehensive look at economic considerations.
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Puget Sound Partnership’s LID Technical Assistance Program: 2009-2011 Update
Bruce T. Wulkan1
1Senior Policy Advisor, Puget Sound Partnership, 326 East D Street, Tacoma, WA. 98421, Email: [email protected], Phone: (360) 339-4626 Abstract
Since 2001, the Puget Sound Partnership (Partnership), and its predecessor, the Puget Sound Action Team have provided technical assistance on low impact development (LID) to numerous audiences in the Puget Sound region. The intent of the assistance is to help transition the region to the LID approach as the preferred method for developing land and managing stormwater.
During 2001-09, the Partnership, with numerous regional partners, convened the first national conference on LID; held regional workshops; developed educational and technical publications; co-produced the region’s technical guidance manual; and provided technical assistance to help 36 local governments in the region integrate LID into their codes and standards.
This paper provides a brief overview of the technical assistance provided to the region both during this time period (2001-09) and immediately afterwards (during the 2009-11 state biennium). Assistance evolved significantly during this latter time frame due to dramatic changes at the state level regarding LID: LID was rapidly transitioning from a voluntary to a required approach. This paper will briefly describe these changes, and describe how the products and services evolved to meet these changing needs. Introduction
Since 2001, the Puget Sound Partnership (Partnership), and its predecessor, the Puget Sound Action Team have provided technical assistance on low impact development (LID) to numerous key audiences in the Puget Sound region. The intent of the assistance has been to help transition the region to the LID approach as the preferred method for land development and stormwater management.
During this time (2001-09), the Partnership, with numerous regional partners, convened the nation’s first national conference on LID; held regional workshops; developed educational and technical publications; co-produced the region’s technical
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guidance manual; provided direct technical assistance to help 36 local governments in the region integrate LID into their codes and standards; and partnered to provide extensive professional training.
This paper provides an overview of the technical assistance provided to the region immediately following this time period (the 2009-11 state biennium), with an emphasis on products and services, collaborative partnerships, accomplishments, and challenges. For this two-year period, the Partnership, working with regional partners: 1) Assessed 2005-09 LID Local Regulation Assistance efforts; 2) Partnered to provide two rounds of LID professional workshops; 3) Partnered to begin updating the region’s LID technical guidance manual; and 4) Developed a new draft guidebook to help local government staff integrate LID into their codes and standards.
This assistance was provided during, and shaped by, dramatic changes in stormwater management in the Puget Sound region: Due to court rulings and subsequent revisions to federally-mandated permits, LID was transitioning from an encouraged to a required approach. This paper will briefly describe these changes, and how assistance evolved and responded to meet the shifting policy and regulatory landscape. Background
The Puget Sound Partnership (Partnership) was established by the Washington State legislature in 2007 with three primary charges:
• Define a plan (the Action Agenda) that identifies work needed to protect and restore Puget Sound by 2020;
• Establish a system of accountability to achieve results including performance, effectiveness, and the efficient use of funding; and
• Build public awareness and communication to increase support for implementing a long-term strategy (Puget Sound Partnership, 2008).
The Partnership succeeded the Puget Sound Action Team and the Puget
Sound Water Quality Authority, both of which had similar state legislative charges to coordinate efforts related to the protection and recovery of Puget Sound.
Key differences between the Puget Sound Partnership and its predecessors include:
• New goals relating to human health and well-being; • New responsibilities related to salmon recovery, groundwater, and upland
terrestrial species; • New boards: The science-based “Science Panel”; the policy-based
“Ecosystem Coordination Board”; and the decision-making “Leadership Council.”
• New requirement to update the strategies and near-term actions contained in the Action Agenda every two years.
• New responsibilities related to tracking implementation and performance.
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• New 2020 “targets” related to species and food webs, water quality, water quantity, protection and restoration of habitat, human quality of life, and human health (Puget Sound Partnership, 2011).
The Partnership remains part of the U.S. EPA’s National Estuary Program and
remains a non-regulatory agency. Participation in the National Estuary Program ensures ongoing communication and coordination with EPA as well as a steady funding source for planning and implementation. The Partnership’s non-regulatory status allows it to more nimbly address emerging issues and partner with the greater Puget Sound community in an open, non-threatening way.
The Partnership’s planning area (the Puget Sound watershed) is large and diverse, and includes 2,500 miles of shoreline; 14 primary rivers and 10,000 smaller rivers and streams; 127 cities, towns and counties; 15 tribal nations; and 3.5 million people with another 1.7 million projected by 2025. The rich and diverse ecosystem includes 200 fish species, 26 marine mammal species, 3 distinct orca species, and 8 salmonid species. Puget Sound is an economic engine for the state: Annual sales of oysters, clams and mussels tops more than $100 million and the Seattle/Tacoma ports are the second largest in the nation (Puget Sound Partnership, 2011).
2001-09 LID Technical Assistance
The 2000 Puget Sound Water Quality Management Plan, developed by the Partnership’s predecessor, the Puget Sound Water Quality Action Team (Action Team), directed all local governments in the region to revise their regulations to allow and encourage LID (Puget Sound Water Quality Action Team, 2000).
This directive was in response to two primary drivers: First, the negative effects of stormwater runoff on the Sound’s resources, as evidenced by water quality impairments, alteration of salmonid habitat in lowland streams, restrictions in shellfish harvest, and declining aquatic wildlife populations (Puget Sound Water Quality Action Team, 2000). Second, there was growing evidence that conventional stormwater management measures (e.g., ponds, vaults and connected discharges) were failing to fully mitigate for the full range of impacts caused by land conversion and development. This evidence is ably captured in the summary paper, “Forest Cover, Impervious-Surface Area, And The Mitigation Of Stormwater Impacts” (Booth et al, 2007).
Following this directive in the region’s recovery plan, the Action Team undertook a number of projects with key regional partners to first introduce LID to the region, then increase awareness levels, then increase professional competency, and finally, remove regulatory hurdles to implementation. Key activities during 2001-09 include:
• 2001: Convened the first national LID conference; • 2002: Held a series of LID workshops around the region;
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• 2003: Produced Natural Approaches to Stormwater Management, a case study of regional LID projects (Puget Sound Action Team);
• 2004: Produced Reining in the Rain, a case study of one city’s significant cost savings using rain gardens to retrofit a parking lot (Puget Sound Action Team);
• 2005: Co-produced one of the nation’s first LID technical guidance manuals, the LID Technical Guidance Manual for Puget Sound (Puget Sound Action Team and Washington State University Extension, 2005);
• 2005-09: Provided technical assistance to a total of 36 local governments and helped them integrate LID into their land development and stormwater codes, regulations and standards;
• 2007-09: Partnered with Washington State University (WSU) Extension to provide four two-day training workshops on all aspects of LID. Funding for these activities came from EPA National Estuary Program
funding, state agency grants, and sponsorships (in the case of the conference and workshops). To keep costs as low as possible, in-house staff were used extensively in conjunction with volunteer time provided by staff from public agencies and engineering firms. Starting in July 2007, the Washington State Legislature provided a proviso for LID technical assistance in the state budget.
The “LID Technical Assistance Program” contains three related components: 1. LID Local Regulation Assistance 2. LID Technical Guidance 3. LID Professional Training
LID Local Regulation Assistance (2005-09)
LID Local Regulatory Assistance during this time was comprised of free technical assistance to local governments that demonstrated, through a competitive process, strong interest in revising their land development and stormwater management codes, regulations and standards to integrate LID. Proposals were requested of local governments and the highest scoring proposals (selected by a team of internal staff) were selected to receive assistance. Following a competitive process, an engineering firm (AHBL) was selected to provide the assistance. During 2005-09, a total of 36 cities, towns and counties in Puget Sound received this free assistance (Puget Sound Partnership, 2011). The local governments themselves chose whether to allow and encourage LID or require its use. A package of recommendations was delivered, which included rewritten codes in legislative format (strikeout/underline), newly developed codes, new engineering designs and standards, and other information. Local government staff then took the package to their officials for consideration. The full recommendations are extensive and fill large binders; summaries of the assistance are available at: www.psp.wa.gov Follow links to Science and Technical Programs, then Stormwater and LID, then local regulation assistance.
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LID Technical Guidance (2004-09)
LID technical guidance during this time centered largely on the development, distribution and presentation of the 2005 LID Technical Guidance Manual for Puget Sound. The manual contains the technical information needed to adequately site, design, install, and maintain LID techniques in the region. It also contains performance information, a series of appendices, and introductory information for lay audiences. Researched and written by WSU Extension and edited, designed and produced by the Partnership, the manual proved very popular and underwent numerous reprints. The manual can be downloaded at: www.psp.wa.gov. Follow links to Documents, then Agency Documents. In addition, the Partnership funded WSU Extension to research and refine bioretention soil specifications, which improved the region’s confidence in bioretention as an effective treatment tool. LID Professional Training (2007-09)
LID Professional training during this period was largely provided by WSU Extension. WSU Extension, with numerous regional partners, developed curriculum on virtually all aspects of LID: siting, design, installation, maintenance and expected performance. Partnership funding significantly reduced registration fees, cutting fees in half. This resulted in much higher participation, and all classes filled quickly. Classes were two days in length each, and were divided into four topic areas: Site Planning, Soils and Bioretention, Permeable Pavement, and LID Foundations (which included rainwater harvest and vegetated roofs). A total of 1105 participants attended the classes, with many taking all four of the classes. In addition to this training, the University of Washington also offered a certificate program that spanned approximately nine months. This class also covered all key aspects of LID. The Partnership provided a limited number of scholarships to non-profit organizations, schools, and tribes to increase participation of the UW classes.
2009-11 LID Technical Assistance
LID Technical Assistance during the 2009-11 state biennium was significantly different from previous assistance. This was due to dramatic changes at the state level regarding how stormwater runoff should be managed.
In 2007, numerous parties appealed the recently issued Municipal General NPDES (National Pollutant Discharge Elimination System) permits for Western Washington (Washington Department of Ecology, 2011). Appellants raised numerous issues, but perhaps none produced so much discussion – and follow up work – as the appeals related to LID. The permits had required Municipal NPDES Phase I permittees in the region to allow LID and required Phase II permittees to identify barriers to LID implementation. Environmental organizations, however, argued that LID should be required, as LID constituted AKART (All Known And Reasonable Technologies) – a key standard of level of stormwater management effort.
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These permit appeals had actually affected the last round of LID Local Regulation Assistance, delivered in 2009: All four local governments receiving assistance that year – even those not covered by the Municipal NPDES permits – requested that recommendations be tailored so they could require LID in new development projects. This was a marked shift from the previous 32 local governments that had received assistance – those governments were generally more interested in allowing and encouraging LID in new development projects.
Following deliberation, the Pollution Control Hearings Board (Hearings Board) ruled in August 2008 on LID and several other issues under appeal. The Hearings Board ordered the Department of Ecology to modify Section S5.c.5.b of the existing Phase I permit to read as follows:
“The program must require non-structural preventative actions and source reduction approaches, including Low Impact Development Techniques (LID), to minimize the creation of impervious surfaces, and measures to minimize the disturbance of soils and vegetation where feasible.” (Washington State Pollution Control Hearings Board 2008).
The Hearings Board did not define which aspects of LID should be required,
nor did it define where and under what conditions LID should be considered feasible. Those critical determinations would need to be made by the Department of Ecology, as administrator of the permit.
The Hearings Board then ruled on appeals of the Phase II permit in February 2009, also finding that requiring permittees to merely allow LID was not sufficient. Yet the Hearings Board, presumably understanding the differences between the largePhase I permittees and the smaller Phase II permittees, stopped short of similarly requiring LID in the Phase II permits. Instead, the permits should set forth additional requirements during the current permit term, such as identifying barriers to the use of LID; identifying currently available and understood LID practices, identifying non-structural actions and LID techniques to prevent stormwater impacts; establishing goals and metrics to promote and measure LID use; including schedules for LID implementation (Washington State Pollution Control Hearings Board, 2009). These new requirements in the existing permit were intended to prepare Phase II communities for additional LID requirements in future permits.
Following these rulings, the Department of Ecology convened two advisory committees (technical and implementation) during 2009-10 to advise the department on key questions and issues (Washington Department of Ecology, 2011). This author was a member of both advisory committees and participated in numerous, lively discussions regarding:
• Which LID techniques should be required? • Should requirements extend to setting limits on preserving native vegetation
and limiting impervious surface cover on site?
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• Under which conditions should certain LID techniques be considered infeasible?
• For which types of new development should a new LID flow control standard be required?
Rather than modifying the existing municipal permits to meet these rulings, the Department of Ecology chose instead to use advice from the two advisory committees to add LID requirements to updated permits scheduled to be released in July 2012. The department’s LID requirements in the drafts of the Municipal Phase I and II permits for western Washington were released on October 19, 2011 (Washington Department of Ecology, 2011).
The Partnership’s LID Technical Assistance Program adjusted to meet this transition from LID being allowed and encouraged to require. Similar to the 2005-09 time period, assistance provided during this time can be divided into three primary areas: LID Local Regulation Assistance; LID Technical Guidance; and LID Professional Training. LID Local Regulation Assistance (2009-11)
As stated previously, the Partnership provided detailed recommendations to 36 local governments in the basin regarding how to integrate LID into their codes and standards. Before embarking on additional assistance, the Partnership felt it was very important to assess the effectiveness of assistance provided to date.
In Spring 2010, the Partnership used a third party (an engineering firm not associated with the assistance provided) to survey staff from the 36 local governments to:
• Document each local government’s progress in adopting recommendations; • Identify obstacles to greater adoption of the recommendations and solutions to
overcome these obstacles; • Inventory each local government’s progress toward implementing LID apart
from regulatory changes undertaken; • Identify obstacles to further implementation of LID and solutions to overcome
these obstacles; and • Solicit recommendations on how to increase LID implementation in the region.
(CH2M Hill and ESA Adolfson, 2010)
Survey results are interesting, and provide numerous insights. For instance, local governments have made significant progress through means other than regulatory changes. Progress has been through their own shared vision of LID implementation. Non-regulatory organizations, such as environmental groups and building associations, are key partners. Local governments strongly want to share accomplishments and lessons learned. Local governments anticipate new LID requirements in the municipal permits. During slower economic times, “required” activities are fulfilled while “encouraged” activities are more easily delayed. Most of
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the local governments had not adopted all the recommendations provided, yet they found the assistance very helpful. Finally, about half (17) of the governments had adopted at least some of the recommendations.
Based on the results of this survey, and the extensive recommendations already provided, the Partnership felt there were sufficient examples and models of codes and standards for local government staff in the region to draw upon. In addition, the new municipal NPDES permits for the region would soon require all permittees to revise their codes and standards to require LID where feasible. This included a total of 81 cities, towns and counties, the vast majority of which were smaller Phase II permittees that lacked the staff capacity of the larger Phase I permittees.
Following discussions with the Department of Ecology, WSU Extension, and municipal permittees, the Partnership decided that LID Local Regulation Assistance provided during the 2009-11 state biennium would take the form of a new, step-by-step guidebook for local government staff. The guidebook would be targeted to local government staff, and would walk staff through the entire process of reviewing and revising existing codes and standards, developing new ones, and presenting changes to their elected officials. AHBL was selected to develop this guidebook, with a small core team and an advisory group.
The guidebook, Integrating LID into Local Codes: A Guidebook for Local Governments (Puget Sound Partnership, 2011), outlines:
• Essential department staff to include on an LID code revision team; • Steps to quickly bring team members up to a common understanding of LID; • Topics and issues to identify and address; • Where to locate the topics and issues in local codes and standards; • How best to amend existing and develop new codes and standards; and • How to package and forward the revisions to local officials for consideration
and adoption.
At the time of this writing, the guidebook was in final draft form (November 2011 final draft version); the Partnership plans to finalize it in July 2012. The guidebook is referenced as primary guidance for Municipal Phase I and II permittees in the draft permits for western Washington (Washington Department of Ecology, 2011). LID Technical Guidance (2009-11)
The LID Technical Guidance Manual, as stated previously, was released in 2005. Since then, regional, national and international professionals had gained a tremendous amount of knowledge and experience regarding LID. The Partnership, WSU Extension, and the Department of Ecology agreed a new edition of the manual was needed.
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With these offices forming a core team, it was decided that WSU Extension should again research and write the manual, with significant help from a technical advisory team and other regional topical experts. The Partnership would again serve as funder (using state funds), editor, designer/layout, and oversee printing and distribution. As the Department of Ecology was updating their technical manual in conjunction with the updated municipal stormwater permits, it was critical to again ensure that the LID guidance manual was consistent with the department’s regional manual.
Consistency included design guidelines, instructions for modeling LID techniques, and maintenance recommendations. This “two-manual” system had worked well during 2005-10, with the LID guidance manual covering areas such as site assessment, site planning (including clustering), protection of native vegetation, and coverage of all LID techniques. The department’s regional manual included all conventional best management practices, minimum requirements for all development, and other areas more closely associated with NPDES permits.
The LID guidance manual’s technical advisory committee, composed of regional professionals from local governments, private engineering firms, building associations, and state offices began meeting in June 2010. A public review draft was released in January 2012. Similar to the 2005 manual, the new edition contains:
• Introductory information on the effects of urbanization, site hydrology and the need for LID;
• Site assessment for different size projects; • Site planning and layout for different size and types of projects; • Vegetation and soil protection and revegetation; • Precision site preparation and construction, inspection and sequencing; • Integrated management practices, including design, construction,
maintenance and expected performance; • Instructions for how to model practices using the state’s stormwater models; • Appendices: Bioretention plant list, performance, and recommended soil
mixes; Maintenance of practices; Street tree list; Compost specifications; and Permeable pavement performance (Puget Sound Partnership, 2012).
The LID Technical Guidance Manual for Puget Sound, 2012 Edition is
scheduled to be released in summer 2012. It will complement the Department of Ecology’s manual for western Washington and provide municipal NPDES permittees, other permittees, and non-permitted local governments the necessary information to appropriately site, design, construct, and maintain LID practices in the Puget Sound region. Unlike the previous version, this edition will only be available for download, as state budget cuts prevent printing copies. LID Professional Training (2009-11)
LID professional training during this period continued with several key changes. First, WSU Extension used funding from the Partnership to offer all training
LID: IMPLEMENTATION AND ECONOMICS 13
workshops at their Puyallup, Washington campus, which was in the process of becoming a significant regional (and national) LID research facility under the newly created “Washington Stormwater Center.” WSU had received a state grant from the Department of Ecology to retrofit portions of the campus using LID techniques. WSU chose to retrofit a 100-space parking lot with porous asphalt and pervious concrete, and construct 20 “mesocosms” to test and research a variety of bioretention soil mixes. Monitoring was initiated for both flow control and water quality treatment (Washington Stormwater Center, 2012). Holding the workshops on the campus allowed instructors and students to tour the research facility and experience two common LID techniques as well as LID monitoring.
A second difference was that the WSU Extension classes were intentionally kept small (maximum 65 per class) to ensure a high-quality learning experience for both students and instructors. Instructors were regional experts drawn from local governments, engineering and landscape architecture firms, industry, and state agencies. A set of four two-day workshops covered all aspects of LID similar to previous years. A set of workshops was offered each year. A total of 260 professionals were trained during 2009-11; the classes sold out early and waiting lists were established. Certificates were also offered for those who attended all four 2-day workshops and passed a series of tests demonstrating competence. For the 2010-11 series of workshops, 56 professionals received certificates (WSU Extension, 2011).
In addition, the University of Washington (UW) also offered a professional LID certificate program. The program was offered over the course of nine months. Curriculum was divided into three main areas: The foundations of LID covering the legal framework, site assessment and the basics of LID; Siting and design of LID practices; and Implementation in the field, which included inspection and maintenance. Instructors were drawn from engineering firms; guest instructors from various offices were also brought in. Twenty-nine students received certificates under this program in 2009-10; another 19 received certificates during 2010-11 (Carlson, 2012). The UW plans to transition this training to an on-line course. Conclusions
Since 2001, the Puget Sound Partnership and its predecessor, the Puget Sound Action Team have provided technical assistance on LID to numerous audiences in the Puget Sound region. The intent of the assistance has been to help transition the region so that the LID approach becomes the preferred method for land development and stormwater management.
During 2001-09, the Partnership, with numerous regional partners, introduced the region to the LID approach and worked to significantly increase awareness, knowledge level, and competency regarding the approach and individual techniques. During 2009-11, court rulings led to LID transitioning rapidly in the region from an approach that is encouraged to one that is required, where feasible. The Partnership
LID: IMPLEMENTATION AND ECONOMICS 14
and its many partners adjusted technical assistance to meet this shifting policy and regulatory landscape.
Today, LID is rapidly moving forward in the Puget Sound region and one can point to many successes: Projects in every county; increasing knowledge base of professionals; numerous non-profit organizations promoting LID; regional guidance manuals with agreed-upon methods of modeling techniques; high-quality, inexpensive training opportunities; and an impressive regional research facility. When the region’s municipal NPDES stormwater permits become effective, the use of certain LID techniques, particularly bioretention and permeable pavement, should increase significantly.
Yet challenges remain: The economic downturn and loss of jobs makes this a tough time to introduce new initiatives. Portions of the region are dominated by till soils, making some professionals reluctant to use LID techniques. Adding LID requirements to federal NPDES permits is difficult, and new permit requirements are often resisted. Additional, more focused training is needed, particularly for LID project review, verification, and inspection and maintenance. Ensuring regular maintenance occurs on private property must still be addressed. Time is needed for local staff to revise their codes and standards to require LID. There remains continuing tension between how best to protect precious native vegetation & minimize impervious surface cover while still respecting property rights.
The Partnership will keep working with regional partners to improve stormwater management so that Puget Sound is protected and restored over time. Stormwater has been discussed as a key initiative to focus on in the next two years. The Action Agenda is being updated in 2012, and stormwater management remains a priority. References Booth, D.B., Hartley, D., and Jackson, R., 2002. Forest cover, Impervious-Surface
Area, And the Mitigation Of Stormwater Impacts, Journal of the American Water Resources Association, Volume 38, Issue 3, pp. 835-845, June 2002.
Carlson, W., 2012, personal communication. CH2M Hill and ESA Adolfson, 2010. Survey of Local Governments that Participated
in the 2005-2009 LID Local Regulation Assistance Project, prepared for the Puget Sound Partnership, April 2010.
Puget Sound Action Team, 2003. Natural Approaches to Stormwater Management, March, 2003.
Puget Sound Action Team, 2004. Reining in the Rain: A case study of the City of Bellingham’s use of rain gardens to manage stormwater, March 2004.
Puget Sound Action Team and Washington State University Extension, 2005. Low Impact Development Technical Guidance Manual for Puget Sound, 2005.
Puget Sound Partnership, 2008. Action Agenda, December 2008.
LID: IMPLEMENTATION AND ECONOMICS 15
Puget Sound Partnership, 2011. Integrating LID into Local Codes: A Guidebook for Local Governments, Puget Sound Partnership, Final draft, November 2011.
Puget Sound Partnership, 2012. Web site on Puget Sound 2020 recovery targets: http://www.psp.wa.gov/action_agenda_2011_recovery_targets.php
Puget Sound Partnership, 2012. Web site on Puget Sound facts: http://www.psparchives.com/puget_sound/psfacts.htm
Puget Sound Partnership, 2012. Web site on 2005-09 LID local regulation assistance: http://www.psparchives.com/our_work/stormwater/lid/lid_regs.htm Puget Sound Partnership, 2012. Web site on LID technical guidance manual:
http://www.psp.wa.gov/LID_manual.php Puget Sound Water Quality Action Team, 2000. 2000 Puget Sound Update: Seventh
Report of the Puget Sound Ambient Monitoring Program. Puget Sound Water Quality Action Team, March 2000.
Puget Sound Water Quality Action Team, 2000. Puget Sound Water Quality Management Plan, 2000.
Washington Department of Ecology, 2012. Web site on appeals to the municipal permits: http://www.ecy.wa.gov/programs/wq/stormwater/municipal/appeals.html
Washington Department of Ecology, 2012. Web site on the LID advisory committees: http://www.ecy.wa.gov/programs/wq/stormwater/municipal/lidTECHadvisory.html
Washington Department of Ecology, 2012. Web site on the municipal NPDES general stormwater permits: http://www.ecy.wa.gov/programs/wq/stormwater/municipal/2012draftMUNIpermits.html
Washington State Pollution Control Hearings Board, 2008. Appeals of Phase I Municipal Stormwater Permit, PCHB Nos. 07-021, 026, 027, 028, 029, 030 & 037, August 7, 2008.
Washington State Pollution Control Hearings Board, 2009. Findings of Fact, Conclusions of Law, and Order, Phase II Municipal Stormwater Permit, PCHB Nos. 07-022, 07-023, February 2, 2009.
Washington State University Extension, 2011. Low Impact Development Technical Workshop Series, Final Report: 2011 Workshops. Prepared by Curtis Hinman, August 23, 2011.
Washington Stormwater Center, 2012. Web site on the WSU Puyallup LID Research Program: http://www.wastormwatercenter.org/low-impact/
LID: IMPLEMENTATION AND ECONOMICS 16
Overcoming Barriers to Implementation of LID Practices
Rod Frederick, P.E., D.WRE, F.ASCE1, R. Fernando Pasquel2, Hunter J. Loftin, P.E.3 1Environmental Engineer, Michael Baker, Jr., Inc., [email protected] 2Vice President, Michael Baker Jr., Inc., [email protected] 3Senior Project Manager, Michael Baker Jr., Inc., [email protected] Abstract
Planners and engineers face many barriers when implementing green infrastructure and Low Impact Development (LID) practices. Some of these barriers are physical and require regulations and/or specialized designs to overcome, while other barriers are caused by perceptions and can be removed through education, outreach, and coordination. Four of the most common barriers are the misperception of how LID works, cost, maintenance, and delayed permit approval.
This paper describes these barriers to the implementation of green
infrastructure/LID practices and provides approaches to overcome them. The approaches are based on lessons learned while implementing LID practices in municipal projects and military facilities. Practitioners need to continue to share lessons they have learned, to facilitate future implementation and demonstrate the success of green infrastructure and LID practices. Understanding LID Practices – How They Work Under Difficult Conditions
LID is the use of various structural and nonstructural practices to manage
stormwater runoff as close to the source as practical. These practices typically consist of treating runoff on the order of 5 acres or less and deliver, if properly designed, stormwater runoff from a site that resembles predevelopment hydrology and water quality. A series of practices working as a “treatment train” or system are typically employed.
One of the barriers for implementation is the thought that LID consists
entirely of filtering and infiltrating stormwater through vegetation and highly permeable soils. Common misperceptions are that LID will not work at sites with poorly draining soils because onsite infiltration is impractical, that it will not work in cold weather because of freezing, and that hot or arid climates cannot sustain the vegetation that will treat stormwater. On the contrary, areas with all of these conditions can benefit from LID practices. New and improved technologies and materials, as well as native vegetation, have been consistently used to demonstrate
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that LID works and is attaining greater implementation in diverse and extreme environments.
The types of practices that can achieve LID are presented below, along with
examples of successful applications in diverse and extreme environments. Cold Climates
This barrier to placing LID practices in areas with continued temperatures
below freezing and with deep frost lines is real, although it is periodic in nature and has to be considered in balance with benefits of LID practices when thawing occurs and during periods when temperatures are above freezing. LID practices such as bioretention, permeable paving, and green roofs have been designed in cold weather climates to function effectively with proper maintenance.
The Center for Watershed Protection report Stormwater BMP Design
Supplement for Cold Climates, (1997) provides useful information on the performance of stormwater BMPs in cold climates and modifications to make them more effective. This report identifies potential problems which include increased runoff and pollutant concentrations due to spring snowmelt, and limited infiltration in frozen soils
Design considerations that can overcome the barriers associated with cold
climates include ensuring good drainage in underlying soils, using sandy course media, and providing larger surface areas for extra surface storage in bioretention cells. Also, plants that can withstand cold weather and salt should be selected (if salt is used for deicing). Bottoms of unlined infiltration LID practices should be at least 2 feet above the seasonal high water table. Permeable paving has been used in cold climates including Sweden, the City of Toronto, Penn State University, Villanova University, and Walden Pond, Mass. Proper maintenance is essential to make sure the pavement drains prior to the cold weather season. In addition to using sandy course media and ensuring well drained underlying soils, deicing operations must avoid application of sand and snow plows should be advised to raise their plow blades to avoid scraping the pavement surface.
Drinking water aquifers underlying LID infiltration devices in cold climates
may also require special considerations such as alternative deicers. Green roofs will require plants that can withstand cold conditions. Snowmelt
and rainfall may drain without infiltrating over frozen surfaces initially, but as warming continues the green roof should begin to infiltrate and drain as designed.
Arid Climates Real barriers to implementation of LID practices in arid climates include
water rights, sustainable plants, and rainfall patterns during short rainy seasons. The use of LID practices may not be allowed where water rights regulations require that
LID: IMPLEMENTATION AND ECONOMICS 18
rainfall must be released to drainage systems. There are many plants that are appropriate for arid areas. The City of Austin, Texas has a “Grow Green” web page which contains plants appropriate for both the bottoms and sides of rain gardens. Plantings are available for green roofs in arid areas from University Extension Services.
In extreme drought conditions, irrigation may be necessary. Rainfall that
occurs during only a short period in large amounts can overwhelm LID practices, resulting in bypass of a significant part of the runoff. However, the first flush of the initial rainfall will likely contain a large portion of the pollutant loads. Therefore, rain gardens can provide water quality benefits. LID practices that provide detention, infiltration, and evapotranspiration can help to reduce peak flows and runoff quantity. Tight/Poorly Drained/Clay Soils
One of the best-known features of LID is the infiltration of stormwater into
underlying soils. This infiltration allows for the balancing of pre- and post-development hydrology to meet the requirements of stormwater permit authorities and regulations. Poorly drained soils containing clays and other occlusions in the soil mantle can cause real barriers to the use of LID practices to meet runoff reduction or hydrologic requirements. These barriers can be partially overcome by careful site inspections and creative designs.
Site inspections can include percolation tests or borings to determine if any
soils on the site can provide infiltration. LID infiltration practices can be used in areas with tight, poorly drained, and clay soils if the site planning and design steps are properly sequenced. Some counties and cities are starting to require an evaluation for LID practices before traditional stormwater management practices are designed for a site. Also, inspections can reveal the presence of soils beneath an occlusion layer that can be reached by “punching” through the layer to receive the discharge created by LID practices. In either case, the cost of additional grading or an injection well must be considered. Previous studies of the site and surrounding areas can be used to determine feasibility before expending funds on a soils study.
LID designs can partially overcome the challenges of tight soils by taking advantage of underlying soils that infiltrate as little as 1 inch per hour, and by using two other features of LID practices (i.e., pollutant removal mechanisms and hydrologic modifications) to enable evapotranspiration and water detention/retention. Additionally, the use of underdrains can take advantage of the filtering capability of some LID practices even in poorly draining native soils. For example, bioretention/rain gardens and permeable paving are typically designed by excavating down 3 to 6 feet to form a bowl or rectangular pit, which is then filled with larger crushed stone at the bottom and various courses of media leading up to plantings or permeable paving. These practices can be used to filter stormwater and the excess water that does not infiltrate into the native soil below the crushed stone can be conveyed by underdrains to a nearby outfall or storm sewer system.
LID: IMPLEMENTATION AND ECONOMICS 19
Bioretention Cells/Rain Gardens The creation of rain gardens is an effective practice for the detention and
retention of runoff. Rain gardens can provide an area for ponding up to 1 foot of water across the surface area of the cell, allowing evapotranspiration until the cell drains. Maximizing the surface area of ponding can increase the total volume of runoff that will be reduced and detained by the bioretention cell. The deeper the cell, the more runoff can be detained; this gives the runoff the opportunity to infiltrate, even if the hydraulic conductivity of the saturated soil (Ksat) is 1 inch per hour or less.
Depth considerations are typically controlled by cost. Underdrains can be
effectively used to provide a reliable discharge, which ensures drainage between storms, but they have the potential to short-circuit infiltration. Underdrains are necessary for tight underlying soils, because these marginal soils are more susceptible to clogging. However, underdrains can be elevated in a bioretention cell or upturned at the low end to allow a greater volume of water to infiltrate between storm events.
A study by the U.S. Geological Survey found that prairie grass in a rain
garden in clay soils captured 100 percent of the runoff over 5 years at a water balance of 20-percent evapotranspiration and 80-percent groundwater recharge. Turf grass in clay soils achieved a capture rate greater than 90 percent (Evaluation of Turf Grass and Prairie –Vegetated Rain Gardens in a Clay and Sand Soil, Madison, Wisconsin, Water Years 2004-08. Scientific Investigation Report, 2010-5077). As well as enabling evapotranspiration, the deep root system of the prairie grass provided the additional benefit of penetrating the clay soils.
When pollutant reduction is a requirement, the amount and type of the media
with the contact time of the runoff within the cell become the prime considerations. These considerations can be incorporated into the design of a bioretention cell, regardless of the tightness of the soils. The only loss of treatment in a tight-soil environment, when compared to one of permeable soils, is the amount of pollutants entrained in the recharge. The challenge is to adjust the depth to be most cost-effective based on the pollutants to be removed. For example, if temperature is to be reduced, the depth should be greater. If oils and bacteria are the pollutants of concern, a shallower depth and greater surface area would provide better results. Permeable Paving
Good practice for permeable paving in an area of tight soils requires the use of
an impervious liner at the bottom of the excavation and an underdrain system that will prevent ponding. Therefore, permeable paving in tight soils will be more costly than in sandy soils (Ksat>2 in/hr) and will reduce peak flows through the detention of runoff between storm events, but it will not provide a significant reduction of the runoff volume. Detention can still be an important consideration, especially in cities with Combined Sewer Overflows (CSOs). The use of chambers, crushed rock, stone,
LID: IMPLEMENTATION AND ECONOMICS 20
or pipes under permeable parking lot paving can provide the detention of large amounts of runoff.
Pollutant reduction will be significantly reduced when chambers or pipes are
used to store runoff, because the processes of adsorption and ion exchange are minimized without fill media. Pollution reduction is achieved in the gravel and stone courses under the permeable paving. The media type and contact time considerations are similar to those for bioretention. However, permeable paving will have loadings not present in bioretention cells, requiring the underlying soil and gravel to have extra strength; this may preclude the use of some media. Also, if pollutants such as bacteria and oils are present, which are commonly reduced on the surface, permeable paving may not provide the same level of pollutant removal as bioretention cells. Costs of LID Practices – Information that Facilitates Implementation
Cost is a major consideration in all engineering designs. Property owners
requiring stormwater management may believe that LID practices create extra costs for a construction project. This perception represents a barrier that can be overcome by proper information from the community and design professionals. LID practices have been shown to reduce the overall construction cost, because they can reduce the amount of paving, curbs, and gutters, thereby eliminating some of the material costs.
LID practices, if applied systematically at the subdivision or small watershed
levels, can reduce the size and cost of flood risk management practices, because they reduce runoff through detention/retention, infiltration, and evapotranspiration. However, LID practices may also increase costs due to expensive plantings and media, underdrains and connections to stormwater systems, and the cost of land where real estate is at a premium. Proper design can minimize these costs.
One way to overcome the perception of cost as a barrier is to provide a
comparison of the cost of stormwater management using conventional control practices with that of using LID practices. On a single-site basis, this is an engineering comparison of cost alternatives. An evaluation of similar sites, one with LID practices and one with conventional practices, is known as a paired study of alternatives; this type of evaluation often includes costs as well as other comparisons.
The EPA report Reducing Stormwater Costs through Low Impact
Development (LID) Strategies and Practices, EPA 841-F-07-006, December 2007, compares the projected and known costs of LID practices with those of conventional approaches to stormwater management. Seventeen case studies nationwide demonstrated that LID practices reduced costs and improved the environmental performance of stormwater management when compared to conventional control practices. These studies did not monetize the environmental benefits, expanded recreational opportunities, or increased property values and increased marketing potential due to the proximity to green space created by LID practices. Also not included were cost reductions associated with reducing the amount of CSOs. This
LID: IMPLEMENTATION AND ECONOMICS 21
EPA report could help inform owners that LID practices can be fiscally and environmentally beneficial.
The LID practice with the greatest capital cost, compared with its
conventional alternative, is a green roof. A life-cycle study by the City of Portland compared the performance of a green roof to that of a traditional roof on a new five-story office building with a 40,000-square-foot roof over a 40-year period (Cost-Benefit Evaluation of Ecoroofs, Low Impact Development, Low Impact Development 2008, ASCE). The economic impacts that were considered included capital and the operations and maintenance (O&M) costs of stormwater management, energy consumption, building construction and its O&M costs, amenity values, impacts on climate (including carbon reduction), and habitat values. Although a green roof is more expensive initially, it has an expected life of over 50 years, as opposed to the 20- to 30-year lifespan of a conventional roof. The replacement cost alone for the conventional roof makes the cost of the green roof less over a 40-year period. Other monetized benefits resulted in even greater savings.
Limited budgets at the local, state, and federal levels also impact the
application of green infrastructure and LID. Alternative funding sources are needed to facilitate LID implementation. Having a reliable funding source can help to ensure that almost all barriers to LID practices in stormwater management are overcome.
One alternative that has proven to provide a reliable funding source for
stormwater programs is the creation of a stormwater utility. The development of stormwater utilities can facilitate the engagement of stakeholders at the local level which, in turn, can create a better understanding of the stormwater program, including the need for green infrastructure and LID. Once a stormwater utility is established, the community will also have reliable funding for the inspection and maintenance of LID practices. Maintenance – All Stormwater Infrastructure Requires Maintenance
Stormwater practices that are not maintained are likely to fail. This statement
is true for both LID and conventional control practices. Personnel who review plans and permit applications that include LID are also aware that maintenance is required. Because many LID practices are distributed throughout a site, their maintenance can be more expensive and difficult than for conventional practices, typically located in only a few places. Many municipalities see maintenance concerns as a barrier for full implementation of LID at the local level.
Although one may argue that the failure of a few of many smaller practices
has less of an impact on the overall performance of a stormwater management system than the failure of one large structural practice, it is good engineering practice to address the maintenance of all facilities, regardless of size and type. It is important to think of all stormwater infrastructure, including LID, as similar to roads and
LID: IMPLEMENTATION AND ECONOMICS 22
water/wastewater systems, which require regular and well-funded maintenance. Maintenance will be required over the lifecycle of LID practices.
Some states require maintenance through the implementation of the National
Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System Permit Program. Maintenance options for stormwater practices, including LID, can be included in this regulation directly or by reference to a local Design or Public Facilities Manual. San Diego County has a Stormwater Management Plan that includes options for required maintenance, depending on the type of stormwater practice proposed ((http://www.sdcounty.ca.gov/dpw/floodcontrol/drainage.html) Regulatory manuals that include the Drainage Design Manual and Standard Urban Stormwater Mitigation Plan). These options include:
• County Maintenance; • Flood Control District, Conservation District, or State/Federal Agency
with a source of funding; • Subsequent Owners (a backup agreement is required with developers); • A County Service Area or Assessment District (Stormwater Utility); • Lease Agreement (County holds title leased to another party for
maintenance); and • Conditional Use Permits that include maintenance.
Many municipalities transfer maintenance responsibilities to homeowners
associations (HOAs) once the development project is completed. The requirement to maintain rain gardens on private property can be added to the deed for the property, to be transferred when the property is sold to subsequent owners. There are concerns with having HOAs or private property owners maintain stormwater infrastructure, because their mission is typically not as focused on stormwater as that of a municipality.
Some municipalities are currently evaluating the implementation of LID
practices only within easements and street right-of-ways. This approach will facilitate future access for maintenance activities and will make it clear that stormwater is a utility operation and that maintenance is required, just as with any other type of municipal infrastructure. The typical municipal maintenance crew will need different skill sets to accommodate the maintenance requirements of LID practices. For example, the crew will need to include landscaping knowledge to ensure the selection and long-term maintenance of proper plants.
Regardless of the type of maintenance option chosen, inspection and an
enforceable mechanism (e.g., maintenance agreements) are recommended to ensure proper maintenance. Therefore, the strongest options are a stormwater utility, county/city maintenance (preferably with ownership of the practice), and a district or agency with dedicated funding.
LID: IMPLEMENTATION AND ECONOMICS 23
Delayed Permit Approval – Good Standards Facilitate Timely Approvals This barrier is identified as a real problem by many developers and
contractors who become reluctant to propose LID practices for stormwater management because permit authorities take longer to approve their landscaping and building permits. This barrier can be overcome by better communication and coordination between multiple agencies and between agencies and the professionals who prepare permit applications. Good, clear standards that have the support of local government and environmental and development organizations typically facilitate timely approvals and provide a predictable review process. Actions that increase awareness and better communication include regulations, policy decisions, and education and outreach, including demonstration projects.
One demonstration project that increased awareness of LID in stormwater
management was the Land/Water Sustainability Forum’s Low Impact Development Competition in Houston, Texas. Houston’s consciousness-raising project resulted in hundreds of developers, civil engineers, architects, landscape architects, and others, including permit personnel, thinking differently about LID and stormwater. Houston decided that a competition to develop the best LID project(s) would be a great way to publicize the issue and increase the comfort of professionals to propose LID projects to their clients. They expressed their goal as follows: "Our goal in this competition is to dramatically accelerate the adoption, adaptation and implementation of Low Impact Development and other sustainable development practices in the Houston area." Information on this approach can be found on the following website: http://www.houstonlwsforum.org/designCompetition/program.html#Judging.
There are many other case studies and policies in cities that are leading the
way in implementing LID as part of green infrastructure for stormwater management. These include demonstration projects, street retrofits, capital projects, local code review, education and outreach, stormwater regulations, and incentives to implement LID (Rain Gardens and Green Streets: The Future of Municipal Stormwater Management in the U.S., Abby Hall, USEPA, Low Impact Development 2008, ASCE). Many cities have created stormwater utilities. Implementing these utilities involves a public process that affects all stakeholders within a municipality, as well as education and outreach. This process helps to improve communication and the speed of permit approvals involving LID.
A community process that involved all stakeholders in Tolland, Connecticut
resulted in the adoption of LID regulations. The involvement and education of design professionals, permit authorities, commissioners, and residents resulted in a regulation that precludes delays in permit approvals (Ahead of the Curve-Tolland, Connecticut Adopts Low Impact Development Regulations, Low Impact Development, 2008, ASCE).
Some of the latest stormwater regulatory requirements involve infiltrating
stormwater to the maximum extent possible, which stimulates the use of LID
LID: IMPLEMENTATION AND ECONOMICS 24
practices (e.g., in New Jersey and Anne Arundel County, Maryland). Some regulations specify that LID practices be considered or used in stormwater management (Contra Costa, California).
The barriers discussed in this paper, although real, can be overcome through
improved communication of the benefits of LID, good design, and sharing the lessons learned during the implementation of the practices. References Center for Watershed Protection. (1997). Stormwater BMP Design Supplement for
Cold Climates. City of Austin, Texas. Grow Green Web Page.
(http//www.austintexas.gov/department/grow-green). Accessed August 13, 2012.
County of San Diego. (2008) Standard Urban Storm Water Mitigation Plan For Land Development and Public Improvement Projects Chapter 5, Maintenance Requirements for Treatment BMPs. Updated 2011 Version: http://www.sdcounty.ca.gov/dpw/watersheds/susmp/susmppdf/susmp_manual_2011.pdf. Accessed August 13, 2012.
Hall, Abby. (2008). Rain Gardens and Green Streets: The Future of Municipal Stormwater Management in the U.S. Low Impact Development Conference 2008, ASCE.
Houston, Texas Land/Water Sustainability Forum. (2010). Low Impact Development Competition. http://www.houstonlwsforum.org/. Accessed August13, 2012
MacMullan, Ed; Reich, Sarah; Puttman, Tom; and Rodgers, Kelly. (2008). Cost-Benefit Evaluation of Ecoroofs. Low Impact Development Conference 2008, ASCE. Madison, Wisconsin. (2010). Evaluation of Turf Grass and Prairie –Vegetated Rain Gardens in a Clay and Sand Soil. Water Years 2004-2008. Scientific Investigation Report 2010-5077. http://pubs.usgs.gov/sir/2010/5077/. Accessed August 13, 2012.
Trinkaus, Steven D. (2008). Ahead of the Curve-Tolland, Connecticut Adopts Low Impact Development Regulations. Low Impact Development Conference 2008, ASCE.
United States Environmental Protection Agency (USEPA). (2007). Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices.
LID: IMPLEMENTATION AND ECONOMICS 25
A Low Impact Development (LID) Guidance Document and Model Ordinance
Steve Trinkaus1 and Michael Clar2
1 Trinkaus Engineering, Southbury, CT, 06488 PH (203) 264-4558, Fax (203) 264-4559; Email: [email protected] 2 Ecosite, Inc., Ellicot City, MD, 21042, PH (410) 804-8000; Fax: 410-730-5464; Email: [email protected]; Abstract
This paper describes the development of a Low Impact Development (LID) Model Ordinance and Guidance documents developed to assist communities which are in the process of adopting LID technology to develop and ordinance that helps them to overcome many of the traditional impediments to the application of this technology.
Many communities throughout the US are interested in implementing LID technology because it offers a sustainable “green” approach to site design and stormwater management. However, in many instance they are faced with a patchwork of local codes (zoning, subdivision, inland wetland regulations, board of health regulations, and safety regulations (Fire Marshall, Department of Transportations, State Environmental Protection Departments)) which may provide overlapping and sometime conflicting regulations which may create impediments to the implementation of LID technology.
The model LID ordinance and guidance documents are being developed as a resource document which accomplishes the following objectives: 1) first, identify the elements of a model LID ordinance and 2) identify the potential impediments to the implementation of LID technology and offers some approaches to address these issues. Defining the Document
As the movement to implement LID grows across the country, many communities and state agencies wrestle with how to incorporate LID into practical land use regulations. There are many different approaches that are being tired to incorporate LID in the land development practices, but there is difference in consistency between all of these approaches.
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At the 2009 World Environmental and Water Resources Congress in Kansas City, MO, there was a discussion between the authors of this paper about the creation of a document that would provide an effective road map to assist communities to implement LID. This document is to be called “Low Impact Development (LID) Guidance Document and Model Ordinance”. It is being developed by the LID Model Ordinance Task Committee, LID Standing Committee under the Urban Water Resources Research Council of the Environmental and Water Resources Institute (EWRI) of American Society of Civil Engineers (ASCE).
It is the goal of the team to prepare a document which leads to the widespread
and locally effective LID codes and rules in this country and perhaps in other nations dealing with the adverse impacts of development and stormwater on our environment. Literature Collection and Review
In developing this guidance document the authors needed to understand the approach to adopt LID that was being used in parts of this country. The authors reviewed existing LID regulations developed in Connecticut, Massachusetts, Rhode Island, the Puget Sound region to name a few. These regulations covered the many possible levels of LID rules, from statewide to county to individual towns. The literature review also provided insights into how the LID regulations were promoted to all the various stakeholders in order to facilitate the adoption. While research was initially focused on existing adopted LID ordinances and regulations, it was expanded to include the results of studies that discussed the environmental benefits and economic benefits of application of LID.
The Guidance Document has been developed to provide an informational and
easy to follow “road map” to assist communities in their approach to adopt LID. The following outline was developed after multiple discussions amongst the authors on the approach in this document. The following outline was determined for the final document.
I Introduction / Purpose / Applicability II The Case for LID Low Impact Development Defined Justification for Implementation of Low Impact Development
The current storm water management and land development philosophy
Pollutants in Non-point source and why they are a concern The Hydrologic Cycle III Benefits of an LID Stormwater Requirement IV Process for Developing and Adopting LID standards V LID Policies and Performance Standards Issues associated with Implementation of LID Requirements LID Designs and Processes Design Standards
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Cluster Subdivisions and Zoning Codes Green Streets and Parking Standards for LID Rainwater Harvesting and Public Health VI Enforcement and Maintenance Issues VII Public Education and Outreach VIII Reference Documents IX Definitions
A brief summary of each section will be discussed and why it is important for
this document.
Introduction/Purpose/Applicability With any document, we need to introduce our topic and why we have prepared it for the ultimate readers, both in the regulatory and design communities. The purpose of this document is simple and elegant; to encourage the widespread implementation of LID strategies and systems to minimize and improve the quality of surface and ground water that is being adversely impacted by development and our current regulatory system by creating and defining a process that any communities, large and small can use to apply LID.
Applicability is an important issue with LID. It is and continuing to be important to the authors that we develop a logical process to assist communities in this regard. A glaring issue became apparent after reviewing existing regulations that would create problems for the widespread adoption of LID. In many communities, certain municipal, county, state and even federal projects are exempt from local land use regulations. This has led to an “us” versus “them” situation, with developers who must comply with the local rules “us” against all those agencies and groups who do not have to comply with the local rules “them”. How and where LID will be applied in a community is up to the individual community, but the document will stress the importance of clearing defining the applicability of LID regulations. It will be strongly encouraged that the adoption of LID in a community will apply to all projects (private and public) to achieve the highest environmental benefits. The Case for LID
With any document, the topic must be well defined and articulated for all users. “LID is an ecologically friendly approach to site development and storm water management that aims to mitigate development impacts to land, water, and air. The approach emphasizes the integration of site design and planning techniques that conserve natural systems and hydrologic functions on a site.”
Whenever, you ask people to change how you do things, they always want to
know WHY SHOULD I CHANGE THE WAY I DO THINGS. This document provides the rationale for any community to answer this and other questions regarding LID. In short, the justification is very simple. The current development and
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stormwater management philosophy has not worked as intended in many parts of this country. The result has been the degradation of surface and ground water quality and increased flooding as a result of development.
The document also explains why the current regulations and requirements for
stormwater management and land development are not working in this country. In many places, it is simply because the land use regulations are prescriptive in nature and do not require or account for the environmental constraints that may exist on a site. It is the square peg in the round hole problem.
Many in the development and local regulatory communities are not
knowledgeable about the adverse impacts of pollutants found in both construction and post-development runoff. The document provides a simple and readable explanation about the common pollutants found in non-point source runoff. The primary sources of these pollutants are provided as well as the many adverse impacts that they can have on our aquatic resources.
As a major focus of LID is minimizing changes of the Hydrologic Cycle, the
document discuss the various aspects of the Hydrologic Cycle and how development changes these aspects.
Without the discussion of the need for change, we are just creating another set
of rules that will likely not be well received or followed. Background and history are important aspects of the need to move forward with a better way of doing things. People tend to have a short memory of problems and therefore continue doing things the same way with the same predictable results. Without providing the background, we cannot move forward with LID.
Benefits of an LID Requirement
Anytime that the regulatory agency goes to change a regulation, the question of “why” always come up from the development community. With the movement to LID, the “why” gets louder and more pronounced because LID represents a paradigm shift in the development field.
In order to adequately address the “why” question, the community needs to be aware of and be able to articulate the many goals and benefits that can be achieved by implementing LID in their community. Some of the benefits associated with implementation of LID are stated below.
a. Environmental Benefits: i. Preserve the biological and ecological integrity of natural
systems through the preservation of large extents of land ii. Protect the water quality by reducing sediment, nutrient and
toxic loads to the wetland/watercourse aquatic environments and also terrestrial plants and animals
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iii. Reduce runoff volumes in receiving streams
b. Public Benefits: i. Increase collaborative public/private partnerships on
environmental protection by the protection of regional flora and fauna and their environments.
ii. Balance growth needs with environmental protections. iii. Reduce municipal infrastructure and utility maintenance costs
(roads and storm water conveyance systems).
c. Developer Benefits: i. Reduce land clearing and earth disturbance costs, reduce
infrastructure costs (roads, storm water conveyance and treatment systems).
ii. Reduce storm water management costs by the reduction of structural components of a drainage system.
iii. Increase quality of building lots and community marketability. These benefits can only be realized when the many goals of LID, which are elaborated in the document are implemented in the design and approval process. Process for Developing and Adopting LID standards: The document discusses the process for a community to implement LID. The evaluation of the appropriateness of LID and how to implement LID in a community is not a “do it yourself” project for the community. While LID concepts can be applied to any geographic location, standards and processes need to be tweaked for local conditions and issues. Consultants with expertise in LID and land use regulations are needed to assist the community in this regard. The first step for a community is an evaluation and acknowledgement that the current development practices are not working in their community. As these development practices are based upon the communities land use regulations, this acknowledgement leads to the need to revise the necessary land use regulations. The document provides a general process for a community to incorporate LID into the regulatory process. The current system of stormwater management is based upon getting rid of the water from the proposed development and into a natural conveyance system, such as a wetland, stream, river, pond or the ocean as quickly as possible. In general minimal consideration is given to what happens when the stormwater leaves the site or how the discharge of runoff will affect downstream systems. If there are downstream flooding concerns, a detention basin could be constructed that would reduce the post-development peak runoff rate to the pre-development flow rate. While this idea seems logical, it does not account for, nor does anything about the substantial increases in runoff volumes which result from increased impervious areas.
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LID is a completely opposite process to deal with stormwater, so the technical processes associated with LID need to be clearly articulated for user. The document provides an overview of the technical processes that are important to LID, such as volumetric control, water quality issues, flow duration issues and peak rate controls. The document describes in detail, the four main strategies associated with LID, such as Preservation of Vegetation and Soils; Site Design; Stormwater Management; and lastly, one of the most important aspects of adopting LID; Education and Maintenance. If end user are not familiar with LID is and how it works, it will never be widely used. LID Policies and Performance Standards Many of the current land use regulations that are in use today are the main impediment to the incorporation of LID. These regulations are extremely prescriptive in nature, and not very flexible, while LID regulations focus more on specific goals and achieving performance goals. The document provides a template to identify the common impediments in local land use regulations and why they are barriers for LID. To assist users of this document, an actual regulatory audit identifying barriers and impediments of LID has been included as part of the Guidance document. The following is a summary of some of the common issues in existing land use regulations that are either impediments or outright barriers to the adoption of LID. Zoning Regulations:
• Prescriptive standards for residential lots, such as minimum area, minimum frontage and large setbacks,
• Lack of building or total impervious coverage standards for residential lots. While impervious coverage limits are common for commercial & industrial zones, they are rarely defined for residential zones,
• Excessive parking requirements. Many municipal regulations require more parking than is needed for commercial land uses. This leads to substantial increases of impervious cover, increased rates or runoff, increased volumes of runoff as well as increased pollutant loads being directed to receiving waterways,
• Stormwater analyses which only focus on large storm events such as the 25-yr to the 100-yr event. In many cases, reductions in the changes of peak rate are not required by the regulations, but are determined on a case by case basis by the municipal engineer.
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Subdivision Regulations:
• Prescriptive road standards, which require wide pavement width, • Horizontal and vertical geometry requirements that do not permit the road
alignment to fit the natural terrain. • No requirement to evaluate the environmental sensitivity of the site nor any
required to protect these natural resources, • Reliance on structural drainage solutions only. No ability to allow for
deviations from the structural requirements. • Stormwater management focuses on the collection and conveyance of runoff
only as quickly as possible. No standards or design requirements to address water quality issues.
Safety Issues:
• In many rural areas, the need to provide adequate fire protection creates impediments to the use of LID. A common issue has been the local fire authorities who will advise planning agencies not to reduce road pavement widths as it could impede their ability to provide emergency response. There are many viable issues to this issue, both the regulatory agencies appear to be unwilling to entertain solutions out of fear that if the solution does not work and a house burns down because the fire department could not access it, they will be blamed for reducing the road width.
The document also provides concepts and examples of how LID can be incorporated into regulations through case studies. Some approaches have worked well with the result of LID concepts being utilized with good results and in other approaches; LID concepts are still not being applied. The case studies provide opinions as to why certain approaches work or don’t work. Once a community has decided to implement LID, it is very important that the steps necessary to apply LID are understood. The document provides a step by step process for the implementation of LID strategies and provides a discussion of the benefits associated with each major step. An example of this is the application of Environmental Site Design Analyses and how ESD can lead to development which is in harmony with the site features while mitigating hydrologic impacts. The document provides standards for the hydrological aspects of LID treatment systems that are based upon the most current research being performed by a variety of individual and research universities. A unique aspect of LID is the application of performance standards for volumetric reduction as well as water quality improvements. By creating a performance standards and providing a tool box of possible solutions, the designer can develop an appropriate system to achieve these goals.
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The document provides a thorough discussion of the benefits of Cluster or Open Space subdivisions and how to create flexible zoning regulations to achieve these results. The use of these types of development can yield tremendous positive results on the quantity and quality of runoff from the development. Sample language and standards from communities that have these regulations in place which work are provided for the users. Our current road specifications and parking requirements are another of the major barriers to the implementation of LID. The document provides a detailed discussion on advantages of Green Streets, which typically are narrower that our current standards and employ flexible geometric requirements to allow them to more closely fit the natural environment. Examples of the application of Green Streets, such as in Seattle, Washington, and Portland, Oregon, are provided in the document. The document provides a discussion about the current requirements for parking spaces for a particular use and explains how these requirements are barriers to the implementation of LID. In addition, the document provides information from communities, where the typical prescriptive requirements have been modified to encourage LID systems. A key component of LID is the thought that “rainfall is a resource to be used rather than something to get rid of”. Toward this end, a simple idea is the idea of collecting and reusing the rainfall from a residential roof. The document provides examples of different types of collection system that are currently available. One concern with the idea of collecting runoff in an enclosed container is the possibility creating an environment that mosquitoes will find desirable. The document provides resources and methods for addressing this concern.
Enforcement and Maintenance Issues
One of the most common concerns with the requirement of LID treatment systems is the perceived increased maintenance of these systems. Many DPW’s believe that LID systems will require significantly more maintenance than conventional systems. This belief is not based upon any facts, but is the response to the idea of change. Whether you have a conventional drainage system or a LID treatment system, there will be maintenance with both types. The only difference is the kind and frequency of the maintenance.
These concerns tend to become greater when the type of system is not well known. This is especially true with LID systems. The document discusses the potential enforcement and maintenance issues associated with LID treatment systems and provides clear and concise processes to address these concerns.
The document provides sample maintenance agreements that can be used to ensure that LID systems located on private property will be maintained in perpetuity by the end user. By addressing the maintenance issues head on and in a clear fashion,
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it can be shown to the public works department that LID can actually be less maintenance than conventional stormwater systems. Public Education and Outreach A key requirement for the implementation of LID is Public Education and Outreach. Without the knowledge of what LID is, how it works, how it is constructed and maintained, its implementation will be doomed to fail. The document provides a thorough discussion on the key components of the public education and outreach component, so that a community can have all of the stakeholder involved in the development process (regulators, developers/builders, contractors, homeowners) become knowledgeable about LID and the benefits of its implementation. Reference Documents The document provides an updated list of resources about the various aspects of LID. In addition, the document will provide examples of the typical LID stormwater treatment systems with specifications. There are many different thoughts in how you design LID treatment systems, particularly Bioretention and other filtering systems. It is important to provide supporting technical information to justify one approach over another. Definitions Lastly, as many terms associated with LID are not commonly known, a list of definitions is provided for these and other terms used in the document. Conclusion The goal of the guidance document is to provide a road map for the evaluation of existing land use regulations and policies in order to create opportunities for the adoption of LID that can be applied nationally and internationally. Only by the implementation of LID will we be able to create sustainable developments that minimize potential impacts on our natural resources.
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The Farmington River Enhancement Grants: A Tale of Three Towns and the Path to Low Impact Development
Steve Trinkaus, PE, M.ASCE
Trinkaus Engineering, Southbury, CT, 06488 PH (203) 264-4558, Fax (203) 264-4559; Email: [email protected] Abstract This paper describes the process the towns of Harwinton, Plainville, and East Granby Connecticut used to adopt Low Impact Development (LID) strategies into their existing land use regulations under the Farmington River Enhancement Grants, which were administered by the Connecticut Department of Environmental protection (CT DEP). The CT DEP offered grants to communities located within the Farmington River Watershed to retain qualified consultants to review existing land use regulations in order to encourage the implementation of the LID. This paper discusses and contrasts the approach of the three communities. The Town of Harwinton, CT is a predominately rural community in northwest Connecticut having an approximate population of 5,000 residents. Most of the development in town consists of single family residential units on the typical two-acre building lot. There are several public drinking water supply reservoirs in Harwinton, which are owned by the City of Bristol so maintain the high quality of runoff going into them was a concern to Harwinton. The Town of Plainville is predominately an urban environment, located near the southwest corner of the Farmington River watershed. Over 90% of the community has been developed as either medium/high density residential and/or commercial/industrial. This has led to large, interconnected impervious areas in many areas. The Town of East Granby is mostly rural community with scattered agricultural uses in the western portion of the community and commercial/industrial uses clustered around Bradley International Airport. The paper describes the land use issues in each community which drove the process to consider LID. It also shows how LID development strategies were presented for consideration and adopted to address these issues. Lastly, the paper shows how public outreach was conducted to facilitate the adoption of LID.
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The Grant Process and Funds During the 2008 calendar year, the CT DEP received approximately $ 900,000 as a result of an environmental fine within the Farmington River Watershed in northwest Connecticut. The DEP offered communities grants from this fine up to a maximum of $ 50,000 to evaluate the development of revisions to current land use ordinances to encourage the use of Low Impact Development (LID) techniques in future development activities. The grants required each community to hire a planner and technical expert to perform this evaluation based upon their technical expertise. \Eight communities received funding to consider the adoption of LID.
Trinkaus Engineering (Engineering firm) and Planimetrics (Planning firm) were chosen by the Towns of Harwinton, Plainville and East Granby after an interview process to perform this work. The Process. The following process was developed by the project team and used in all three communities. How the process played out in each community is discussed in more detail after this section.
1. Educate the committee on the adverse impacts of development and the benefits of Low Impact Development Strategies.
2. Regulatory Audit 3. Regulatory approach to LID 4. Language and standard changes 5. Bumps in the Road 6. Public Process
The Town of Harwinton Harwinton is a predominately rural community having an approximate population of 5,000. There is only a small area of commercial development in the community, located along Route 118, which runs west to east thru the northern portion of the town. The dominant land use is single-family residential. Most of the town is zoned for 1-acre and 2-acre building lots. Education on Current Development Patterns & Stormwater Management. Presentations on the overall concept of LID, Environmental Site Design, volumetric reduction, water quality treatment and source controls were made to the town to demonstrate how effective LID would be in the community.
The project team had a casual discussion with the committee about the current
land use process in Harwinton. As is very common in Connecticut, the zoning regulations for single family residence are quite prescriptive, defining; minimum area, lot frontage, minimum rectangle and setbacks. These regulations have led to fairly standard “cookie cutter” development patterns of linear roads and rectangular lots. A new requirement of a minimum “buildable area” was adopted by the Zoning
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Commission in 2008. This requirement stated that each lot had to have a minimum of 1 acre of land, exclusive of wetlands and 25% slopes.
Stormwater management was simple and conventional. Standard curb & gutter, and catch basin systems to collect and convey stormwater to a low point, where a detention basin was sometimes installed to reduce the post-development peak rate to the pre-development peak rate for a 25-yr storm event. Receiving streams which received runoff from several residential subdivisions were observed to be experiencing channel erosion and in-channel sedimentation. Regulatory Audit. The first step in the process is the audit of the existing land use regulations. The purpose of the audit is to identify existing land use regulations which are either barriers or impediments to the adoption of Low Impact Development. To this end, the project team reviewed the zoning, subdivision and inland wetland regulations as well as the road ordinance. As zoning regulations are the backbone of land use, the audit was focused on them.
Zoning Regulations. As is the case with most land use regulations, the standards in the zoning regulations were extremely prescriptive and inflexible. There were specific standards which governed lot sizes and shapes. Standards for residential lots did not provide for any flexibility. The regulations allowed a generous 15% total lot coverage, for buildings, driveways and other impervious areas in the residential zones, yet when actual properties were built upon, it appeared that this requirement being exceeded on a routine basis. Part of the reason for this was the lack of a good definition of what was included in the total lot coverage as well as the lack of a requirement to provide a survey after the work was completed.
The standards for off-street parking required an excessive number of parking spaces for common commercial uses, such as office and retail. In all cases, only a third to half of the provided spaces were ever utilized on a regular basis. This has led to substantial areas of directly connected impervious areas.
Some of the other barriers were simply inconsistent language regarding
erosion control, stormwater management processes as well as ambiguous language regarding the preservation of certain natural features. Subdivision Regulations. The subdivision regulations had many conflicts with other town regulations and ordinances. One of the major issues dealt with horizontal and vertical road design geometry that was in conflict with the Town Road Ordinance. The required pavement widths for residential roads were excessive considering the rural nature of the town. The pavement width for all residential roads is 26’ between the curbs with no provisions to reduce the width even when a small number of lots would be served by the road. All cul-de-sacs are to consist of an 80’ paved circle with no landscaped island.
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The drainage standards are very vague and minimal design specifications are provided. The standards only provided for structural drainage to be permitted. One section required that all runoff be directly connected to a receiving waterway or wetland, yet pollution in the stormwater was to be “addressed”. Clearly, this regulation was not enforceable nor did it seem to be applied evenly by the commission.
There is no consideration of flexible development patterns, such as Open
Space subdivisions, where smaller lots are allowed with a greater area protected from development without increasing the density of the development. Inland Wetland Regulations. There are no barriers to LID in the inland wetland regulations. The barrier to the use of LID from a wetlands perspective is found in the commission itself. Towns have established with the blessing of the CT DEP, defined upland review areas outside of delineated inland wetlands. The purpose of these review areas is to allow a commission to review an activity within this area for a potential impact on a wetland or watercourse. However, in many communities which discourage development, the upland review areas become defacto setbacks from the wetland areas, where no activity is permitted, thus reducing the development potential of a parcel of land. Regulatory approach to LID. After the impediments and barriers to LID were identified in the regulations, the project team produced a document discussing these issues and suggested changes to the regulations to eliminate these issues and allow LID to be implemented. The project team recommended language changes for all current land use regulations which would remove the identified barriers to LID and would require the implementation of LID. The most substantial changes were in the zoning regulations, with the smallest changes in the wetland regulations. The project team also strongly recommended the adoption of a LID Manual which would define all the necessary processes for LID. It was shown to the town that other communities tried to simply encourage the application of LID, but this encouragement rarely resulted in the LID being applied. When an applicant is presented with the option of using a new technique such as LID or continuing to use a standard detention pond to handle stormwater, the standard detention pond is chosen because both the designer and applicant are comfortable with it as a stormwater management tool. The driver of this mentality is “fear of the unknown” or in this case, LID. So, if the community wanted LID, they needed to require the application of LID strategies.
It was also suggested that a Density Factor be incorporated into the zoning regulations which would allow a developer to easily determine the maximum number of residential lot which could be placed on a property. The Density Factor does not specify the minimum size of a residential lot, only the number of lots. When coupled with the ability to cluster the residential lots using Open Space subdivision language, the lots can be placed on the land most suitable for development and preserve large areas of protected land. When coupled with the application of Environmental Site Design processes, developments would be fit the natural landscape, provide for
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protection of sensitive environmental areas and create a sense of community for each project. Language and standard changes. The following is a summary of suggested regulatory changes initially provided to the committee with the suggestion of approaching each individual agency with the changes to their regulations.
Remove all language related to stormwater management from the regulations and replace with simple language referring to LID Manual,
Place all stormwater requirements in new LID Manual, Define performance standards for stormwater in the LID Manual, Adopt LID Manual, Adopt Flexible Development Patterns & Density Factor, Reduction of road width based upon number of units to be served, Increase flexibility in the horizontal and vertical geometry for roads, Reduce number of parking spaces required for commercial uses, Permit the use of alternative surface materials for parking lots,
Bumps in the Road. While the Committee and Board of Selectman voted unanimously to fully support this approach, the individual commissions and departments were more wary. Department of Public Works (DPW) did not want narrower roads due to perceived issues with safety (fire trucks on narrow roads), and snow plowing. They also did not want depressed islands (for Bioretention) due to the potential of black ice forming on the road surface. The project team removed the offending language and DPW supported these changes.
The planning commission felt that flexible development patterns would increase the density of development on a site, despite assurances from the project team that this would not be the case, and this was demonstrated by applying the proposed LID processes on a recently approved residential subdivision. It was actually shown that nine less lots would be created, and the area of dedicated Open Space increased by ten times. These issues were removed from consideration and Planning was supportive of the LID Manual and other changes.
The zoning commission was the biggest surprise in a negative way. The
zoning commission was not supportive of adding a Density Factor, Open Space subdivision standards and Environmental Site Design standards to their regulations. The members stated that in 2006, the zoning commission proposed a regulation defining a “Buildable Area” for residential lots. It was widely opposed by not only landowners, but also by the Planning and Wetlands Commissions and the zoning commissioners were widely criticized for adopting the standard anyway. The commission stated that they were worried that these changes to facilitate LID would subject them to the same type of criticism and wanted to avoid it. Both Wetlands and the Board of Selectman remained steadfast in their support of LID in general, but were concerned about the attitude in both Zoning and Planning.
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The LID process took a huge step back because of these political issues. Based upon feedback from the Commissions, the project team revised the approach to simply focus on providing Groundwater Recharge and Water Quality Volumes for new development projects by referencing the State Stormwater Manual. The LID Manual became a document of recommended design and construction practices to follow if an applicant was to use LID. Environmental Site Design and Flexible Development patterns were eliminated from consideration and Pollutant Loading Analyses were not included as a requirement. Public Process. After all the proposed language changes were made, meetings were held with each commission to make sure they were comfortable with the revised products. They were, so a series of public hearing were set by each commission for January 2011 and the regulations were adopted on March 1, 2011 The Town of Plainville There is a wide variety of residential, commercial and industrial uses in the town. The majority of the town has flat to slight slopes and these areas have begun to experience some adverse impacts due to stormwater. All stormwater is discharged to either the Farmington or Quinnipiac Rivers. When the river levels rise, backwater conditions occur within the existing stormwater lines causing flooding problems throughout the town. Except for the occasional detention basin, historically, there has been minimal attention paid to stormwater. The approach to the inclusion of LID in Plainville started out similar to Harwinton. Education on Current Development Patterns & Stormwater Management. Because a majority of the town has been developed, the team focused on the application of LID retrofits to improve water quality and reduce runoff volumes in commercial areas. Some of the LID retrofit ideas presented to the town were LID planters; curb bump outs, linear bioretention systems and pre-packaged systems, such as Filterra and Modular Wetlands.
A majority of the residential development consists of lots less than ½ acre in size, which are served by a public road network. These residential areas handle their stormwater in a simple way: pipe it away and let the downstream person deal with it.
The project team reviewed several projects which had recently been approved
by the town and provided a written narrative has how LID strategies could have been applied to them to improve the stormwater management plan. This had a very positive effect on the town engineer, who had expressed reservations about LID in the beginning.
The project team, along with the town engineer and planner met with some
local developers and design engineers to solicit their thoughts on the current
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regulations and the changes which would occur with LID. While the designers in particular had concerns about LID, the developers were more open to the concept after the economic benefits of using LID versus conventional drainage systems were provided. Regulatory Audit. An additional goal of the audit was to update the reorganize the sections of the Zoning Regulations. The town planner stated that the current format of the regulations were very difficult to use and updates to sections were simply added to the end of the regulations and not incorporated into the appropriate sections. As part of the LID process, the Zoning regulations would be reformatted to become user friendly. Zoning Regulations. As is the case with most land use regulations, the standards in the zoning regulations were extremely prescriptive and inflexible. There were no limitations on either building or total lot coverage for any of the residential zones, so many of the residential lots had impervious covers greater than 80% of the lot area based upon reviews of property survey maps.
Parking requirements were extremely excessive for many retail uses, which
resulted in large, paved parking areas, only 40% of which was actually used during busy times. A review of town aerial mapping and site surveys showed that existing large scale commercial/industrial uses had impervious coverage which exceeded 80% while the regulations permitted a maximum of 50%.
Specifications for stormwater management were conspicuous by their absence
in the Zoning regulations. Subdivision Regulations. These regulations had a pleasant surprise in them. Open Space subdivisions were permitted and the standards to apply them were relatively well defined. However, discussions with the town planner showed that this provision was rarely used by a developer. So what was the problem? A deeper reading of the regulations revealed a provision that limited the percentage of wetlands and steep slopes in the open space area. This led developer to forgo the Open Space concept, which required a minimum 50% set-aside and use the conventional approach, where the set-aside was only 10%. He would have to “give up” less good land under this approach.
The road standards required pavement widths up to 26’ for residential developments and wider roads for Collector or Arterial classifications. The regulations stated that roads should be laid out in a gridiron pattern. Clearly, this requirement does not allow road to follow the natural contours at all.
The stormwater regulations had provisions to address water quality, work
with the natural land form, minimize impervious areas, infiltrate runoff where possible, reduce peak rates to minimize adverse impacts on streams and wetlands and provide maintenance protocols. Based upon a review of approved residential and
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commercial projects these requirements were not being addressed by the applicants nor did the commission require the applicants to address these issues. There were no performance standards in the regulations for these items so it was left up to the applicant to determine what was appropriate for the particular project.
There is also a section which requires the mapping of natural features, such as
wetlands, steep slopes, fragile areas, noteworthy flora and fauna and even suggests that these areas be preserved. But once again, this was not enforced. Inland Wetland Regulations. There are no barriers to LID in the inland wetland regulations. Plainville defined the upland review areas to be 50’ in width. In Plainville, the Wetlands Commission did not consider the upland review area as setback and was very much in favor of the implementation of LID. Regulatory approach to LID. The project team recommended language that would remove all stormwater language currently in the regulations and incorporate in a LID/Stormwater Manual. The Manual contained an education section on stormwater and LID. Performance standards were incorporated for reducing runoff volumes and reducing pollutant loads in the runoff. In additional, the Environmental Site Design Process was incorporated as the first step in applying LID to encourage the largest environmental benefit.
The Manual also addressed redevelopment projects in the commercial and industrial zones. It was initially the project team’s suggestion that 50% of the required performance standards would need to be met, even if the total impervious area was being reduced. The town planner and town engineer took the position that they wanted to substantially improve the water quality from redeveloped commercial and industrial sites, so the standard was revised to require full compliance with the LID performance goals even if the impervious area was being reduced.
As most of the town was already developed, small, but, numerous increases of
impervious areas in the residential zones would result in increases of stormwater runoff. A section was created in the manual to address this issue with simple to apply provisions, but the Planning and Zoning Commission had concerns about imposing a “burden” on these residents at this time. This section was made part of the Manual, but was noted that it was not in effect at this time.
A unique feature of the Manual is two matrix tables to assist designers in
choosing the most appropriate system(s) to meet the LID performance goals and evaluate the pollutant removal capabilities of each type of treatment system. Language and standard changes. The following is a summary of regulatory changes provided to the Planning and Zoning Commission:
Remove all language to related stormwater management from the regulations and replace with single line referring to LID Manual,
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Place all stormwater requirements in new LID Manual, Define performance standards for stormwater in the LID Manual, Adopt LID Manual, Reduction of road width based upon number of units to be served, Reduce number of parking spaces required for commercial uses, Permit the use of alternative surface materials for parking lots,
Bumps in the Road. While the project team had initial concerns about the town engineer supporting the shift to LID, he soon became a very positive advocate for the LID approach and provided his support to the commission. Public Process. The reformatted zoning regulations along with the slight changes to them and the subdivision regulations went to public hearing in September of 2010. There were only positive comments from the Commission, staff and the public. After 45 minutes, LID was fully adopted in the Town of Plainville and the requirements became effective on December 1, 2010. The Town of East Granby
East Granby is a small community having an approximate population of 4,500. Most of the residential development consisting of single family homes on 0.25 acres to 1.00 acres. The majority of the community is tributary to the Farmington River, which is beginning to show some adverse impacts, such as bank erosion due to stormwater. The approach to LID. An introductory presentation was made to the Planning & Zoning Commission on LID and also described the benefits of LID. After reviewing the approach used in Plainville and Harwinton to adopt LID, the commission was in favor of this approach used in Plainville. The regulatory audit was done next. Zoning Regulations. As is the case with most land use regulations, the standards in the zoning regulations were extremely prescriptive and inflexible. While there is a provision for Planned Residential Developments (open space subdivisions), the application of this regulation still resulted in cookie cutter type developments only with smaller lots.
Parking requirements were extremely excessive for many retail uses, which resulted in large, paved parking areas, only 30% of which was actually used during normal times. Specifications for stormwater management were conspicuous by their absence in the Zoning regulations. Subdivision Regulations. These regulations had a pleasant surprise in them, a provision to evaluate the natural resources on a site. Problem was that the natural resource assessment provision was never enforced by the commission.
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The road standards were very prescriptive with very little flexibility. Roads had to have curb and gutter stormwater conveyance systems, unless alternative systems were recommended by the Town Engineer.
The stormwater regulations very also very prescriptive and focused on peak
rate control of the 25-year storm event. In many cases, detention basins were not required even though there were increases in the peak rate of runoff. Inland Wetland Regulations. There are no barriers to LID in the inland wetland regulations. Regulatory approach to LID. The project team recommended language that would remove all stormwater language currently in the regulations and incorporate in a LID/Stormwater Manual. The town planner requested that two documents be created. One, the LID/Stormwater Design Manual contained performance standards for the hydrologic aspects of LID, construction specifications for LID and Conventional treatment systems, definitions, plant list, stormwater management checklist, sample maintenance agreements for LID systems and LID references. The second document, called an Education Booklet discussed the impacts of development/stormwater, what is LID, an overview of LID strategies and the Environmental Site Assessment process. Examples of the types of LID systems which could be used to address Groundwater Recharge, Water Quality, Water Quantity and Pre-treatment systems were also provided. Public Process. At the writing of this paper, the town is currently reviewing the manual and education booklet with an idea of public hearing being held in September of 2011. Conclusion
While all three towns started down the same path toward implementing LID, they took very different paths to the end result. Plainville adopted the most complete approach to LID. In Plainville, the town planner, town engineer and the land use commissions were strongly in favor of adopting LID which provided the critical support for LID. In addition, the town staff and the project team took the time to meet with developers, builders and design professionals to discuss LID and demonstrate how it would be beneficial to their projects.
Harwinton which did not have a town planner and only used a consulting firm
for engineering services hindered the consideration of LID as there was no one to lead the LID effort. Another hindrance was the lack of public outreach by the land use committee to tout the benefits of LID to the residents and the development community.
In East Granby, the town planner and town engineer were clearly in favor of
adopting LID and their support was very important in convincing the land use
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agencies of the benefits that the town would experience with adoption. The town planner also hosted a meeting with local design professionals so that the project team could discuss the changes which would occur with the adoption of LID and gain their support.
References Trinkaus, S. (2008); Town of Tolland Design Manual, adopted January 28, 2008.
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Beyond the Green Infrastructure: What do you do with the trash and debris?
Hans de Bruijn, Sr.
Environmental Manager, Fresh Creek Technologies Inc. 1384 Pompton Avenue Suite 2, Cedar Grove, NJ 07009. Phone 800 741 9486 Abstract
Low Impact Development (LID) storm water management practices (BMPs)
are preferred methods for the treatment of stormwater runoff to remove certain pollutants from the runoff before the storm water evapotranspires, enters our streams or recharges groundwater. These systems are preferred because LID BMPs can be retrofitted into the existing landscape to intercept runoff without installation of a large amount of additional infrastructure. The optimum conditions for LID BMP’s are where the runoff has low velocity and low volume.
LID BMPs are not designed to remove trash and debris from stormwater runoff. Such pollutants are untreated, impair the functionality and in view of LID BMP’s. They remain as an unsightly reflection of urban living. Simply put, LID BMPs are only part of the solution for stormwater treatment. Without the use of other technologies in a treatment train configuration, removal of trash and debris will remain beyond the capability of urban LID BMP designs.
Fresh Creek Technologies, Inc. recognizes this problem and directs its efforts on developing cost efficient ways to remove trash, debris and other pollutants from stormwater runoff. This approach is complimentary to and an enhancement to LID BMP designs. From their research and development several unique systems have been designed that meet the parameters of sound, scientifically based engineering; low initial installation costs and cost effective long term operation and maintenance. Fresh Creek Technologies
Fresh Creek Technologies’ goal is to remove trash, debris and other pollutants
from storm water, CSO’s and other run off conditions, in an efficient, manner before these pollutants enter our ground water, rivers, streams and other water receiving areas. The development of urban and suburban communities has altered water and drainage courses. Meandering streams and creeks have been encased in pipes and culverts; and impervious surfaces have altered the flow of water in many of our communities.
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Concomitant with this development has been an increasing population density which has caused a steady increase of trash and debris. This unsightly, non- biodegradable sea of trash and debris such as plastic bags and bottles, Styrofoam food containers and aluminum cans, is carried by the storm water runoff. In addition, these pollutants provide a breeding ground for rodents, insects, mosquitoes and bacteria. The inevitable result of dense population growth is a degradation of the environment, increased costs on an already overburdened local government and the erosion of property values.
Fresh Creek’s goal is to provide site-specific solutions targeting trash, debris and other pollutants that can be retrofitted into developed areas or designed for new site development as an addition to an LID BMP design. Fresh Creek Technologies, Inc. will continue to work with national, regional and local leaders to develop environmentally attractive solutions to water pollution for their communities. Background
Predominantly natural landscape facilitates evapotranspiration and infiltration,
processes which prevent pollution and erosion. They are desired natural pathways for rain to complete the water cycle. Development alters these natural waterways with streets, curbs, sidewalks, parking lots and buildings. The water cycle continues with these manmade obstacles. In addition to these permanent additions to the landscape, modern society continuously rains trash and debris on its surroundings. Obvious examples are the ubiquitous plastic bags and bottles, disposable food containers, cigarette butts, etc.
Health and safety concerns encouraged civil engineering designs that remove runoff from surface areas as quickly as possible. This acceleration and alteration of the water cycle is disruptive and creates many other problems. The monetary and environmental costs are great and will affect many generations.
The flow of runoff into pipes, concentrating and altering the natural water retention up stream causes stream flooding, erosion of surfaces and stream banks, surcharging of streets and an outdated storm water conveyance system with nutrient rich leaves and other vegetative matter, pollutants such as, trash, oil, sediment, heavy metals, phosphorous, nitrates and other compounds.
Recharge of groundwater is short circuited as the runoff is captured and instantly drained far from where it originated.
LID BMPs work best when the goal is runoff volume reduction. Small drainage area flows can be directed into LID BMPs to promote infiltration near where the precipitation occurs. Green roofs and small bio retention areas such as rain gardens and bio retention swales will reduce volume and are easier to maintain where the concentration of the above mentioned pollutants are low; such as from rooftops.
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As the runoff traverses the landscape pollutants are swept up and concentrate in the runoff. The diverse nature of the collected pollutants requires a comprehensive approach for optimum removal from the runoff. Generally, a large drainage area with a dense population will result in more types of pollutants in greater concentrations. The landscape has been re-shaped by civilization’s demands and now the time has come for us to confront the physical realities of storm water pollution management and treatment. We must bring sound scientific principles and analysis to the problem or we may never attain the “swimmable and fishable” waters objective of the Clean Water Act. A balanced approach is necessary, as society demands progress and convenience even if the inevitable result is a continued barrage of trash, debris, sediment, oil, grease, heavy metals and fertilizers. Education and regulation fight the uphill battle to alter human behavior. Unfortunately,
“We have met the enemy and it is us”. Reality Check
The road to “swimmable and fishable waters” is paved with good intentions.
But good intentions without scientifically based action are not enough. Fostering scientific innovation that effectively removes the pollutants without stifling development must be the goal. Environmental stewardship and economic growth are not mutually exclusive if open mindedness and a spirit of compromise prevails.
“Smart growth is achievable”
Simple observation reveals that oil, grease, sediment, plastic bags and bottles; disposable food containers, cigarette butts and any other type and kind of pollutant will accumulate wherever people live. Littered open channels are open sewers, a visual squalor. It is imperative that effective solutions attack this urban blight. Failure to explore all technologies will doom us to live in an unsightly and health threatening environment.
Reality Options
Whatever the selected remedy ongoing operation and maintenance functions
and costs must be considered. A storm water BMP that functions properly will capture pollutants. If so, then what is the most efficient way to preserve its functionality before it fails as the result of deferred maintenance? An answer is Pretreatment of the inflow before it enters the BMP with a reasonable method that preserves functionality and is cost effective.
Pre-treatment Methods
SENSIBLE PRE-TREATMENT concentrates the pollutants at an easily accessible location for maintenance crews to collect the waste. It does not use power driven equipment, and relies on gravity driven flow (Hydro-Dynamic). SENSIBLE PRE-TREATMENT uses the most effective methods for collection of the pollutants.
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Since water is not compressible and flows downhill, there is only a finite opportunity, time and space to remove its pollutants. For example:
Figure 1. Even clean curb cobbles in low density neighborhoods are buried under sediment.
Figure 2. Sediment and trash decorate the swale 1. A flat surface screen could be placed in the pipe opening to allow both a flow
through area and collection surface. However, as the screen captures pollutants, it eventually blinds the openings and flow is blocked. The screen and flow through surface can be expanded by replacing the flat screen surface with a three dimensional net. Figure 3 shows an example where a three dimensional netting surface increases the flow through area by 640%. This provides a longer time period of functionality at greater flows and increases the required maintenance intervals. The “net benefit” is higher removal rates for longer time periods with lower operational and maintenance costs.
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Figure 3. Three dimensional netting
The level of treatment is determined by the size of the net and the size of the openings. Los Angeles County requires 97% removal and ¼” openings. Washington Area Sewer Authority (WASA) 83% removal (AWS 2008) and 1/2” openings. These are estimated percentages, because they are functionally dependent on perpetually changing conditions. They provide the following “net benefits”.
a. Trash captured within easy reach of maintenance crews. b. Bulk capacity of debris and trash up to 1000 lbs. (drip dry weight) while
maintaining flow through the system. c. Stretchable screening surface permits increased flow through capacity as
water pressure increases. d. Easy disposal of the spent netting bag and replacement with a fresh netting
trash trap. e. Low health risk to workers as there is no need to empty the nets.
2. Nets are designed to trap floating matter. Most suspended sediment particles pass through, but some sediment is captured among the trash and debris.
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Sediment particles generally sink in direct proportion to the square of their size (i.e. Stokes’ Law). Thus, in storm water pretreatment situations, it becomes cost prohibitive to remove particles smaller than 30 Microns. The particle is suspended in a droplet of water and sinks because it is denser than the water. The water rises in the water column toward the out flow invert. If the particle is to remain in the device, i.e. below the invert, it is necessary that the particle sinks faster than the water rises. This reality affects the need for settling area in the same exponential proportion in order to reduce the lift rate of the water. This exponential increase in requirement of the settling area as particle size decreases linearly, makes particle removal by gravity cost prohibitive in ranges below 30 microns. Controls such as coagulation, to flock particles and exceed their individual settling speed by their combined settling speed are not practical. Neither can we regulate rainfall intensity to control the flow. All hydrodynamic separators rely upon gravity to remove sediment before the storm water in which it is encased exits the device. Thus, methods that increase settling area at low cost facilitate sediment removal at the lowest cost. The gravitational settling methods discovered by Hazen, Camp, and Weijman Hane (the “inclined plate” design) (Hendricks 2006) is widely used in potable water treatment and industrial applications, albeit at flow rates far below those encountered in storm water applications. Yet, recent research at Alden Laboratory in Holden, Massachusetts, proved removal of all sediment particles >49 micron and 95% of all sediment particles >30 Microns at a 22.5 gpm/ft2 Surface Overflow Rate per inclined plate cell (Humphrey 2008). Since the gravity vector is vertical the settling area is the plan projected area of the cell. The cell is inclined to facilitate self-cleaning. However, the spacing between the cells is only 2 Inches. The success of this design rests on Allen Hazen’s conclusion. Hazen concluded: “The only way in which the depth influences the efficiency of sedimentation is in preventing bottom velocities too great to allow deposition of sediment”. And Allen Hazen made proposition 14 in his 1904 paper: “As the action of a sedimentation basin is dependent upon its area and not upon its depth, one horizontal subdivision would provide two surfaces to receive sediment instead of one, and would double the amount of work that could be done”. The overlapping of settling cells increases the efficiency of the system footprint. For example: the hydrodynamic inclined cell settler that Alden Laboratory tested has an effective settling area of 115 square feet, but a footprint of 45.5 square feet. These design features lead to substantial efficiency increases that are not found in conventional designs. With the most popular settling cell model Terre
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Kleen1 TK18, the following characteristics have been shown in the full scale laboratory tests: a. Terre Kleen™ TK18 has 18 parallel operating cells and the design guarantees
each cell receives Q.18-1 in flow volume and exposes 6.407 Ft2 of horizontal settling area to the flow. Thus Q1/A1 = Q2/A2 etc. = QTotal/ATotal.
b. Total cell settling area is 115 Ft2. c. Total foot print area is 6.5 feet by 7 feet or 45.5 ft2. d. With a Particle Size Distribution sample of 1-1000 Micron the device is
certified by NJDEP to remove 57.8% of the mass at 18 gpm/ft2 of cell settling area.
e. Similarly if OK1102 PSD samples of 52-212 Microns are used, it removes 100% of the mass under the Net Annual Calculation of NJDEP at 22.5 gpm/ft2.of cell settling area.
f. 97% of all particles over 30 Microns were removed at 22.5 gpm/ft2 of cell settling area.
g. The efficiency per foot print of device is 100% removal of OK110 sediment at 56 gpm/ft2 of device foot print area.
h. Scaling of the device is predicated on the repeated use of identical settling cells. For example: the Terre Kleen TK18 could be designed to receive 144 gpm per cell and have a capacity of 18 x 144 = 2592 gpm. A Terre Kleen TK54 would then have 114 x54 = 7776 gpm capacity.
Conclusion
Pre-Treatment of storm water from street level environments concentrates the major pollutants at an accessible location where efficient netting trash trap technology and inclined cell sedimentation technology can separate the pollutants from the water and maintain a relatively small foot print and affordable cost. Both technologies should be incorporated in the treatment train arrangement to reach maximum system efficiency.
Following a storm event the pre-treated water can be stored in detention or recharge facilities and be filtered by the soil or by manufactured filters to polish the effluent to even higher quality levels. References Anacostia Watershed Society (AWS). "Anacostia Watershed Trash Reduction Plan."
2008: 4-17, <http://www.anacostia.net/restoration/Reports_and_Data/AWS_Trash_Reduction_2008.pdf>.
1 Terre Kleen™ is a trademark of the hydrodynamic separator produced by Terre Hill Storm water Systems, US Patent 6,676,832B2. This component is the stage two separator in Fresh Creek Technologies Inc. Site Saver™. 2 OK 110 by US Silica in Oklahoma is discontinued, but US Silica substitutes “FINES SPECIAL” from their plant in Berkeley Springs, West Virginia.
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Hendricks, David W. Water Treatment Processes Physical and Chemical. Taylor & Francis, 2006.
Humphrey, Amie N., E.I.T. (2008)“A Comparison of Laboratory Testing and Theoretical Analyses of Sediment Processes in a Separator Unit.” Alden Research Laboratory, Holden, Massachusetts, 2008, <http://www.terrestorm.com/press_research_Humphrey_Comparison.pdf>.
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2
Measuring the Cost-Effectiveness of LID and Conventional Stormwater Management Plans Using Life Cycle Costs
and Performance Metrics
J. Alex Forasté, P.E.1, Robert Goo2, Joel Thrash, CPESC3, Lisa Hair, P.E.4
1Williamsburg Environmental Group, Inc., 1011 Boulder Springs Drive, Suite 225, Richmond, VA 23225; PH (434) 760-3513; email: [email protected] 2U.S. EPA, Nonpoint Source Control Branch, 1200 Pennsylvania Ave. NW MailCode 4503T, Washington D.C. 20460; PH (202) 566-1201; email: [email protected] 3Cardno JFNew, 11156 Luschek Drive, Cincinnati, OH 45241; PH (513) 489-2402; email: [email protected] 4U.S. EPA; Nonpoint Source Control Branch, 1200 Pennsylvania Ave. NW Mail Code 4503T, Washington D.C. 20460; PH (202) 566-1043; email: [email protected] Abstract
This paper outlines a methodology to quantitatively measure the cost-effectiveness of stormwater management plans by linking runoff pollutant load removal and volume reduction performance rates to long term life cycle costs. A step by step approach to calculate cost-effectiveness is provided and one case study presented to demonstrate the methodology. The EPA has applied this methodology to four case studies, each of which compares a built low impact development (LID) project to an alternative conventional design approach. The conventional designs make heavy use of two land cover surfaces that have become dominant in many of today’s existing developments: surface parking lots and turf grass cover. The results are reported in units of annualized cost per pound of nutrient removal ($/lb/yr) and annualized cost per cubic foot of runoff volume reduced ($/cf/yr). Findings show that the LID plans analyzed were four to six times more cost-effective, on average, than the alternative conventional designs. A key finding was that LID stormwater systems exhibited higher performance rates at a lower cost, thereby realizing a ‘compounding effect’ when compared on a cost per performance basis. The results are compared to 43 additional projects identified in a literature review. In addition, a total of eight case studies found that the LID projects cost 19% less on an average capital construction cost basis, and could provide up to twenty additional benefits beyond water quality, than the conventional plans. Introduction
This paper summarizes the methods and key findings of a study recently completed by the Nonpoint Source Control Branch of the U.S. EPA called Achieving More Cost-Effective Stormwater Management Plans using Low Impact Development
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(LID) Strategies. A more comprehensive presentation with additional details can be found in that report. To request a copy, please contact the authors of this paper. Capital Cost Reporting Stormwater & Site Costs. In the financial context of comparing conventional stormwater management plans to competing LID plans, it would seem evident to make the comparison on the basis of capital construction costs. The U.S. EPA (2007), ECONorthwest (2007), UNHSC (2011) and others have made these comparisons for several projects and found that LID projects tended to cost less than the conventionally designed projects in the majority of cases. Capital costs are a key driver and important basis for decision by many owners and developers. However, basing a financial decision solely on this basis ignores important considerations, such as long term maintenance costs, potential operational savings, and social and environmental benefits.
BMP Unit Costs ‘in Space’. Site development construction bids are often derived on the basis of unit costs. Material, labor, equipment, and other construction related quantities are estimated and multiplied by unit costs to derive budget line item elements and ultimately, with other considerations such as profit and contingencies, the total project cost. In this context, it follows that BMP installation costs are commonly reported on a dollar per unit basis. Pervious concrete, permeable pavers, green roofs, and rain gardens may be estimated - at least at a planning level - on a cost per square foot ($/sf) basis (e.g. UNHSC 2011, MMDS 2009). Cisterns, retention basins, and bioretention cells are commonly reported in a dollar per gallon, or per cubic foot ($/cf) basis (Weiss 2005, 2007). The relationship of these BMP storage unit costs to their long term cost per volume reduction capacity is explored in the Results section.
BMP Unit Costs ‘in the Ground’. BMPs, in some cases, are considered as individual elements that can be designed independent of the immediate area surrounding it. In other words, a uniform unit cost is applied irrespective of specific site conditions that may incur cost. For example, a bioretention cell may require significant grading to tie the flat bed bottom and banks into the topography around it, if located on a hill. Above ground cisterns may require a structural foundation pad if located on soils with low bearing capacity. Detention ponds may require additional clearing and grubbing, as well as land acquisition costs to accommodate the additional land area where they are located. Consideration of the conveyance systems required to drain runoff to these BMPS should also be accounted for, as the earthwork and infrastructure needed to ‘tie’ these systems into the site up and downhill, are intimately associated with the total implementation BMP cost. Stormwater Costs per Acre. Another common format used to report stormwater capital costs is to represent them in terms of cost per developed acre ($/acre) (Olsson 2007), or per impervious acre (CSN 2010a, b; CDM 2010). In some cases, development types (commercial, low density residential, etc.) are specified to
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more accurately portray the intensity of infrastructure, and in others they are not. These rough estimates provide useful planning values to scale up the potential costs of large projects, particularly in the absence of any other information. In some cases though, the cost per acre may represent development costs with no treatment (i.e. conveyance and drainage only). In another case, it may represent treatment of the first ½” only; and in another, retention of the 95th percentile rainfall event. These costs do not indicate the standard to which plans were designed, nor how effective the selected practices are. In this sense, a cost per acre metric may make comparisons from one plan to another difficult, as the treatment standards are embedded and the relationships unclear. Life Cycle Costs Shifting Decision Basis from Capital Costs to Life Cycle Costs. While designing for life cycles has taken on a significant role in the building energy efficiency industry, it has not gained much ground in the stormwater industry. Long term operations, maintenance, high performance, efficiency, resource savings, and design life considerations are all lost when focused on the immediacy of capital construction costs only. Whether in the form of reduced corrective actions, decreased purchases of municipal water and commercial fertilizer, utility fee reductions, extended design life, or even revenue generation through the harvesting of ‘wastes’ and water, none of these considerations can be factored into a capital cost only assessment. Over the length of a project, these considerations can become significant. As stated by Black and Veatch (2009), a life cycle cost analysis that accounts for operations and maintenance and return on investment, provides for the most comprehensive assessment of LID economics.
While maintenance costs for LID BMPs are very gradually becoming more
widely documented and available (U.S. EPA 2005, 2004, CWP 1998, Weiss 2005, 2007, Olson, Roesner, Urbonas, & MacKenzie 2010, Erickson et al. 2010, WERF 2009), the maintenance requirements of the alternative conventional surfaces that would take their place are often forgotten or not considered at all.
Cost-Effectiveness: Linking Performance and Cost
Although BMP unit and site plan costs are becoming more publicly available, the focus is usually on installation costs (e.g. $/cf, $/acre). While this data is useful for budget planning purposes, it does not link performance to costs. This missing link was also noted by Brown and Schueler (1997) who stated that construction costs do not provide a basis for developing the relationship between cost and effectiveness. The implications of making this link are important and informative, as it enables financial resources to be utilized in ways that will achieve the greatest results. The Office of Management and Budget (1992) defines cost-effectiveness as “a systematic quantitative method for comparing the costs of alternative means of achieving the same stream of benefits or a given objective”. They go on to describe a program or project as exhibiting “cost-effectiveness if, on the basis of life cycle cost analysis of
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competing alternatives, it is determined to have the lowest costs expressed in present value terms for a given amount of benefits.”
A few studies and municipalities have reported capital construction costs per
pounds of pollutant removed or volume of runoff reduced over one year. This has the effect of dividing construction costs by only one year of pollutant load removal following installation however, which effectively inflates dollar per pound removed values b neglecting the subsequent years of pollutant removal after the first year. A recently completed model called SUSTAIN quantifies pollutant load reductions and flow abatement in urban areas -- using SWMM, HSPF, or other model -- comparing performance metrics (% removal) to the associated user-defined costs for hundreds of alternative plan scenarios. An optimization algorithm is used to yield the most cost-effective solutions curve matching desired performance levels to associated costs (Shoemaker et al. 2009). The tool is very useful, however due to the level of effort and sophistication needed for its application, may be most useful on scales larger than individual sites, which is the focus of this study. Additionally, it only focuses on capital costs, and does not currently consider life cycle costs.
Maintenance Requirements of Conventional Land Cover Surfaces
ASPHALT SECTION WITH UNDERLYING CLAY
TURF HAS BECOME A DOMINANT LAND COVER
While permeable pavement and bioretention cells may require street sweeping and vegetation management, respectively, the materials that may typically take their place – mainly asphalt and turf – also have maintenance requirements. Asphalt requires periodic crack sealing, milling and overlay, and may be more susceptible to freeze/thaw cycles with their shallower base, potentially affecting design life. Many turf species are considered high input land covers, and may require irrigation system maintenance, water purchases, fertilizer and herbicide product purchase and application, and mowing, all of which require recurring costs and affect stormwater performance. Therefore, the net capital cost and net maintenance requirements of BMPs may be a more appropriate measure, and should be considered in the context of this question –
“What would replace this BMP if it was not installed and what
maintenance costs would that surface require?”
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Olson, Urbonas, Mackenzie, Chenard & Roesner (2010) developed a spreadsheet based tool called BMP RealCost to estimate the cost-effectiveness of BMPs by estimating life cycle costs and dividing by pollutant load removal rates over a multi-year period. Results are reported in a dollar per pound of pollutant removed, among other metrics. Life cycle costs include maintenance, administration, land, and debt service costs. Both first year and annualized costs are reported.
This study is most similar to Olson et al. (2010), however also includes site
costs – beyond the individual BMPs - that may be affected by different design approaches, such as pavement width and storm drain pipe length and diameter reductions. In addition, avoided maintenance costs, such as those associated with conventional asphalt in place of permeable pavement, turf in place of bioretention, and savings realized from rainwater harvesting are accounted for in this study. Framework to Measure Cost-Effectiveness
The methodology presented here provides a way to examine whether changing designs based on either performance or cost gives the designer a more cost-effective design over the life-cycle of the system. The basic framework of the methodology used to measure cost-effectiveness in this study includes the four basic elements shown below.
Step by Step Process to Measure Cost-Effectiveness
The following describes the step by step process taken to measure cost-effectiveness of the four case studies analyzed. It is intended to outline and communicate the process used for this study: Step 1: Measure Stormwater Performance. Calculate annual pollutant load removal performance in terms of pounds removed per year (lbs/year), cubic feet of runoff retained per year (cf/year), or other parameter of interest. In this study, both BMP nutrient removal efficiencies and volume reduction capacities were used to calculate total load reduction rates. These two processes are identified for a typical bioretention cell in Figure 1 below.
Linking Performance to Life Cycle Costs
Step 1 – Measure Stormwater Performance (cf/year, lbs/year)
Step 2 – Estimate Capital Construction Costs ($) Step 3 – Estimate Life Cycle Costs ($ NPV) Step 4 – Calculate Cost-Effectiveness ($/cf/year, $/lb/year)
By dividing annualized life cycle costs by stormwater performance - annual pollutant load removal rates and annual volume reduction rates - the two are tied together and linked by a cost-effectiveness metric. This value decreases (becoming more cost-effective) as either performance is increased or cost is decreased.
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Figure 1. Bioretention Pollutant & Volume Reduction Processes (Source: Adapted from Water Street Studio 2011) For this study, the four hydrologic soil groups and three land cover types of
impervious, managed turf, and undisturbed forest were used to characterize contributing drainage areas. A baseline condition using a post-construction site design layout with no Stormwater Management (SWM) controls was established, and compared to a site layout that included SWM controls. The difference in annual pollutant loads between the baseline condition and condition of interest is the load reduction that should be reported in this step, for each design alternative. There are several models and methods that may be used to estimate pollutant contributions and reductions, however it is important that the results are reported in the correct units (e.g. lbs/year, cf/year). Step 2: Estimate Capital Construction Cost. The source and representation of capital costs should be considered carefully. The best available sources should be used, which may include close-out budgets at the completion of a built project, construction contractor bids, line item budgets for recently completed projects nearby, and experienced cost-estimators with good track records. Estimates may also be derived based on County supplied estimates used to secure bonds from developers to ensure satisfactory completion of a project, engineering estimates, or other reputable source. Depending on the objectives, it may be more appropriate to report costs for the BMPs only, BMPs and conveyance only, or for the entire site. The level of cost detail is an important consideration as summary values that are lumped together may unintentionally embed portions of the project that are not stormwater related or relevant. While the ultimate costs can be collapsed, the raw data should provide enough detail so that relevant site categories can be included or excluded as appropriate. The year of reported dollars should be noted, as this will allow for adjustment of costs over time as the dollar loses value in real terms.
If comparing only the stormwater components of competing plans, one should consider what would take the BMPs place in its absence and also report that value, or subtract it to report the net capital cost, if appropriate for the analysis. In other words, permeable pavers may be used in a parking lot, providing the dual purpose of stormwater and transportation function. Without the use of permeable pavers
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however, the parking spaces would still need to provide the transportation function. Therefore, the ‘stormwater component’ of the permeable pavers would be the net difference between the paver scenario and the asphalt parking lot scenario. Similarly, if turf is to take the place of bioretention cells, this installation cost (which may be as high as $0.50/sf), should be accounted for if it is the ‘stormwater components’ that are of interest. Step 3: Estimate Life Cycle Costs.
a) Maintenance Costs. Local documentation tracking maintenance requirements over time can be a valuable source for estimating future costs, though it is often unavailable. In absence of this or other similar information, there are several publications that may aid with estimates. The Water and Environment Research Foundation (WERF) and Lampe, et. al. (2005) released a set of Whole Life Cost (WLC) spreadsheets to assist users in estimating capital costs, operations and maintenance and net present values for several BMPs including extended detention basins, retention ponds, swales, and permeable pavement. In 2009, this suite was expanded to include green roofs, large commercial cisterns, residential rain gardens, curb-contained bioretention, and In-curb planter vaults (WERF 2009a,b). Olson, Roesner, Urbonas, & MacKenzie (2010) also created a set of spreadsheet tools that include maintenance cost estimates.
The EPA (2005) and Center for Watershed Protection (1998) reported annual
maintenance costs as a percent of construction costs for several BMPs. They estimated maintenance costs for bioretention basins with underdrains and no pretreatment, retention basins, and dry ponds as a percent of construction cost were 5-7%, 3-6%, and ~1%, respectively. Weiss et. al. (2005, 2007) reported maintenance as percent of construction costs for rain gardens and dry ponds as 0.7-10.9% and 1.8-2.7%, respectively. SCLID (2008) reported permeable pavement as 3% of construction cost ($0.04/SF). In 2010, Erickson et al. conducted a survey of 38 cities and counties in Minnesota and Wisconsin and found that sediment removal was the most reported and costly maintenance activity with the median annualized costs below $1000 for most practices. The authors noted an economy of scale and reported that, as a general rule of thumb, maintenance costs as a percent of construction were 8% for $10k projects, 4% for $100k projects, and 2% for $500k projects.
b) Estimate Cost Additions or Savings. Savings may be realized from reduced maintenance of conventional materials (turf, asphalt), such as reduced fertilizer product purchase and application or mowing. Rainwater harvesting can be used to reduce purchases of municipally supplied water reducing initial installation costs and potentially even paying back the system in full over time. Forasté & Hirschman (2010) provided a methodology to quantify average annual volume reductions to meet SWM objectives, based on contributing roof areas and non-potable water demand estimates.
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c) Determine Discount Rate & Calculate Net Present Value. The selection of the discount rate is an important decision point. There is no single value that represents the correct rate, and there are several ways to calculate and select a discount rate. The rate selected may vary depending on the owner or company policy. For public federal projects that have constant dollar benefit cost analyses, OMB Circular No. A-94 (1992) specifies that net present value and other outcomes should be determined using a real discount rate of 7%. As most of the projects analyzed for this study were private developments, a rate of 8.5% return with an inflation rate of 3.0% yielding a real discount rate of 5.5% was selected and judged to be reasonable. This is also the default value used in WERF (2009a). An appropriate time period of analysis must also be established prior to calculating the net present value (NPV); in this study, a 50 year timeframe was chosen. The NPV is calculated as follows:
( )+=
t
nn
rRNPV
1 1
Where Rn is the net cost in year n; r is the discount rate; and t is the total number of years under consideration (Lasher 2008). Step 4: Calculate Cost Effectiveness. Three calculations are needed to determine costs on an annualized basis and the cost per unit.
a) Calculate Annuity factor. An annuity refers to a stream of payments over a specified period of time. The annuity factor is calculated as follows:
( )r
rA
t
rt+
−=
111
,
Where r is the discount rate and t is the number of years under consideration (Lial et al. 2004). For example, if a 5.5% discount rate is used over a 50 year period, At,r = 16.93.
b) Calculate ‘Equivalent Annual Cost’. Next, the Equivalent Annual Cost (EAC) is computed. The EAC is the cost of owning and operating an asset over its entire lifespan. It is calculated by dividing NPV by the annuity factor, as described in step 4a:
rtANPVEAC
,
=
Therefore, to calculate the EAC for a 50 year period of analysis using a discount rate of 5.5%, the NPV would be divided by 16.93 instead of 50 years.
c) Calculate Cost-effectiveness. Finally, by dividing the EAC by the quantity of pollutant removed per year (Pr), the cost effectiveness metric can be calculated as follows:
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rPEACivenessCostEffect =
Pr may represent the pounds of phosphorus removed per year, or the cubic feet
of retained runoff volume per year. Units are reported as $/lb/yr and $/cf/yr for each respectively. Case Study Application Project Description: Existing & Proposed Conditions The Union Rural Electric project is a commercial facility located in Marysville, Ohio, that needed to expand to meet its growing business needs. In 2008, the existing 9,000 SF of office space was renovated, and an additional 18,000 SF of office space added. The existing parking lot was removed, and replaced with increased capacity, with the expansion of the site built using LID principles.
The property was originally developed in the 1980’s, and designed only for
drainage function with the purpose of conveying runoff off-site through culverts and storm sewers. No water quality, detention, or retention facilities were incorporated at that time. The topography is relatively flat, sloping slightly away from the building, and the soils are comprised primarily of HSG C with clayey characteristics. Although the entire site is 9.5 acres, only the front portion was redeveloped, therefore only this 4.4 acre portion is considered here.
There was an existing ponding problem along the front yard turf areas. In
addition, the owners set a goal of achieving LEED Gold certification. Cardno JFNew, a full service design-build firm and CDS Associates, a civil engineering firm, utilized a series of three rain gardens, pervious concrete, grasspave, and a bioretention swale to help meet their redevelopment goals. The total impervious area was approximately 2.34 acres, or 53% of the total disturbed project area, and was primarily comprised of building rooftops. The project was built and completed in 2008.
In order to compare this LID project to an alternatively designed conventional
plan, a low cost design was developed in a manner that was culturally common to the locality as confirmed with aerial images and an Engineer with the City. Asphalt parking bays in place of pervious concrete, turf vegetation in place of bioretention and rain garden areas were selected as surface covers, and a detention basin was used to limit peak flows.
The primary stormwater management functions of the conventional plan are
conveyance of runoff generated from hard packed surfaces in a series of storm drain pipes, and maintenance of peak flow rates using a detention pond, which required additional land area to accommodate. In order to provide an ‘apples to apples’ comparison, the stormwater facilities of the conventional plan were designed such that the 2 and 10 year storm peak flow rates were less than or equal to pre-development (greenfield) rates, as is common with many stormwater regulations and design approaches. At the time, there were no Water Quality ordinances in the
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locality, so a detention basin – that is not normally specified for nutrient or volume reduction - would have satisfied current regulations. It would not however meet LEED WQ SS Credit 6.2. Each plan layout is presented on the following page in Figure 2. Step 1: Measure Stormwater Performance of URE. The TR-20 method within HydroCad was used to model hydrologic responses during the 1” rainfall, 1 year, 2 year, 10 year, and 100 year recurrence interval 24-hour storm events. The LID plan – as designed and built – exhibited 2 and 10 year peak flows below greenfield conditions. The conventional plan was developed to match the 2 and 10 year peak flows of the greenfield condition, as a low cost design. See Table 1 for results. Table 1. Peak Flows for LID and Conventional plans Location: Marysville, Ohio
Pre-development Post Development Storm Event Discharge Greenfield
Condition No Controls LID
Design Conventional Design
WQv (1”) Peak Flow (cfs) 0.04 2.61 0.26 0.43 Volume (Ac-ft) 0.016 0.13 0.01 0.10 2-yr (2.6”) Peak Flow (cfs) 2.55 11.62 1.71 2.58 Volume (Ac-ft) 0.27 0.57 0.08 0.53 100 yr (3.8”) Peak Flow (cfs) 5.60 18.93 2.94 5.68 Volume (Ac-ft) 0.57 0.95 0.14 0.89
The volume from the 1” storm is nearly fully retained in both the LID plan
and under greenfield conditions as modeled, though caution should be used, as TR-20 has been shown to be less reliable for these small storms events. While the 1 year storm was not a criterion for either plan, the difference in runoff volumes and peak flows between the two are significant, as evidenced by the overlapping hydrographs in Figure 3 below.
The Runoff Reduction Method (RRM) was utilized in this study to compute
annual total load nutrient reductions. The method assumes treatment of the first 1 inch of rainfall from the contributing drainage area and utilized research from the National Pollutant Removal Performance Database (CWP 2007) and other sources to estimate percent removal and average annual volume reduction rates for various BMPs (Hirschman, Collins & Schueler 2008). It should be noted that there have been variable BMP removal rate results and uncertainties reported, discussed in both the RRM Technical Memorandum and the BMP Database report (Geosyntec & WWE 2009). Annual nutrient loads were reduced by 23% and 78% for total phoshporus and by 20% and 78% for total nitrogen for the conventional and LID plans, respectively. The average annual volume reduction was also calculated using the RRM, to be consistent with the annual nutrient load removal computations, with the exception that the event mean concentration (EMC) term was removed and conversion factors were adjusted accordingly. Annual runoff volumes were reduced by 13% and 68% in the URE Conventional and LID plans, respectively compared to the post-construction plan with no SWM controls.
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Figure 2. URE Conventional and LID Site Plan Designs LID BUILT PLANCONVENTIONAL PLAN
LID
: IMPL
EM
EN
TA
TIO
N A
ND
EC
ON
OM
ICS
64
13
Figure 3. Hydrographs for LID, Conventional and Greenfield during 1-YR Event Step 2: Estimate Capital Construction Costs for URE. The capital construction costs for the LID plan were obtained from the design/build contractor that installed the stormwater facilities and include contractor expenses, labor, materials and landscaping. The capital costs of the conventional plan were derived using unit costs from the same source that were transferable (e.g. $/LF of drain pipe or $/inlet), and supplemented with additional sources, as needed. These included utilizing public records, including unit costs from a nearby recently completed commercial development site called “Crazy Burrito”, and portions of a public roadway expansion project neighboring the property. The total number of units for each line item were measured for each plan, and the unit costs applied. The results for each scenario are provided Table 2.
The combination of 32,000 SF of pervious concrete for the parking lot, and graspave for overflow parking and an access road, allowed for the replacement of almost one acre of impervious cover. Because the effective imperviousness of the site was reduce so dramatically, and large portions of the site store sizeable runoff volumes, including for large storm events, storm drain pipes were reduced by approximately 840 L.F., the number of grates and inlets by 10, curb and gutter by 1,084 L.F., and the 1 pond eliminated completely, with the associated land regained. Overall, the LID plan is approximately 6.9% less than the conventional plan. Step 3: Estimate Life Cycle Costs for URE. Several sources were utilized to develop the life cycle cost estimates. The basis of the LID estimates were initially derived using the WERF Whole Life Cost spreadsheets (2009), which partition maintenance into regular, correctirve, and infrequent maintenance activities. Where available, contractor supplied unit costs were used, such as mulch installation. The WERF (2009) spreadsheets were also used as an initial basis for estimating maintenance estimates for the detention basin in the conventional plan, and was suplemented with the EPA Pond Maintenance Guide (2004), Black and Veatch (2009), and Center for Neighborhood Technology (2010) resources to inform pond,
The 1 year storm event is often associated with channel forming influences and geomorphology concerns. This figure compares URE’s hydrologic response under greenfield, LID and conventional conditions. The difference in runoff volumes between the LID and conventional plans is highlighted in orange.
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turf, asphalt, curb and butter, drain inlet and pipe maintennace activity costs. These additional requirements include turf maintenance (e.g. mowing, fertilizing) only in the areas that replace bioretention areas, and crack sealing and coat resurfacing on the asphalt surfaces only in areas that replace pervious concrete and grasspave. In addition, repair of curb and gutters, and periodic cleaning and inspection of storm drain pipes and inlets are included for each plan. Additional narrative and a detailed line item breakdown are available in Draft Achieving More Cost-Effective Stormwater Management Plans using LID Practices. Step 4: Calculate Cost-effectiveness of URE. The results from the stormwater performance assessment and life cycle cost estimate are then combined in this section to create the cost-effectiveness metric. The storage unit costs, stormwater and drainage cost per treated impervious acre, and annualized cost per pound of phosphorus, nitrogen, and cubic feet of runoff volume reduced per year are calculated and included in Table 3 below. Storage volume, indicated in the first row, is the total fixed empty volume provided by all BMPs available to receive and store runoff. WQ
Table 2. Stormwater and Roadway Access Capital Costs
Site Work Category
Units Conventional Design
LID Design
Quantitative Difference Cost Difference
metric Cost Cost # Units $ Roadway & Access1 L.F. &
width $ 104,332 $ 120,000 Conv. Asphalt Surface, Base, &
subgrade compaction:@ $3.26/SF, Perv. Conc @ $3.75/SF
$ 15,668
Curb & Gutter L.F. $ 35,462 $ 19,310 1,084 L.F. less curb to encourage sheet flow to bioswale
- $ 16,332
Stormwater Drainage Pipes2
L.F. $ 71,699 $ 34,502 840 L.F. less storm drain pipe@ $27/LF for 12”, $38/LF for 18” and $ 45 /LF for 24”; $3.01/LF for gravel bed
- $ 37,448
Stormwater Structures (grates & inlets)
# grates, drop inlets
$ 28,600 $ 6,600 4 less grates, 6 less drop inlets @ $2,200 each
- $ 22,000
Stormwater Management (SWM ponds, bio cells & swales w/o plants
# ponds & size, risers
$ 58,082 $ 90,179 Eliminated basin of 37,667 CF; added 3 rain gardens & bio-sale @$8.17/SF avg. Includes oversight, landscaping, materials, labor
- $ 32,097
Landscaping3 SF $ 4,818 $ 11,651 Turf vs bioretention plants $ 6,833 Total Stormwater, landscaping & Roadway Costs
$ $ 302,992 $ 281,990 -6.9% - $ 21,001
1 Conventional pavement costs from City of Marysville US 36 roadway expansion project public records. Uit costs include: $ 1.00/SY for subgrade compaction, $ 135/CY for Asphalt Concrete(AC) aggregate base (6”), $140/CY for Ac surface course(1.5”). Original Asphalt Concrete Intermediate course (1.5”) and Agggregate base (6”) both excluded from URE conv. Paving costs to more closely match URE construction documents asphalt detail. Pervious concrete unit cost may be lower than would normally be expected as supplier /contractor may have provided close to at-cost. 2Underdain costs reflected in Stormwater Management category for LID site. City of Marysville public records for Crazy Burrito Commercial project used for cost basis to estimate Detention Basin, stormwater drainage and structure SWM costs for URE. 3Landscaping costs only reflect areas where rain garden and bioretention plants were used in the place of Turf. Sod costs (@$0.5/sf).
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Volume retained, in the last row, is the total volume of runoff that is retained by the installed BMPs on average every year. The final three rows in Table 3 divide the equivalent annual cost (EAC) by one year of pollutant load removed or volume reduced to achieve $/lb/yr and $/cf/yr values, respectively. Table 3. Measurement and Comparison of SWM Plan Cost-Effectiveness for URE
Pollutant Conventional Design
LID Design Difference
Cost-Effective Ratio
Annual $ /(unit) $/(unit) LID-conv Conv/LID
1st year Storage unit cost ($/cf)1 $ 4.20 $ 2.94 - $1.26 1.4 Stormwater & drainage costs / treated impervious acre ($/imp. ac.)2
$ 67,684 $ 58,709 - $ 8,975 1.2
Annual
TP removed (lbs/yr)3 $ 13,548 $ 3,516 - $ 10,031 3.9 TN removed (lbs/yr) 3 $ 2,230 $ 489 - $ 1,741 4.6 WQv volume retained (cf/yr) 3 $ 0.41 $ 0.07 - $ 0.34 6.2
1First year conventional storage refers to capacity of detention pond, not permanent pool. BMP, storm drain pipe, and inlet costs included. Additional pervious pavement and landscaping costs as well as avoided costs included in LID option and used as cost basis for all metrics in this table. 2Includes stormwater BMPs, storm drain pipes and inlets. Pervious concrete included as “treated impervious acre”. If quantified for BMP only, conv. Is $ 24,821/imp. ac. And LID is $ 48,154/imp. ac. for bioretention & additional pervious concrete. 3Equivalent Annual costs represent NVP over 50 years using discount rate of 5.5%; costs include storm drain pipes, inlets, BMPs and all maintenance costs; additional and avoided costs included in LID option.
The LID storage unit costs, which include stormwater facilities, drainage
pipes and inlets, additional cost for pervious concrete and landscaping, and avoided costs of curbing are approximately 30% lower than the conventional plan at $2.94/cf. Coupling the greater pollutant load removal and volume retention performance of the LID plan with its lower construction costs, creates a plan that is four to six time more cost effective than the conventional plan. In other words, the LID plan has a far greater pollutant removal per dollar capacity over the conventional plan. Results and key Findings Capital Cost Comparisons. In addition to URE and three additional case studies that were analyzed in detail to assess and compare the cost effectiveness of the LID to conventional plans, four more case studies were analyzed to compare capital construction costs only. A summary of these eight (8) case studies are provided in Table 4 below.
In all eight cases, the capital costs of the LID plan were comparable or much lower than the conventional plan. In one case, capital costs were higher. This result matches those of previous studies (MacMullan & Reich 2007, ECONorthwest 2007,
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U.S. EPA 2007). Reduction in storm drain pipes, inlets, impervious materials, and site preparation costs were frequently the source of savings.
Table 4. Site Development Capital Cost comparison of Conventional and LID plans.
Project Site Development Capital Costs SWM & Conveyance
as percent of Total Project Cost1
Difference Name State Conventional LID ($) ($) (%) Union Rural Electric2 OH $ 302,992 $ 281,990 -$ 21,002 - 7% n/a
Buckingham VA $ 1,499,745 $1,487,582 -$12,163 - 1% 1.6% Greenland Meadows2 NH $ 2,751,800 $1,008,800 -$1,743,000 - 63% n/a
Boulder Hills NH $ 789,300 $ 740,300 -$49,000 - 6% 1.5%
Kosair2 KY $ 143,299 $ 141,584 -$ 1,715 - 1% n/a
Ridgefield NC $ 2,502,606 $ 938,243 -$1,564,363 - 63% n/a
Lakeview Ave. MA $ 182,813 $ 160,668 -$22,145 - 12% n/a
Metcalf KS $ 2,937,818 $3,032,710 -$94,892 3% 0.9%
Total Project Average -19% 1Percent of Total project Cost represents LID option 2Stormwater BMP, conveyance, and additional roadway costs only; URE also includes curb and gutter and landscaping; Kosair also includes site prep and clearing. Cost Effectiveness Results of Case Studies. The four detailed case studies that compare conventional design to LID design in this study found clear and consistent differences between the cost-effectiveness of each plan. When LID controls were incorporated into each of the plans analyzed, replacing the conventional controls for an ‘apples-to-apples’ comparison, the LID plan proved far more cost-effective at removing pollutant loads and retaining runoff volumes. Table 5 summarizes the results for all four case studies.
The third and fourth columns in Table 5 provide the final cost-effectiveness values for each of the four case studies, representing annualized cost per pound of TP removed and cubic feet of runoff volume reduced per year. These values were derived by following the 4 step process described in this paper. The final column on the right is simply a ratio – calculated by dividing the conventional cost-effectiveness value by the LID value – to compare the relative cost-effectiveness between the two competing plans. The results indicate that the LID designs assessed here are from four to six times more cost-effective, on average, than the comparable conventional designs when environmental performance is factored into the cost analysis. This finding matches that by Traver as presented in his testimony to Congress: “From an engineering perspective they [LID practices] are the most cost effective and sustainable approach in mitigating the effects of urban stormwater runoff.” (2009).
Comparing Storage Unit Costs to Long Term Volume Reduction Costs. To better understand the mechanism behind this better performance, the long term
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annual cost per volume of runoff retained was plotted against BMP cost per unit of storage for each LID and conventional plan in Figure 4 below. As discussed in previous sections, capital cost per unit of storage volume is useful for budget planning purposes, but does not link initial installation costs to performance or consider long term costs and savings. This plot provides a comparison of the two.
Table 5. Comparison of SWM BMP and Conveyance (e.g. pipes) Cost- Effectiveness
TP ($/lb/yr) $13,548 $3,516 3.9Volume ($/cf/yr) $0.41 $0.07 6.2
Buckingham TP ($/lb/yr) $8,207 $1,174 7.0Volume ($/cf/yr) $0.25 $0.03 8.2
Kosair TP ($/lb/yr) $3,617 $1,648 2.2Volume ($/cf/yr) $0.11 $0.04 2.7
Metcalf TP ($/lb/yr) $15,457 $4,000 3.9Volume ($/cf/yr) $0.92 $0.20 4.6
Median TP Removal $10,877.50 $2,582.00 4.2 Volume Reduction $0.33 $0.06 6.0
Note: Costs represent stormwater BMP, s torm drain pipe, inlet l i fe cycle costs on an Equiva lent Annual Cost (EAC) bas is . Avoided and additional costs are included in LID.
Union Rural Electric
Cost-Effectiveness ratio (Conv/LID)
LID ConventionalPollutantProject
$0.01
$0.10
$1.00
$0 $2 $4 $6 $8 $10 $12Long
Ter
m V
olum
e Re
duct
ion
Cost
s ($/
cf/y
ear)
Storage Volume Installation Costs ($/cf)
Comparison between LID and Conventional Volume Reduction & Volume Installation Costs
Less Cost-
Effective
More Cost-
Effective
Figure 4. BMP Long Term Volume Reduction vs. Storage Volume Installation Cost
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The long term volume reduction costs for all four LID projects are below those of their comparative conventional plans. The LID plans average $0.085/cf/year, while the conventional plans average $0.42/cf/year. The primary factor underlying this six-fold improved cost-effectiveness of LID over conventional methods is its superior ability to retain stormwater and reduce runoff volumes at a comparable or lower cost. This plot also shows that while one BMP may have a lower construction cost per unit of storage volume over another, if the volume reduction performance is significantly better, then the cost per unit of volume reduced over time – or the cost-effectiveness of the practice - may actually be improved.
Discussion. All site design plans can vary depending on Designer and Owner experiences, preferences, and objectives. Many of the conventional plans presented here utilize a centralized dry detention basin approach, which has the primary purpose of limiting peak flows, but is not effective at removing nutrients or retaining volumes. They do assist many Engineers and Designers to meet peak flow based regulations, provide a low cost option, and are widely used however, which is why they were selected for the conventional plans here. If different conventional BMPs were selected – specifically those that were better at reducing runoff volumes - and the designs varied, results could vary.
BMP performance also likely varies over the long term, even with
maintenance, and so a decay of performance could occur, which is not represented here. The RRM utilizes average annual BMP volume reductions, and as such does not explicitly model antecedent moisture conditions, varying precipitation years, rainfall intensities, seasonal variations, routing of storms, complex treatment trains, and other factors, as some continuous simulation models may, which could affect results. Finally, results are sensitive to selection of discount rates.
To provide context for the results of this study and to ‘ground-truth’ the
values obtained, nine studies with a total of 42 projects, were identified to compare BMP costs to annual pollutant load reductions (38 for phosphorus removal and 15 for volume reduction). BMP construction costs per impervious acre ($/Imp. Ac.) were plotted against annual cost per pound of phosphorus removed ($/lb/yr). No clear pattern appeared to emerge between the two. Also, annual pollutant loads removed (lbs/yr) were plotted against Equivalent Annual Costs (annualized life cycle costs in $/yr) for the same 38 projects. A close relationship over a broad range was found (R2 = 0.91), however inefficiencies at any one scale were significant. This analysis can be found in the Draft Achieving More Cost-Effective Stormwater Management Plans using Low Impact Development (LID) Practices.
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U.S. EPA. 2004. Stormwater Pond & Wetland Maintenance Guidebook. Prepared by Center for Watershed Protection.
Water Environment Research Foundation (WERF). 2009a. Users Guide to the BMP and LID Whole Life Cost Models, Version 2.0. Document SW2R08.
Water Environment Research Foundation (WERF). 2009b. Whole Life Cost Spreadsheets
Water Street Studio. 2010. Bioretention Construction Documentation Detail. Weiss, P. T., J. S. Gulliver and A. J. Erickson. 2007. Cost and Pollutant Removal of
Storm-Water Treatment Practices. Journal of Water Resources Planning and Management, Vol. 133, N0.3.
Weiss, P. T., J. S. Gulliver, and A. J. Erickson. 2005. The Cost and Effectiveness of Stormwater Management Practices. Minnesota Department of Transportation Report 2005-23. http://www.cts.umn.edu/Publications/ResearchReports/reportdetail.html?id=1023.
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Economic and Adaptation Benefits of Low Impact Development
Robert M. Roseen, M.ASCE1, Todd V. Janeski2, Michael Simpson 3, James H. Houle4,Jeff Gunderson5, Thomas P. Ballestero, M.ASCE6,
1 Associate, Geosyntec Consultants, 289 Great Road, Acton, MA 01720, PH: (617)-992-9067 email: [email protected] 2 Environmental Scientist, Virginia Commonwealth University, Trani Center for Life Sciences, 1000 West Cary St, PO Box 843050, Richmond VA 23284-3050, PH: (804) 828.2858 Fax: (804)828.1622 e-mail: [email protected] 3 Chair, Environmental Studies Department, Antioch University New England, Keene, NH USA 03431 4 Program Manager, The UNH Stormwater Center, 35 Colovos Road, University of New Hampshire, Durham, NH 03824; PH 603-767-7091; FAX 603-862-3957; e-mail: [email protected]; web: www.unh.edu/unhsc/. 5 Professional Content Writer, Portland, Or 97209, Email: [email protected] 6 Associate Professor, Civil Engineering, P.E., Ph.D., P.H., C.G.W.P., P.G., Department of Civil Engineering; Principal Investigator, The UNH Stormwater Center, 35 Colovos Road, University of New Hampshire, Durham, NH 03824; PH 603-862-1405; FAX 603-862-3957; e-mail: [email protected]; web: www.unh.edu/unhsc/. Abstract
This paper presents a range of case studies illustrating the advantages of Low Impact Development (LID) in economic terms and metrics employed in municipal decisions making. The environmental and water quality benefits of LID are commonly known however, there are also considerable economic, infrastructure, and climate adaptation benefits being overlooked or ignored. Municipalities are faced with difficult economic choices from reduced capital budgets and increasing regulatory demands. As such, there is value in understanding the substantive economic benefits—for both construction budgets and project life-cycle costs—that are increasingly being realized by municipalities, commercial developers, and others when using Green Infrastructure (GI) for stormwater management. LID is often misperceived as only adding expense to a project; however, this perspective fails to acknowledge the broader benefits that can be observed in terms of whole project costs for new construction, and in some instances, increased life-cycle benefits. While individually GI elements may add upfront capital expense to a project, reductions can result from a decreased need for conventional drainage infrastructure. Cost benefits are not observed in comparison with projects with few to no stormwater controls, but
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rather for projects consistent with new state and federal permitting requirements that address volume and pollutant reduction.
Studies examined reported cost reductions for LID designs when compared with typical designs that relied heavily upon the use of drainage infrastructure. Project cost reductions were observed from 6% in residential developments to as high as 26% in commercial projects. Municipal use of GI reported cost reductions of 21% to as high as 44%. Of significant importance is the shifting of monies from infrastructure to jobs associated with the maintenance activities. From a sustainability perspective, a range of benefits includes reductions in flood damage and increased resiliency of drainage infrastructure; as well as reductions of 33 to 50% in energy demands for heating and cooling. Additional benefits observed included a 50% reduction in time to sale, and increased property values of 12-16%. Other benefits were incentives in the form of rebates, cost-sharing, and tax credits.
The use of LID planning and structural controls can contribute to building community resiliency in managing water resources and reducing the flood risk associated with current and projected changes in land use and climate. In one study, the implementation of LID practices reduced the number of culverts determined to be undersized by 29 to 100 percent for the 24 hr - 25 yr event. The marginal cost increase to replace such undersized culverts was also reduced by one-third. At the site scale, the use of LID as an adaptation measure can increase onsite storage of runoff compensating for increases in rainfall depths due to climate change. Onsite storage has additional benefits that increase resiliency such as increases in lag time and reducing and delaying the runoff peak discharge. Minimizing 2-year to 100-year floods with LID has the benefit to minimize stream instabilities that result from hydromodifications. Introduction
In addition to the commonly known environmental and water quality advantages, considerable economic, infrastructure, and adaptation planning benefits are also being realized through the incorporation of Low Impact Development (LID) and green infrastructure (GI) for stormwater management. LID- and GI-based strategies can also be used as a means for building community resiliency to changing climates in a water resources management context. However, because of the need for brevity, this compilation of case studies is limited to examining projects costs and does not address the important value of ecosystem services.
Runoff pollution occurs when rainwater and/or snowmelt moves across the landscape collecting contaminants, and discharges into a receiving water. This process is a significant source of impairment to the nation’s waterways. As the landscape transitions from natural conditions to higher percentages of impervious surfaces, effective strategies are necessary to capture and treat added stormwater volumes. Without effective strategies for managing stormwater, the list of impaired waters will continue to increase. Tremendous growth pressure has created the need
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for municipalities and watershed stakeholders to develop strategies for managing growth and maintaining watershed health. Most of the nation’s growing population is located in urban or coastal areas with highly vulnerable water resources (Woods and Poole 2010). Increasing population and changes to the urban landscape that increase the amount of impervious surfaces are directly related to the amount of nonpoint source pollution entering our watersheds, which negatively impacts aquatic resources (Caraco et al. 1998). Coastal communities reliant on the economic engines of viable shellfish fisheries, clean swimming beaches, or eco-tourism are also often negatively impacted by nonpoint source pollution (Bricker 2007). Many communities, at a time when municipal budgets are already strained, are burdened by the need to allocate capital resources towards addressing impaired water bodies (303d listings), separating combined sewers, implementing total maximum daily loads (TMDLs), managing municipal separate storm sewer systems (MS4s), or employing other environmental restoration programs. Stormwater is the primary source of the top five pollutants causing impairments of 303d- listed waters, which include pathogens, metals, nutrients, organic enrichment, and sediment (USEPA 2012). These pollutants are not effectively removed through conventional stormwater management approaches. A report examining urban stormwater management in the United States prepared by the National Research Council for the EPA detailed the failings of the current standard of practice for both stormwater management and regulatory permitting (NRC, 2009).
Traditional approaches to managing stormwater have focused on the application of drainage networks for diverting rainwater from residential or commercial areas with the purpose of improving safety and protecting the public from the effects of flooding. Capital and long-term operations costs are well understood and accepted with the usage of gray infrastructure. In most cases, protecting downstream ecological conditions was not considered. As the focus on protecting those resources increased, the design philosophy moved to capturing and treating smaller, more frequent storms and providing distributed storage throughout the built environment to reduce runoff volumes. LID is based on pre-development hydrology as the benchmark for runoff rate and volume goals for new projects. The use of LID reduces the need for larger treatment practices such as expensive gray infrastructure elements that concentrate stormwater flows and contaminants. LID takes into consideration the natural landscape to maximize onsite storage and infiltration in an effort to protect downstream aquatic habitat, maintain groundwater recharge, and reduce peak discharges and runoff volumes to receiving waters.
Combined sewer overflows (CSOs) represent major water quality threats to hundreds of U.S. cities and communities. Traditional CSO management involves the use of gray infrastructure for increasing storage and conveyance capacity. However, integrating LID into CSO mitigation is being used to help communities achieve CSO management at lower costs. Additional benefits include groundwater recharge, water quality improvements, and reduced treatment costs. LID can help minimize CSO events and the volume of contaminated flows by keeping runoff out of combined sewers (MacMullan 2007). Although communities rarely attempt to quantify and monetize the avoided treatment costs from the use of LID, the benefits of these
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practices to decrease the need for CSO storage and conveyance systems can be factored into any economic analyses (EPA 2007). In addition, LID can improve the ability for communities to become more resilient to changes in climate (Brekke, 2009, Binder, 2010). The economic impacts due to flooding can be staggering. Rainfall intensity, duration, and frequency are all predicted to change due to changes in climate (Frumhoff 2007). In some areas, the storm depth for today’s 100-yr storm may occur at a frequency of a 25-yr storm in the future (Stack 2005). The hydrological consequences will be manifested by more frequent flooding and increased damage to private property and critical infrastructure such as bridges, roads, and utilities. LID and GI provide distributed storage and infiltration throughout the watershed and has a positive cumulative effect on downstream areas by protecting those critical resources. As these practices are implemented, communities will realize avoided costs associated with the replacement and maintenance of infrastructure. Economic Background
LID can also have tremendous economic benefits that have been observed for nearly all development sectors including commercial, residential, and public. LID is commonly misperceived as only adding expense to a project; however, this perspective fails to acknowledge the broader capital benefits that can be observed in terms of whole project costs for new construction, and in some instances, increased life-cycle benefits. By combining both gray (traditional) and green (LID) approaches, the added expense of LID can be offset by the reductions in other traditional practices that rely heavily upon drainage infrastructure.
In the vast majority of cases, the U.S. Environmental Protection Agency (EPA) has found that implementing well-chosen LID practices reduced total project costs while also protecting and restoring water quality (USEPA 2007). Specifically, utilizing LID can result in project cost savings by decreasing the amount of required, expensive, below-ground drainage infrastructure and reducing or eliminating the need for other stormwater management-related facilities.
Other benefits include reduction of land disturbance and resultant land clearing and site development preparation savings. A Maryland study by Clar (2003) detailed a number of cost saving benefits by redesigning a conventional subdivision with LID designs. This included eliminating two stormwater ponds (costing roughly $200,000), increasing the number of build-able lots (adding approximately $90,000 in value), and allowing a more undisturbed site design (reducing clearing costs by $160,000).
From a sustainability perspective, a range of benefits also includes savings associated with increased flood resiliency, reduction of flood damage to drainage infrastructure, and reduction in energy demands for heating and cooling. MacMullan (2007) reported natural vegetation and reduced pavement in a Davis, CA
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development using LID helped lower energy expenses by 33 to 50 percent compared to surrounding neighborhoods. Further economic incentives include the potential for higher property values and reduced permitting fees. A 184-lot LID subdivision was documented as less expensive to develop (average of $7,000 less per lot), sold faster (50% decrease in time to sale), and have higher property values (12-16%) as compared to lots in conventional subdivisions (Mohamed 2006).
Other planning tools include rebates, cost-sharing, tax credits, and floor to area ratio (FAR) incentives for utilizing LID. MacMullan (2010) reported that the City of Portland, OR has a Green Roof bonus that provides an additional three square feet of floor area for every one square foot of green roof, provided the green roof covers at least 60 percent. King County, WA pays 50 percent of the costs, up to $20,000, to builders who install green infrastructure. Similarly, Austin, Chicago, and Santa Monica provide discounts for homes that employ LID. Also, in New York City, a project can earn a one year tax credit up to $100,000 for inclusion of a green roof on 50 percent of the structure, and in Maryland, green building credits are being used to offset property taxes and can be carried ten years forward. Climate Background
The core principle of LID is the management of increased runoff typically through filtration and infiltration strategies to provide treatment and reduce runoff volumes. These measures will have similar affects for managing increased storm sizes associated with changing rainfall patterns resulting from climate change.
Since 1976, the National Weather Service’s Climate Prediction Center has documented a trend consisting of an increase in annual precipitation ranging from 0.3 to 1.5 inches per decade for most of the Midwestern and Eastern parts of the country (NOAA/NWS, 2012). An analysis of weather records for specific locales in New England from 1970 to 2000 shows there was a 20 to 28 percent increase in the average amount of rainfall in a twenty-four hour period (Stack et al., 2005; Simpson, 2012). Additionally, numerous researchers have indicated that with an increase in mean precipitation, there will be a disproportional increase in extreme precipitation events. (Hennessy et al. 1997; Zwiers and Kharin 1998; Groisman et al. 1999; Meehl et al. 2000; Semenov and Bengtsson 2002; Watterson and Dix 2003; Tebaldi et al. 2006). Examining river gauge data in New England, researchers have found that of the 15 largest flooding events since 1934, 11 occurred in the last 25 years, 10 in the last 15 years, and 7 in the last 5 years. (Scholz 2011).
Scientists have projected rainfall shifts in the Great Lakes states where total annual average precipitation levels may not change, but seasonal distribution of rainfall amounts will. These projections include increasing precipitation in the form of rainfall during winter seasons, but with summer months forecasted to experience decreasing rainfall. This region will also experience significant increases in the frequency and intensity of extreme precipitation events, especially under a higher emissions scenario (Kling et. al. 2003). In the region encompassing Maine to New
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Jersey- Pennsylvania, regional projections for precipitation show a similar response with a higher frequency of days with temperatures above 90°F, less winter precipitation falling as snow, and more rain precipitation. Additionally, projections call for an earlier spring snowmelt resulting in earlier peak river flows, with an increase in the frequency of intense storms and storms with greater amounts of precipitation (Union of Concerned Scientists 2007; Wake 2011).
Upgrading existing drainage systems is considered to be the most expensive means of accommodating increased peak flow resulting from climate change (Blanksby et. al. 2003). Alternative economical adaptation strategies include reducing peak flow through the application of LID (Coffman 2005), best management practices (BMPs) (Urbonas and Stahre 1993), sustainable urban drainage methods (Butler 2000), and smart growth lot design (Daniels, 2001).
Methodology
This study used a range of approaches to develop case study information, including a social science analysis of local municipal decision makers, engineering costing studies, and land use build-out projections.
Data development and analysis was conducted for the purpose of preparing cost estimates and cost-benefit analyses that compared conventional stormwater approaches to LID in the context of residential and commercial development, combined sewer overflow management, increasing levels of impervious cover (IC) and climate change. Direct interviews, market surveys, and focus groups were conducted with local municipal officials, professional educational outreach partners, and engineering professionals to capture the breadth of unpublished information for quantifying the cost benefits of LID and GI. Information for commercial and residential case studies was developed by engineering design consultants who developed and permitted each of the projects. In both instances, each project had a parallel conventional design that had been proposed initially, contested, and followed by an LID design that was ultimately approved and constructed. The design firms then performed an independent engineering costing analysis for each alternative using standard estimating approaches for project bidding based on materials quantities and labor to install.
In order to develop engineering costing analyses, the firms of SFC Engineering Partnership and Tetra-Tech Rizzo prepared alternate designs for the Boulder Hills (residential) and Greenland Meadows (commercial) projects, respectively. For both projects, hydrologic models typical of standard civil engineering were used for the site design and permitting of the project. Recognizing the high degree of error or uncertainty inherent in many aspects of stormwater modeling, the authors are cognizant of the limitations of event-based models, which are not intended to be reflective of the highest level of accuracy that is possible with continuous simulation, but rather, are indicative of engineering tools common to the permitting and design process. Modeling of stormwater runoff was performed using
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the Natural Resource Conservation Service (NRCS) TR-55 Curve Number (CN) method (NRCS 1986). The CN method was selected for runoff computation because it is commonly-used, well-validated, and permits transparency-enabled facile diagnosis of the various sensitivities that can impact results. The 24-hour rainfall runoff was calculated for the one-inch water quality event, and the two-year, 25-year, and 100-year storm events using a Type III rainfall distribution with historic and revised rainfall data sets. Revised precipitation data reflecting recent climate change through 2010 was used from the Northeast Regional Climate Center.
For the Oyster River watershed culvert vulnerability analysis, researchers utilized a geographic information system (GIS)-based watershed modeling approach to examine the hydrological impact on existing culvert infrastructure of several climate change and land use scenarios. Field data was collected on culvert capacity, vegetation cover, slope, soils, permeability, roads, and land use. The project applied standard hydrological assessment methods to estimate runoff volumes and peak flows under current and projected future precipitation and land-use patterns (Stack et al. 2010; Durrans 2003). A curve number reduction method for LID was also used (McCuen 1983; MDE 2008). Because there are a limitless variety of LID system applications in a design context, the CN analysis performed here is based on providing a one-inch WQV volume for all impervious surfaces. For the CN analysis, the practice type is unimportant, but storage volume is critical. This analysis applied the use of a variation of bioretention and porous pavements for design scenarios (Stack et al 2010). Individual culverts were ranked according to vulnerability and potential hazard to the community with a prioritized schedule for guiding the planning of LID ordinances and culvert upgrades. Results and Discussion Economics. This section details the cost benefits of LID for the commercial, residential, and municipal case studies. The first two case studies show how utilizing an LID approach for site drainage engineering, specifically with porous asphalt, led to more cost-effective site and stormwater management designs; followed by a bioretention retrofit.
Residential Development (Boulder Hills): In 2009, a residential development was installed consisting of a 14-acre, 24-unit condominium community in Pelham, New Hampshire. The initial conventional design proposal had substantial wetland impacts, a conventional design with asphalt paving, and typical drainage (curbing, catch-basins, stormwater ponds, outlet structures). A second design was proposed that used widespread infiltration and filtration on the site’s extensive upland sandy soils, and included rooftop infiltration trenches, porous asphalt driveways, sidewalks, and New Hampshire’s first porous asphalt road. Table 1 shows construction estimate cost comparisons between both options. The LID option had a 6 percent reduction in site development expenses ($49,000 less) as compared to the conventional option. Although materials for the porous asphalt were more expensive than traditional
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asphalt, cost reductions in drainage infrastructure, site clearing, and erosion control were achieved.
Table 1: Comparison of Material Unit Costs
Item Conventional LID Difference Site preparation $23,200 $18,000 -$5,200 Temp Erosion Control $5,800 $3,800 -$2,035 Drainage $92,400 $20,100 -$72,273 Roadway $82,000 $128,000 $45,918 Driveways $19,700 $30,100 $10,386 Curbing $6,500 $0 -$6,464 Perm. Erosion Control $70,000 $50,600 -$19,460 Additional Items $489,700 $489,700 $0 Buildings $3,600,000 $3,600,000 $0 Project Total $4,389,000 $4,340,300 -$49,000
Commercial Development (Greenland Meadows): In 2008, a large commercial retail facility was constructed consisting of three franchise stores (home improvement, department, and grocery) and an estimated usage of 10,000 vehicles per day. The 38.4-acre retail shopping center located in Greenland, New Hampshire included a 4.5-acre porous asphalt installation (largest in Northeast), subsurface gravel wetland, and storage of rooftop runoff. Due to limited permeability of the underlying clay soils, a stormwater management plan had to incorporate stormwater quantity attenuation, storage, conveyance, and treatment. Table 2 presents total construction cost estimates for two options. For the LID option, there were reductions of $71,000 for earthwork and $1,743,000 for stormwater management costs due to a lower reliance upon conventional infrastructure. Table 3 details pipe quantities for the two options. The LID design required nearly 10,500 less linear feet of 36”-48” diameter pipe than the conventional design. A crushed stone reservoir within the pavement system was used in place of the pipe. The LID option was calculated at $930,000 less compared to the conventional option, a 26 percent reduction in site development expenses.
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Table 2: Comparison of Material Unit Costs
Item Conventional Option
LID Option
Cost Difference
Mobilization / Demolition $555,500 $555,500 $0Site Preparation $167,000 $167,000 $0Sediment / Erosion Control $378,000 $378,000 $0Earthwork $2,174,500 $2,103,500 -$71,000Paving $1,843,500 $2,727,500 $884,000Stormwater Management $2,751,800 $1,008,800 $1,743,000Additional Work-related Activity (utilities, lighting, water & sanitary sewer service, fencing, landscaping, etc.)
$2,720,000 $2,720,000 $0
PROJECT TOTAL $10,590,300 $9,660,300 -$930,000* Costs are engineering estimates and do not represent actual contractor
Table 3: Conventional and LID Options Piping
Design Function HDPE Pipe Size Quantity Cost (in) (linear feet)
Conventional Distribution 6 to 30 9,680 $298,340 Detention 36 and 48 20,800 $1,356,800
LID Distribution 4 to 36 19,970 $457,780 Detention* -- 0 $0
*Costs associated with detention in the LID option were accounted for under “earthwork” in Table 2.
Parking Lot Bioretention Retrofit: A bioretention retrofit was performed at
the Univeristy of New Hampshire campus. In certain instances using existing resources, simple retrofits can be performed at minimal expense. This retrofit involved the installation of a bioretention system within the vegetated median in the parking lot and subsequently connecting the system directly to adjacent drainage infrastructure. Facilities operations can often provide both labor and equipment for retrofitting existing infrastructure. In this instance, and many others with municipal staff, retrofit expenses were limited to design and materials costs only, while installation expenses for labor, equipment, and some infrastructure can be potentially avoided. Total project cost per acre of impervious cover was $14,000. With labor and install provided, costs were limited to materials and plantings at $5,500 per acre of impervious cover.
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Conventional CSO Abatement: Conventional storage, pumping, and treatment are extremely effective yet resource intensive for both construction and long-term operations. The Narragansett Bay Commission (NBC) in Providence, Rhode Island, under EPA direction, initiated a phased CSO Abatement Plan for mitigating CSOs and protecting the Narragansett Bay and the region’s urban rivers. Phase I of the project included a $365 million, three-mile, 30-foot diameter deep rock tunnel with an estimated 62 million gallons of capacity for reducing overflow volumes by approximately 40 percent. The associated operational and maintenance costs of Phase I are $1 million per every one billion gallons of stormwater and sewage flow, or $1 for every 1000 gallons (Brueckner 2009). Phase II of the CSO abatement plan includes two near-surface interceptors for conveying flow at an estimated capital costs of $250 million. Green Infrastructure and Municipal CSO Management.
Portland Oregon: The City of Portland, Oregon is considered by many to be a national leader in the implementation of innovative stormwater management strategies and designs. In June of 2000, the city was faced with the need to upgrade an undersized sewer pipe system in the Brooklyn Creek Basin, extending 2.3 square miles from Mt. Tabor to the Willamette River. The city considered a new separated stormwater collection system at a cost of $144 million (2009 dollars), using gray infrastructure to support undersized pipes in this basin. A second plan was developed and ultimately chosen that included a basin redesign using a combined gray infrastructure and LID approach. Including $11 million allocated for green solutions, the cost estimate for this integrated approach was $81 million, a 44 percent capital savings of $63 million (Portland 2009). Responding to federal and state requirements, including Clean Water Act stipulations, the city constructed two CSO tunnels and a new pump station in order to significantly reduce CSO events. However, more projects and programs were needed for providing additional CSO mitigation. The city considered a range of stormwater management solutions (Table 4) including LID strategies, evaluating options based on cumulative capital costs, marginal costs for gallons removed, and cumulative volume that could be removed. Cost-effectiveness was determined by an inflection point that compared costs to stormwater volume that could be diverted. Projects/programs costing at or below this marginal cost (determined to be about $4 per gallon), were recommended for implementation for long-term CSO control (first 7 listed in Table 2). As shown, 5 of these programs included LID strategies.
The $4 per gallon marginal cost is also considered as the avoidance cost associated with facilities maintenance and operations for constructing a larger CSO tunnel. In life-cycle cost analyses, this “savings” can reduce capital costs of other LID facilities that the city builds for objectives other than CSO control (e.g. water quality improvements, basement flooding relief), but still removes stormwater from entering the CSO tunnels (Owen 2009).
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Table 4: CSO Control Alternatives Costing for Portland, OR
Project/Program Marginal Cost ($/Gallon)
Cumulative Volume Removed (MG)
Cumulative Capital Cost
Extended Downspout Disconnection Program (can include LID) $0.89 7.45 $6,633,000
School Disconnection* $1.10 9.22 $8,587,000
Church Disconnection* $2.12 10.18 $10,618,000
Beech-Essex Sewer Separation $2.78 11.58 $14,507,000
ES Curb Extensions (LID) $2.87 15.87 $26,830,000
Tanner Phase 3 Sewer Separation $3.47 18.97 $37,598,000
ES Roof & Parking IC (LID) $4.08 36.61 $109,645,000
NWN Pre-design – Tanner North Sewer Separation $5.12 36.83 $110,772,000
Carolina Stream & Storm Separation $5.21 37.85 $116,090,000
NWN Pre-design – Tanner South Sewer Separation $6.16 38.11 $117,693,000
NWN Pre-design – Tanner Central Sewer Separation $7.60 38.14 $117,962,000
NWN Pre-design – Nicolai/Outfall Sewer Separation $11.76 38.68 $124,283,000
NWN Pre-design – Nicolai/Outfall 13 Sewer Separation $12.04 39.36 $132,500,000
Green Roof Legacy Project (LID) $13.65 40.4 $146,679,000
NWN Pre-design – Nicolai/Outfall 15 Sewer Separation $17.98 40.77 $153,225,000
Holladay Sewer Separation $20.94 41.45 $167,585,000
NWN Pre-design – Balch Neighborhood Sewer Separation $55.06 41.59 $175,249,000
NWN Pre-design – Balch/Forest Park Storm Separation $93.82 41.72 $187,275,000
* Church and School Disconnection programs assumed downspout disconnection and drywells would remove this stormwater volume. The former is an LID method.
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Kansas City, Missouri: Challenged by the significant expense of CSO reduction using gray infrastructure, the City of Kansas City (KC), Missouri began a feasibility assessment of integrating green solutions as part of a National Demonstration Project funded by USEPA. Under a USEPA mandate, the cities nationwide are required to update their networks of aging sewer infrastructure in order to address overflows from combined and separate sewer systems. For KC, this amounts to 6.4 billion gallons annually. The original, estimated costs associated with overhauling KC’s total sewer system were $2.4 billion dollars. Yearly operations and maintenance costs (O&M) of the upgrade were estimated at $33 million. In considering cost-effective alternatives, the city explored the feasibility of incorporating LID strategies in combination with gray infrastructure improvements and subsequently submitted a new plan that proposed a total of $80 million in green solutions programs. Based on city analyses, it was determined that replacing gray infrastructure with green solutions would be cost-effective in portions of the 744-acre Middle Blue River Basin (MBRB). Two CSO storage tanks could be eliminated by the use of distributed storage using LID without increasing costs or reducing CSO control performance (Leeds 2009). Compared to an estimated $54 million gray infrastructure design capable of providing 3 MG of storage, a revised MBRB Plan consisting of gray infrastructure and LID with distributed storage of at least 3.5 MG was estimated at $35 million – a 35 percent reduction ($19 million less) in estimated capital costs as compared to the original gray infrastructure plan.
Chicago, Illinois: The City of Chicago has been focused on the use of LID
for reducing combined sewer system volumes. The city is committed to managing stormwater more sustainably, and has implemented LID initiatives such as the Chicago Green Alley Program for facilitating infiltration, improving water quality, and diverting water from the combined sewer system, thus reducing energy demands associated with pumping and treating sewage. LID and other BMP measures are also used for limiting stormwater volumes and reducing the frequency and intensity of CSO events. In 2009, based on City of Chicago estimates, BMP designs (including LID strategies) effectively diverted 70,182,000 gallons of stormwater from the city’s combined system.
New York City, New York: New York City has furthered the analysis in their
2010 Green Infrastructure Plan, which details a range of operations and maintenance benefits, including sustainability metrics. A very significant element is the extension of economic benefits in terms of lower O&M costs and a greater distribution of costs towards jobs, resulting in job creation. The plan also details reducing energy costs, increasing property values, lowering O&M costs in terms of energy demand, improving air quality, and reducing CO2 production. This would be largely accomplished by the capture and infiltration of one-inch of rainfall on 10 percent of impervious cover in combined sewersheds by 2030. The City modeled CSO volume projections for both gray infrastructure and GI strategy. The GI strategy implemented over 20 years would reduce CSO volumes by nearly 2 billion gallons per year (bgy) as compared to the gray infrastructure approach (19.8 bgy vs. 17.9 bgy). The long-term capital costs associated with full implementation of the GI strategy are
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forecasted at 22 percent, or $1.5 billion, less compared to the gray infrastructure strategy over the next 20 years. In terms of a unit cost basis, the GI option is $0.45 per gallon vs. $0.62 per gallon for the gray strategy.
In addition, the Green Infrastructure Plan shows a greater distribution of funds
to support maintenance-related activities in the form of salaries and benefits. This is an important finding as job creation is one element of sustainability that is often overlooked. The NYCDEP also estimated a range of associated sustainability benefits including lower energy costs, reduced CO2, better air quality and increased property values. The total accumulated value of these benefits is projected from $139 to $418 million over 20-year implementation.
Climate Change. For many regions of North America, projections call for an increase in the depth, frequency and duration of precipitation events, which in turn can translate into significant environmental impacts to natural and human built systems (NRC 2001). Projected changes in climate and associated impacts through this century should be considered when planning for development and redevelopment. By adding distributed storage and infiltration throughout project sites, LID and GI can have a cumulative positive effect on a watershed and can be used as an adaptation tool for building resiliency to extreme events.
With Boulder Hills, LID planning and structural controls were used to minimize increases in runoff volumes due to development (Figure 1). In addition, this site can demonstrate impacts on stormwater runoff for both post-development and for increased storm depths under potential climate change scenarios. For the Boulder Hills site design, recharge volumes for pre-development and the LID design are very similar, whereas the conventional design demonstrates a tremendous increase in storm runoff volumes. For water quality volume (in most regions equivalent to the one-inch, 24 hour rainfall event), many LID designs yield no additional runoff, thus replicating pre-development conditions. This is significant because in the New Hampshire region, 92 percent of the storms are less than one-inch from which no runoff would be generated. For larger storms where runoff is observed, the volume retained from LID designs is actually greater than pre-development. This impact is most notable with increasing storm depth, and in part, is due to added infiltration and storage built into the LID landscape, as well as the tremendous lag time that occurs using porous pavements. The use of porous pavement systems adds substantial storage capacity because they are usually designed to serve for transportation functions (load capacity and resistance to frost depth in cold climate zones) as well as for stormwater management. This represents additional resiliency and explains why the peak flow rates and runoff volumes for the LID site are lower than pre-development conditions. Similar improvements could also be expected to a varying degree for higher density sites with similar system and site characteristics.
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Figure 1. Climate change impacts
Changes in climate and related impacts were analyzed with respect to stormwater conveyance infrastructure in the southern NH Oyster River watershed, to examine the relationship among land use impacts, a changing climate (higher frequency of larger precipitation events), and the use of LID as an adaptation tool to mitigate projected increased runoff (Stack et al 2010). Oyster River is a 19,857-acre watershed which includes portions of six townships and a population density of 304 persons per square mile (United States Census Bureau, 2010). Population growth, at 8.6 percent, had been vigorous for an 8-year period ending in 2008, equaling 10.8 percent per decade. This exceeds the growth rate through the 1990s of 0.8 percent per decade. Climate change scenarios were developed, which included costing estimates for upgrading conveyance systems to compensate for the changes in hydrology, and focused on the impacts to culvert sizing using climate change precipitation scenarios based upon the IPCC optimistic A1B and pessimistic A1Fi scenarios, named “Balanced Growth” and “Fossil Fuel Intensive Growth”, respectively. Culverts were determined to be undersized if the actual cross-sectional area of the culvert currently in place was less than the cross-sectional area modeled for a given scenario.
The baseline scenario indicated 5 percent of culverts are currently undersized for the amount of run-off generated by a 25-year, 24-hour rain event based on historic
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rainfall. When build-out is considered, and utilizing the precipitation amounts from the historic rainfall records, an additional 7 percent are undersized for the “most likely” 25-year, 24-hour event. A maximum of 35 percent of culverts are projected to be undersized under full-build-out, with no LID methods.
These culvert vulnerabilities are projected to increase with climate change.
The analysis, using an optimistic future scenario of higher rainfall (A1b), estimates that the “most likely” 24-hour, 25-year event for the mid-21st century will be 35 percent greater than the 24-hour, 25-year baseline precipitation event; the “most likely” 25-year more pessimistic future scenario of increase in rainfall (A1Fi) will be 64 percent greater than the 25-year baseline precipitation event.
The incorporation of LID under the more moderate modeled precipitation
amounts resulted in a 29 to 100 percent reduction in the number of culverts within the watershed that are undersized. However, for the more pessimistic A1Fi climate change model, the efficacy of LID in reducing the number of undersized culverts decreases. This becomes apparent when considering a static effective storage capacity of one inch was utilized when incorporating LID into the buildout scenario and storage capacity is exceeded as future climate change scenarios delivered progressively greater and greater precipitation. A marginal cost analysis was performed which detailed the increases in runoff from build-out by 22 percent per-culvert. With the use of LID, the marginal cost increased 14 percent, or a 33 percent reduction. Study findings indicated that a set of LID methods that is modest but achievable can mitigate the impacts of climate change and population growth. Summary and Conclusions
Numerous quantifiable economic benefits exist for the usage of LID and GI
strategies for both planning and implementation. Better education for the development and design communities can communicate a broader understanding of the range of benefits that are being observed nationally. Benefits include water quality and habitat protection, increased resiliency in the developed landscape, and the economics of water management. Economic benefits are realizable in both the short-term sense of project capital costs as well as in long-term sustainability metrics such as reduction of energy needs for heating and cooling, and lower O&M costs of municipal wastewater treatment including ecosystem services. Capital benefits are commonly observed as a result of an economy of high priced gray infrastructure in combination with the generous use of LID and GI techniques. Of significant value is the use of LID and GI as an adaptation measure to increase community resiliency in managing water resources and reducing the infrastructure and marginal costs due to increased runoff associated with current and projected changes in land use and climate.
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Table 5: Summary of Cost Analysis across Precipitation, Land-use and Antecedent Soil Conditions
Moisture Condition
Precipitation Scenario
Land-Use Scenario
Precipitation (in)
Undersized Culverts
Replacement Cost
Upgrade Cost
Marginal Cost
% Difference
Cost per Culvert
AMC II Baseline Current 5.4 4 16,900 24,600 7,800 46% 1,900
Build-Out 5.4 8 56,600 88,300 31,800 56% 4,000
LID 5.4 6 28,900 50,500 21,600 75% 3,600
A1b Current 6.9 9 75,700 101,200 25,600 34% 2,800
Build-Out 6.9 16 145,800 204,300 58,600 40% 3,700
LID 6.9 12 110,900 152,600 41,800 38% 3,500
A1fi Current 8.3 17 147,200 203,800 56,700 38% 3,300
Build-Out 8.3 19 171,600 234,400 62,900 37% 3,300
LID 8.3 18 160,700 222,300 61,600 38% 3,400
AMC III A1b Current 6.9 18 151,400 208,900 57,600 38% 3,200
Build-Out 6.9 20 175,800 239,500 63,800 36% 3,200
LID 6.9 19 165,000 227,400 62,500 38% 3,300
A1fi Current 8.3 22 191,900 273,200 81,400 42% 3,700
Build-Out 8.3 25 224,800 321,400 96,600 43% 3,900
LID 8.3 23 201,000 269,900 68,900 34% 3,000
+95% c.I.: 48% 3,565
Mean: 42% 3,317
-0.95 37% 3,070
Limitations and Future Research
There are many limitations to the use of LID, in particular the unrestrained use around sensitive resources. LID is not a replacement for natural resource protection and conservation. The use of LID can in some instances allow development access to areas that would have been prohibited by conventional designs due to standard regulatory and zoning limitations on volume and impervious cover.
Limitations of the project methodology include the usage of standard, non-controlled, design and permitting approaches as a data source. The limitations extend from the project structure which was to survey and compile existing projects and data sources nationally. This is distinct from controlled verifiable experimental design. Research grade experimental design would use the best available practices for hydrologic modeling, rather than tools common to design and permitting. The economic data was derived from design sources using professional judgment and standards in common practice. Engineering and project reports are referenced for documentation.
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Acknowledgements
The authors would like to acknowledge the Cooperative Center for Coastal and Estuarine Environmental Technologies (CICEET) and the National Oceanic and Atmospheric Agency (NOAA) for funding. Their support is gratefully acknowledged. The project success was based on the gracious participation of numerous partners: SFC Engineering Partnership, New Hampshire, Tetra Tech Rizzo, Manchester, New Hampshire, ECONorthwest, National Estuarine Research Reserve Coastal Training Program Coordinators from Old Woman Creek, Ohio, Wells, Maine, Great Bay, New Hampshire, Waquoit Bay, Massachusetts, the National Coordinator for Non-Point Source Education for Municipal Officials (NEMO), Maine NEMO Coordinator, Northland NEMO, Minnesota, Oregon and Washington Sea Grant Programs, Engineering Manager and Permits Manager from the Narragansett Bay Commission, Program Manager for Sustainable Stormwater Management at the Portland Bureau of Environmental Services, Engineering Services with the City of Portland Bureau of Environmental Services, the Sustainable Infrastructure Administrator for the City of Chicago Department of Water Management, Maine Department of Environmental Protection and the USEPA. References
Blanksby, J., Ashley, R., Saul, A., Cashman, A., Wright, G., Jack, L., and Fewtrell, L. (2003). "Scoping statement: Building knowledge for climate change adaptable urban drainage - addressing change in intensity, occurrence, and uncertainty of stormwater (Audacious). A project in the EPSRC/UKCIP Building Knowledge for a Changing Climate program." Engineering and Physical Sciences Research Council/United Kingdom Climate Impacts Program.
Bloom, A. J. (2010). Global Climate Change: Convergence of Disciplines., Sinaur Associates, Sunderland, MA.
Clar, M. (2003). "Case Study: Pembrooke Woods LID Development Residential Subdivision." Ecosite, Inc.
Coffman, L. (2005). Stormwater Management for Low Impact Development, CRC Press.
Daniels, T. (2001). "Smart Growth: A New American Approach to Regional Planning." Planning Practice and Research, 16, 271-279.
Durrans, S. (2003). Stormwater Conveyance Modeling and Design, 1st Edition, Haestad Methods Press, Waterbury, CT.
Frumhoff, P. C., McCarthy, J. J., Melillo, J. M., Moser, S. C., and Wuebbles, D. J. (2007). "Confronting climate change in the U.S. Northeast: science, impacts, and solutions." UCS Publications LA - English, Cambridge, ix + 145 pp.
Groisman, P. Y., Karl, T. R., Easterling, D. R., Knight, R. W., Jamason, P. F., Hennessy, K. J., Suppiah, R., Page, C. M., Wibig, J., Fortuniak, K., Razuvaev, V. N., Douglas, A., Førland, E., and Zhai, P.-M. (1999). "Changes in the Probability of Heavy Precipitation: Important Indicators of Climatic Change." Climatic Change, Springer Netherlands, 243-283.
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Hennessy, K. J., Gregory, J. M., and Mitchell, J. F. B. (1997). "Changes in daily precipitation under enhanced greenhouse conditions." Climate Dynamics, Springer Berlin / Heidelberg, 667-680.
Kling, G. W., Hayhoe, K., Johnson, L. B., Magnuson, J. J., Polasky, S., Robinson, S. K., Shuter, B. J., Wander, M. M., Wander, M. M., Wuebbles, D. J., and Zak, D. R. (2009). "Confronting Climate Change in the Great Lakes Region." The Ecological Society of America David Suzuki Foundation.
MacMullan, E. (2007). "Economics of LID." EcoNorthwest, Eugene, OR. Macmullan, E., and ECONorthwest. (2010) "Using Incentives to Promote Green
Stormwater Practices." Oregon Association of Clean Water Agencies Stormwater Summit.
McCuen, R., and Environment, M. D. o. (1983). "Changes in Runoff Curve Number Method."
MDE, and Environment), M. D. o. t. (2008). "Maryland Stormwater Design Manual, Supplement No. 1."
Meehl, G. (2007). "Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In Climate Change: The Physical Basis." Cambridge University Press, Cambridge GB and New York NY.
Meehl, G. A., Karl, T., Easterling, D. R., Changnon, S., Pielke, R., Changnon, D., Evans, J., Groisman, P. Y., Knutson, T. R., Kunkel, K. E., Mearns, L. O., Parmesan, C., Pulwarty, R., Root, T., Sylves, R. T., Whetton, P., and Zwiers, F. (2000). "An introduction to trends in extreme weather and climate events: Observations, socioeconomic impacts, terrestrial ecological impacts, and model projections." Bulletin of the American Meteorological Society, 81(3), 413-416.
Mohamed, R. (2006). "The Economics of Conservation Subdivisions - Price Premiums, Improvement Costs, and Absorption." Urban Affairs Review, 41(3), 376-399.
NASA. (Retrieved August 10, 2010). "Earth's 'Tipping Points': How Close Are We?" NOAA/NWS. (2012). "U.S. Temperature and Precipitation Trends." NOAA/NWS. NRC. (2001). "Climate Change Science: An Analysis of Some Key Questions."
Committee on the Science of Climate Change and National Academy Press, Washington D.C.
NRC. (2008). " Urban Stormwater Management in the United States." National Academy Press, Washington D.C.
NRCS. (1986). "Urban Hydrology for Small Watersheds TR-55." United States Department of Agriculture Natural Resources Conservation Service Conservation TR-55 Engineering Division.
Scholz, A., Roseen, R. M., Ballestero, T. P., and Wake, C. (2011). "Consequences Of Changing Climate And Land Use To 100-Year Flooding In The Lamprey River Watershed Of New Hampshire," MS in Water Resources Civil Engineering., University of New Hampshire, Durham, NH.
Semenov, V. A., and Bengtsson, L. (2002). "Secular trends in daily precipitation characteristics: greenhouse gas simulation with a coupled AOGCM." Climate Dynamics, 19(2), 123-140.
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Simpson, M. (2012). " Water from the Hills: The Need to Adapt is No." USEPA/New England Association of Environmental Biologists, Falmouth, MA.
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Stack, L, Simpson M.H. Crosslin T, Roseen R., Sowers D. and C. Lawson (2010). Oyster River Culvert Analysis. Final Project Report funded under a US EPA Climate Ready Estuaries Grant: 68 pp; can be retrieved at: http://www.prep.unh.edu/resources/pdf/oyster_river_culvert-prep-10.pdf
Tans, D. P., and Keeling, D. R. (2012). "Trends in Atmospheric Carbon Dioxide." NOAA/ESRL.
Tebaldi, C. (2004). "Hearing on Climate Change Impacts." U. S. Senate Committee on Commerce, Science and Transportation, Environmental and Societal Impacts Group National Center for Atmospheric Research (NCAR), Boulder, CO, 7.
UCS. (2007). "The Changing Northeast Climate: Our Choice, Our Legacy." Union of Concerned Scientists, Cambridge, MA.
USEPA. (2007). "Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices." EPA 841-F-07-006, United States Environmental Protection Agency Nonpoint Source Control Branch (4503T), Washington, DC 20460.
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detention for water quality, drainage, and CSO management, Prentice Hall. Wake, C., Burakowski, E., Douglas, E., Hayhoe, K., Kelsey, E., Stoner, A., and
Watson, W. (2011). "Climate Change in the Piscataqua/Great Bay Region: Past, Present and Future." Carbon Solutions New England, Durham, NH.
Watterson, I. G., and Dix, M. R. (2003). "Simulated changes due to global warming in daily precipitation means and extremes and their interpretation using the gamma distribution." J. Geophys. Res., 108(D13), 4379.
Zwiers, F. W., and Kharin, V. V. (1998). "Changes in the extremes of the climate simulated by CCC GCM2 under CO2 doubling." Journal of Climate, 11(9), 2200-22
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A Comparison of Maintenance Costs, Labor Demands, and System Performance for LID and Conventional Stormwater Management
James J. Houle1, Robert M. Roseen M.ASCE2, Thomas P. Ballestero M.ASCE3,
Timothy A. Puls4, James Sherrard5
1Program Manager, The UNH Stormwater Center, M.A.,CPSWQ. 35 Colovos Road, University of New Hampshire, Durham, NH 03824; PH603-862-1445; FAX 603-862-3957; e-mail: [email protected]; web:www.unh.edu/unhsc 2Director, The UNH Stormwater Center, Ph.D., Department of Civil Engineering, PH 603-862-4024; FAX 603-862-3957; e-mail: [email protected]; 3. Associate Professor, Civil Engineering, P.E., Ph.D., P.H., C.G.W.P., P.G., Department of Civil Engineering; Principal Investigator, The UNH Stormwater Center, PH 603-862-1405; FAX 603-862-3957; e-mail: [email protected]; 4 Facility Manager, The UNH Stormwater Center, B.S., EIT. PH 603-343-6672; FAX 603-862-3957; e-mail: [email protected]; 5James Sherrard, Engineering Technician, The UNH Stormwater Center, M.S. 35 Colovos Road, University of New Hampshire, Durham, NH 03824. Abstract
Maintenance of Low Impact Development (LID) systems represents a significant barrier to the acceptance of LID technologies. Despite the increasing use of LID over the past four decades, stormwater managers still have minimal documentation in regards to the frequency, intensity, and costs associated with LID operations and maintenance. Due to increasing requirements for more effective treatment of runoff and the proliferation of total maximum daily load (TMDL) requirements, there is greater need for more documented maintenance information for planning and implementation of stormwater management strategies.
This study examined 7 different types of stormwater treatment systems for the
first 2-4 years of operations and studied maintenance demands in the context of personnel hours, costs, and system pollutant removal. The systems were located at a field facility designed to distribute stormwater in parallel, with normalized watershed characteristics including pollutant loading, sizing, and rainfall. System maintenance demand was tracked for all systems and included labor, activities, maintenance type, and complexity. Annualized maintenance costs ranged from $2000/ha/yr for a vegetated swale to $7600/ha/yr for a retention pond. In terms of mass pollutant load reductions, marginal maintenance costs ranged from $4-$8 per kg/yr TSS removed for porous asphalt, a vegetated swale, bioretention, and a gravel wetland, to $11-$20 per kg/yr TSS removed for a retention pond, a detention pond, and a sand filter
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system. When nutrients such as nitrogen and phosphorus were considered, maintenance costs per kg/yr removed ranged from reasonable to cost prohibitive especially for systems with no nutrient removal mechanisms. As such, best management practices (BMPs) designed for targeting these pollutants should be selected carefully. The results of this study indicate that generally, LID systems, as compared to conventional systems, have lower marginal maintenance burdens (as measured by cost and personnel hours) and higher water quality treatment capabilities as a function of pollutant removal performance. Annual system maintenance expenditures equal total upfront capital costs after 4.5 years for retention ponds and after 20 years for the porous asphalt system. In general BMPs with higher percentages of periodic and predictive, or proactive maintenance activities have lower maintenance burdens than BMPs with incidences of reactive maintenance.
Introduction
The misunderstanding of inspection and maintenance expectations for Low
Impact Development (LID) systems have been one of the significant barriers to the acceptance of LID technologies. Most entities in charge of stormwater management systems over the past four decades generally have adopted maintenance plans or guidelines for conventional systems (curb, gutter, swale and pond), yet there is little documentation in terms of the frequency, intensity, and costs associated with LID maintenance operations required to meet system design objectives. With increasing requirements for more efficient stormwater management designs and the proliferation of total maximum daily load (TMDL) requirements, a greater amount of documented maintenance information is necessary to facilitate the implementation of more effective stormwater management strategies. Increased attention to pollutant loads, numerical goals, and non-degradation requirements has also created the need for more emphasis on best management practice (BMP) maintenance in order to meet permitting and reporting requirements (Erickson et al., 2010). Furthermore, as municipalities move to implement LID, managers need better information resources and methods to estimate an LID technique’s total costs, including maintenance. With more long-term LID maintenance costs available, cost estimations of this alternative will become easier to accomplish and more precise (Powell et al., 2005).
Traditionally, there has been significant resistance towards the acceptance and
adoption of LID designs due to the perception that these systems have substantial maintenance requirements, representing a significant cost burden to developers and site owners. In contrast to this perception, proponents regard LID designs as lower in maintenance compared to conventional stormwater controls (MacMullan 2007; Powell et al., 2005; EPA 2000). Additionally, LID technologies eliminate the need for costly maintenance contracts, typically requiring only routine landscape maintenance.
As an example of the available documentation directing LID maintenance
protocols, the Prince George’s County, Maryland Department of Environmental Resources Maintenance Schedule for Bioretention Areas (MDER, 2007),
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recommends a frequency and time of year for the maintenance of plants, soil, and the organic layer of bioretention systems. Likewise, the Washington State University Pierce County Extension Maintenance of Low Impact Development Facilities (WSU, 2007) provides maintenance schedules for bioretention and permeable paving areas, listing general maintenance activity recommendations including objectives. However, while recommending specific activities and frequencies associated with LID maintenance, these documents, like others, do not cover costs and are not based on empirical data or referable evidence in terms of studied LID maintenance activities for ensuring system functionality. While many stormwater management manuals have stated the importance and estimated frequency of maintenance for BMPs, few have documented the actual frequency and intensity of maintenance required to maintain a desired level of performance and efficiency (Erickson et al., 2010).
Weiss et al. (2005), in a study comparing the cost and effectiveness of several
common stormwater BMPs including LID designs (constructed wetlands, infiltration trenches, sand filters, bioinfiltration filters), found that no data was available that documented actual operation and maintenance (O&M) costs of existing BMPs. At best, the study found that available data consisted only of expected or predicted O&M costs of recently constructed BMP projects. Often times, estimated annual O&M costs are presented as a percentage of the total capital cost (Weiss et al., 2005) or as an annual percentage of capital costs (Narayanan and Pitt 2006). An example includes the USEPA’s (1999) annual O&M costs for a range of typical BMPs, expressed as a percentage of the construction cost.
In a study for advancing short and long-term maintenance considerations so as
to develop more realistic maintenance plans, Erickson et al. (2009) conducted a detailed municipal public works survey to identify and inventory stormwater BMP O&M efforts and costs. Results indicated that most (89%) cities perform routine maintenance once per year or less with staff-hours per year ranging from one to four hours for most stormwater BMPs, but significantly higher for rain gardens (one to sixteen hours per year) and wetlands (one to nine hours per year). In terms of costs, the study found that stormwater BMP maintenance expenses will roughly equal the construction cost (in constant dollars) after 10 years for a $10,000 installation and after 20 years for a $100,000 installation (2005 dollars).
In another effort towards better forecasting life-cycle project cost estimates of
different stormwater control alternatives, Narayanan and Pitt (2006) utilized maintenance cost data from the Southeastern Wisconsin Regional Planning Commission (SWRPC), which documented maintenance costs for a range of stormwater management devices, including LID. According to SWRPC figures, incremental average annual maintenance costs in 1989 dollars (over conventional pavement) for a permeable pavement parking lot was found to be $42/hectare ($17/acre) for vacuum cleaning, $20/hectare ($8/acre) for high-pressure jet hosing, and $25 per inspection. Likewise, annual SWRPC maintenance costs for infiltration trenches was found to be $92/100 hectare ($37/acre) for buffer strip mowing,
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$9690/hectare ($3920/acre) for general buffer strip lawn care, an $25/inspection plus $50/trench for program administration.
The University of New Hampshire Stormwater Center (UNHSC) has tested over 26 treatment strategies to date, logging all inspection hours and maintenance activities over the course of a 6-year study (2004-2010). For the purposes of this study, researchers have compiled data from UNHSC testing efforts of 7 different types of stormwater treatment systems including conventional stormwater BMPs such as ponds and a swale, as well as LID systems including bioretention, sand filter, gravel wetland, and porous pavement. Manufactured treatment devices were omitted from this study as many vendors and product providers offer comprehensive and detailed O&M information pertaining to their systems. Methodology
Site Design. The UNHSC site was designed to function as a series of uniformly sized, isolated, and parallel treatment systems with capacity for stormwater to be conveyed to each treatment device without significant transmission impacts from the distribution systems such as sedimentation. Rainfall-runoff is evenly divided at the headworks of the facility in a distribution box, designed with an elevated floor that is slightly higher than the outlet invert which allows for scouring across the floor and into the pipe network. Effluent from all of the treatment systems flows into a sampling gallery where system sampling and flow monitoring are centralized. The parallel configuration normalizes the treatment processes for event and watershed loading variations (all technologies receive the same influent hydrograph and water quality). This process is fully described in previous publications (Roseen, et al, 2009).
The stormwater treatment systems discussed in this paper include a vegetated
swale, retention pond, detention pond, sand filter, gravel wetland, three bioretention systems (averaged), and porous asphalt. The retention pond, after completion of 3 years of testing, was subsequently converted to the detention pond. All systems were designed according to specifications listed in Table 1. Detailed system information has also been previously published (Roseen, et al, 2009). The treatment strategies are all uniformly sized to treat the same peak flows and volumes, with equal capacity for conveying large flows. Design criteria were based on a rainfall frequency analysis to determine the 24 hour rainfall depth corresponding to a non-exceedance frequency of approximately 90%. For much of the northeast, daily total precipitation is less than 2.0-3.3 cm (0.78 – 1.3 inches) 90% of the time. The 90% criterion was selected here for its increasingly widespread usage, ability to generate economical sizing, and because water quality treatment with this guideline accounts for more than 90% of the annual runoff volume. Still, the veracity of this sizing concept will ultimately be evaluated. For Durham NH, 2.5 cm (one inch) or less of rainfall depth in one day occurs 92% of the time on the days in which measurable precipitation occurs. This data was derived from a NOAA precipitation gauge with 76 years of record that is within 1 km (0.62 miles) of the site.
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Table 1: List of normalized design criteria for systems in SI units and (English units)
Design specifications Value Unit Rainfall-runoff depth 25.4 (1.0) mm (in) Catchment Area 0.4 (1.0) hectares (acre) Treatment Peak Flow 2,450 (86,521) m³/day (ft³/day) 10-Year Peak Storm Flows 8,570 (302,647) m³/day (ft³/day) Treatment Volume 92 (3,249) m³ (ft³) Treatment Volume Drain Time 24-48 hours
Tracking and Calculation of Maintenance Costs. Stormwater treatment system designs and selection were primarily based on manuals from New York State (New York State Stormwater Management Design Manual, 2001), New Hampshire State (New Hampshire Department of Environmental Services, 1996), and the Federal Highway Administration (Brown, 1996, FHWA, 2002). The New York State manual includes operation, maintenance, and management inspection checklists for several BMPs. The manual guidelines were utilized on a monthly basis to track observations and maintenance activities for all BMPs discussed in this paper except for the porous asphalt (PA) system. The routine use of these forms helped to establish a framework for development of annual maintenance strategies. The PA maintenance activities were developed by adjusting typical maintenance activities for standard asphalt surfaces and applying them to porous systems. Maintenance tracking consisted of initial observations using inspection checklists, written documentation in field books, photo documentation of issues, and research staff assessments. Maintenance activity documentation included BMP name, activity description, labor hours to complete task, and name of staff members involved. Annual maintenance strategies were evaluated by quantifying hours spent, assessing difficulty of activities, and applying a standard cost structure.
To better illustrate costs and anticipate maintenance burdens, activities were
characterized into distinct categories. First, activities were assigned a maintenance complexity according to the following criteria (Erickson, et al 2010):
• Minimal – stormwater professional or consultant is seldom needed. • Simple – stormwater professional or consultant is occasionally needed. • Moderate – stormwater professional or consultant is needed approximately half the time. • Complicated – stormwater professional or consultant is always needed.
These categories allow more accurate cost predictions and provide insight into
the appropriate assignment of maintenance responsibilities. Minimal complexity activities can generally be performed by non-professionals and may include tasks such as mowing or slope seeding, whereas complicated activities may necessitate a
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design specification or the use of heavy equipment for requirements such as algae removal from wet pond.
Secondly, activities were categorized with respect to a maintenance approach.
The four basic maintenance approaches are found below (adapted from Debo, and Reese, 2003): • Reactive – complaint or emergency driven. • Periodic and Predictive – driven by inspections and standards embodied in an
O&M plan; can be calendar driven, known, or schedulable activities. • Proactive – adaptive and applied increasingly more as familiarity with the
system develops. Results and Discussion
Maintenance of stormwater management facilities is essential for ensuring that systems perform properly. This analysis relies on the assumption that routine maintenance and inspections of BMPs are performed as recommended. The development of an effective maintenance program takes time, and as with most systems it is not only specific to the individual BMP, but with many other variables including the overall design, system sizing, location, land use, and other watershed characteristics. In most cases, maintenance approaches are not static, but are instead adaptive as maintenance staff become familiar with the systems and are better able to plan for maintenance activities.
Research results indicate that maintenance activities are progressive:
maintenance tasks often start out as reactive (the most expensive category of maintenance), but subsequently evolve into periodic and proactive approaches. Figure 1 illustrates annual maintenance costs and personnel hours expended for each of the studied BMPs over time. After 2-3 years for all studied systems, maintenance efficiency developed into a predictable pattern with respect to annual costs. Research indicates that if maintenance activities are simple, then periodic and routine maintenance costs are kept at a minimum. Figure 2 illustrates that BMPs with higher percentages of periodic and predictive, or proactive maintenance activities have lower maintenance burdens than BMPs with incidences of reactive maintenance.
As depicted in Figures 1-2 and Table 2, maintenance burdens for vegetated filtration systems were generally less with respect to cost and personnel hours as compared to conventional BMPs such as ponds, with vegetated swales and sand filters as the exceptions. However, these results should be considered as conservative in that they document the most expensive period of maintenance that might be anticipated (the start up years). Barring unexpected maintenance issues or severe weather events that could occur beyond this study’s timeframe, the maintenance activities, approaches, and expenditures examined in this study generally became less intensive and diminished over time as maintenance familiarity increased. As an example, maintenance with respect to vegetated systems was found to require more attention
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during the first months and years of vegetation establishment. Additionally, while the activities associated with maintaining LID practices were found to be less expensive and more predictable than conventional systems, the scale, location, and nature of LID system maintenance requires different equipment (rakes and wheel barrels as opposed to vactor trucks) and will require new maintenance standards and strategies.
Figure 1: Maintenance Cost and personnel hours tracked per system per year
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Figure 2: Annualized maintenance costs per system per hectare of IC treated per maintenance activity classification Staff Hours. Personnel hours dedicated to maintenance for the stormwater treatment systems included in this study are displayed in Table 2. As shown, staff-hours per activity ranged from 14.8 to 74.1 hours per hectare of impervious cover (IC) treated per year (6 to 30 hours/acre/year). The sand filter system was found to require the most staff-hours, followed in declining sequence by the retention pond, detention pond, gravel wetland, bioretention, vegetated swale, and finally porous asphalt. These results were surprising as many of the conventional systems such as wet and dry ponds were found to carry the largest maintenance burdens. Maintenance routines for these systems required more tasks and included more reactive activities such as algae removal and outlet cleaning which tend to be more complex and incur higher costs. Table 2: Personnel hours per system per year per hectare of IC treated System Personnel (hrs/ha/year)
(hrs/acre/year) ____________________________________________________________________ Vegetated Swale 23.5 (9.5) Retention Pond 69.2 (28.0) Detention Pond 59.3 (24.0) Sand Filter 74.1 (30.0) Gravel Wetland 53.5 (21.7) Bioretention 51.1 (20.7) Porous Asphalt 14.8 (6.0)
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Also interesting to note is that although porous pavement is generally
perceived as prohibitive because of high maintenance costs, the porous pavement system in this study was actually found to have the lowest maintenance burden overall. Pavement vacuuming, which makes up the bulk of the costs associated with porous pavement maintenance, is a service that is increasingly available in the private sector. This fact in combination with the small number of maintenance tasks, all ranging toward predictive and proactive activities (inspection and proactive sweeping), keeps overall maintenance burdens low.
Marginal Costs. Marginal costs for maintenance activities associated with total suspended solids (TSS), total phosphorus and total nitrogen (TN) removal were converted to an annual cost per system, per watershed area treated, per mass of pollutant removed – $/ha/kg/yr ($/acre/lb/yr). Because TN removal efficiencies were not available for every BMP tested, dissolved inorganic nitrogen (NO3, NO2, NH4) was instead used. Capital costs for BMPs are presented in terms of per hectare of IC treated (2004 dollars), and maintenance expenditures are presented as an annualized percentage of capital costs, a measure routinely used for projected BMP cost estimates.
Figure 1 illustrates costs associated with maintenance over the years of study
per hectare of IC treated. Some systems such as the retention pond and the gravel wetland displayed cycling maintenance costs over the course of the study, while others, such as the bioretention and porous pavement systems, reached equilibrium after the first few years of operation.
Annualized data are summarized in Table 3 and Figure 2. In the majority of
cases, costs and personnel hours for LID systems were lower in terms of per mass of pollutant removed as compared to conventional systems. While the vegetated swale is the least costly system in terms of maintenance, it is also the least effective in terms of annual pollutant load reductions. This data indicates that marginal costs and marginal pollutant load reductions for LID systems are easier and less costly to maintain but still achieve greater pollutant load reductions. Exceptions occur with respect to any LID conventional BMP that does not have unit operations and processes that effectively target nutrients. Sand filter maintenance burdens can be regulated by reducing hydraulic loading ratios (watershed area: treatment area). However, in cases where costs per mass of pollutant trend toward unrealistic levels, alternative systems or treatment train approaches should be adopted as primary water quality management measures.
Maintenance as a Percent of Capital Cost. Maintenance costs are a substantial portion of the life-cycle costs of stormwater management practices. Estimates can vary and there may be economies of scale for larger systems. As illustrated in Table 3, annual maintenance expenses as a percentage of capital costs ranged from 5% to 23%. Maintenance costs for the retention pond equaled total capital construction costs after only 4.5 years of operation. LID systems, with the
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exception of the sand filter, had higher capital costs but lower annual maintenance costs as compared to the conventional retention pond and detention pond systems. As shown in Table 3, the lowest LID treatment system annualized maintenance costs expressed as a percentage of capital costs were porous asphalt (5%) followed by bioretention (9%) and the subsurface gravel wetland (10%). At these costs, annual LID system maintenance expenditures will equal total upfront capital costs after 11 years for bioretention and the subsurface gravel wetland system, and after 20 years for the porous asphalt system.
Conclusions
Many communities are struggling to define stormwater BMP maintenance
needs in the absence of clear documentation. As a step towards providing this information, maintenance activities and costs for a range of stormwater management strategies were calculated. Marginal costs, maintenance frequency, level of effort required, complexity, and pollutant load reductions were all factors that were considered. Annualized maintenance costs were lower for vegetated filter systems (bioretention and gravel wetland) and porous pavement and higher for retention and detention ponds. Stormwater treatment systems are increasingly selected for their water quality treatment potential, when TSS load reductions were considered, marginal maintenance costs were higher for conventional systems and lower for LID systems with vegetated swales and sand filters as the exceptions. When nutrients such as nitrogen and phosphorus were considered, marginal maintenance costs were higher for conventional systems and lower for LID systems with vegetated swales and sand filters as the exceptions. When nutrients such as nitrogen and phosphorus were considered, marginal maintenance costs per mass removed ranged from reasonable to cost prohibitive especially for systems with no nutrient removal mechanisms.
Examination of annual maintenance expenses as a function of capital
construction costs indicate that LID systems have higher upfront capital costs but lower annual maintenance costs as compared to conventional strategies, with the exception of vegetated swales and sand filters.
The results of this study indicate that generally, LID systems, as compared to
conventional systems, have lower marginal maintenance burdens (as measured by cost and personnel hours) and higher water quality treatment capabilities as a function of pollutant removal performance. Although LID system maintenance will be different and may require additional training, it should not require unusual burdens for management.
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Table 3: Summary of maintenance costs, capital costs and cost comparison per kg removed of TSS, TP and TN as DIN
Total Suspended Solids -- Annual Load of 689kg per Hectare IC Treatment System RE Annual Annual Ave Maintenance Capital O&M Kgs Maintenance Cost/kg/ha/yr Cost as a
Removed per Hectare %CC ______________________________________________________________________________ Vegetated Swale 58% 399 $2,000 $5 $28,000 7% Retention Pond 68% 468 $7,600 $16 $34,000 22% Detention Pond 79% 544 $5,900 $11 $34,000 17% Sand Filter 51% 351 $7,000 $20 $31,000 23% Gravel Wetland 99% 682 $5,300 $8 $55,000 10% Bioretention 87% 599 $4,700 $8 $49,000 9% Porous Asphalt 99% 682 $2,700 $4 $54,000 5%
Total Phosphorus -- Annual Load of 2.95kg per Hectare IC
Treatment System RE Annual Annual Ave Maintenance Capital O&M Kgs Maintenance Cost/kg/ha/yr Cost as a
Removed per Hectare %CC ______________________________________________________________________________ Vegetated Swale 0% 0.003 $2,000 $690,000 $28,000 7% Retention Pond 0% 0.003 $7,600 $2,600,000 $34,000 22% Detention Pond 0% 0.003 $5,900 $2,000,000 $34,000 17% Sand Filter 33% 0.97 $7,000 $7,100 $31,000 23% Gravel Wetland 56% 1.65 $5,300 $3,200 $55,000 10% Bioretention 34% 1.00 $4,700 $4,700 $49,000 9% Porous Asphalt 60% 1.77 $2,700 $1,500 $54,000 5%
Dissolved Inorganic Nitrogen as Total Nitrogen -- Annual Load of 26.6kg per Hectare IC Treatment System RE Annual Annual Ave Maintenance Capital O&M Kgs Maintenance Cost/kg/ha/yr Cost as a
Removed per Hectare %CC _____________________________________________________________________________Vegetated Swale 0% 0.027 $2,000 $77,000 $28,000 7% Retention Pond 33% 8.76 $7,600 $860 $34,000 22% Detention Pond 25% 6.64 $5,900 $890 $34,000 17% Sand Filter 0% 0.027 $7,000 $260,000 $31,000 23% Gravel Wetland 98% 26 $5,300 $200 $55,000 10% Bioretention 22% 5.86 $4,700 $800 $49,000 9% Porous Asphalt 0% 0.027 $2,700 $100,000 $54,000 5%
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Future Research Future research needs include a comparison of this data with maintenance of other common items such as standard parking lots, crack sealing and catch basin infrastructure as a comparison to porous asphalt parking lots. Standard landscaping activities should also be compared with maintenance tasks associated with routine maintenance of bioretention facilities. Acknowledgements
The UNHSC is housed within the Environmental Research Group at the University of New Hampshire (UNH) in Durham, New Hampshire. Funding for the program was and continues to be provided by the Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET) and the National Oceanic and Atmospheric Administration (NOAA). Additional thanks go out to Jeff Gunderson for his contributions and editing. References
Brown, S. A., Stein, S. M., and Warner, J. C. (1996). “Urban drainage design manual
hydraulic engineering circular 22.” FHWA-SA-96-078, Federal Highway Administration (FHWA), Office of Technology Applications, Washington, D.C.
Debo, T. N., Reese, A.J. (2002). Municipal Stormwater Management, Lewis Publishers LLC, Boca Raton, Florida.
Erickson, A.J., J.S. Gulliver, J. Kang, P.T. Weiss and C.B. Wilson (2010). “Maintenance for Stormwater Treatment Practices.” Journal of Contemporary Water Research & Education. Issue 146, pp. 75-82.
Federal Highway Administration (FHWA). (2002). “Chap. 3: Stormwater best management practices in an ultraurban setting: Selection and monitoring”. Dept. of Transportation Publishing Warehouse, FHWA, Landover, MD.
MacMullan, E. “Economics of LID.” EcoNorthwest, Eugene, OR, 2007. Narayanan, A. and Pitt, R. (2006). “Costs of Urban Stormwater Control Practices.”
Department of Civil, Construction, and Environmental Engineering, University of Alabama.
New Hampshire Dept. of Environmental Services (NHDES). (1996). “Best management practices for urban stormwater runoff.” NHDES, Concord, N.H.
New York Dept. of Environmental Conservation (NYDEC). (2003). New York State stormwater management design manual, Center for Watershed Protection, Ellicott City, MD.
Powell, L.M., Rohr, E.S., Canes, M.E., Cornet, J.L., Dzuray, E.J., and McDougle, L.M. (2005). “Low-Impact Development Strategies and Tools for Local Governments.” LMI Governmental Consulting.
Prince George’s County, Maryland Department of Environmental Resources (MDER) (2007). “Bioretention Manual”. Accessed online January 2012: http://www.princegeorgescountymd.gov/Government/AgencyIndex/DER/ESG/Bioretention/pdf/Bioretention%20Manual_2009%20Version.pdf
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Roseen, R. M., Ballestero, T. P., Houle, J. J., Avellaneda, P., Briggs, J. F., Fowler, G., and Wildey, R. (2009). “Seasonal Performance Variations for Stormwater Management Systems in Cold Climate Conditions.” Journal of Environmental Engineering-ASCE, 135(3), 128-137.
United States Environmental Protection Agency (USEPA). (2000). “Low Impact Development, a Literature Review”. United States. Office of Water (4203). EPA-841-B-00-005. Environmental Protection Agency Washington, D.C.
United States Environmental Protection Agency (USEPA). (1999). “Preliminary data summary of urban stormwater best management practices.” EPA-821-R-99-012, Washington, D.C.
Washington State University Pierce County Extension (WSU). (2007). “Maintenance of Low Impact Development Facilities”. Developed by Curtis Hinman, WSU Extension – Pierce County.
Weiss, P.T., Gulliver J. S., and Erickson A. J. (2005). “The Cost and Effectiveness of Stormwater Management Practices.” Minnesota Department of Transportation Report.
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Integrated LID and Green Infrastructure Planning at Rutgers University to Achieve Better Ecological Outcomes at Lower Cost
Ted Brown, P.E., M. ASCE1, Jennifer Dowdell1, Seth Richter2, Larry Porter2
1 Biohabitats, Inc, 2081 Clipper Park Road, Baltimore, MD 21211 USA, Phone: 410-554-0156 2 Rutgers University Abstract
Rutgers University recently completed a Stormwater and Landscape Management Master Plan for their Busch and Livingston Campuses. This plan provides an ecological and hydrological foundation for the University's future planning and development efforts through a low impact development (LID) and green infrastructure approach to stormwater and landscape management. The approach considers stormwater management as part of the broader ecological system using a combination of bioengineering techniques and native landscape practices within the campus context. Creating more sustainable green infrastructure requires transitioning from practices that may contribute to the degradation of the environment toward creating working landscapes that perform important ecological functions. Examples of these functions include: receiving, retaining, and filtering stormwater in a way that may preserve or mimic natural hydrological patterns (treating water as a resource, not as a problem); creating natural habitat for diverse ecosystems; providing educational opportunities; contributing to overall campus sustainability initiatives; and reducing the overall operation and maintenance burden for campus staff. This plan provides a unique approach to integrating low impact development practices with landscape ecological improvements, thinking holistically about broader ecological connections and implications while treating the more specific primary needs of the campus as a social and educational setting. After assessing the campus needs and coming up with an approach that strives to improve the health and function of the landscape, current and future stormwater conditions were modeled to better understand the implications of suggested practices and their ability to meet regulatory requirements for stormwater management. The plan also includes planning principles and design guidelines that emphasize a commitment to sustainable landscape and water management design. The master plan is intended to be flexible in terms of identifying techniques and practices that can be applied throughout various Rutgers University settings, while still being specific enough to reflect the unique ecological characteristics and opportunities on the Busch and Livingston Campuses.
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Introduction
The Stormwater and Landscape Management Master Plan for the Busch and Livingston Campuses of Rutgers University (Figure 1) grew out of planning efforts Rutgers has been undertaking since the completion of their Master Plan in 2003. The Stormwater and Landscape Management Master Plan employs a green infrastructure approach to defining an aesthetic that incorporates functional landscapes into the campus setting. The plan is presented as a series of map overlays accompanied by narrative that illustrate areas of preservation, regenerative development and design, stormwater detention/retention, and potential growth. It also highlights a system of green corridors and other natural features that create a comprehensive and fully integrated stormwater management system. In addition, design guidelines, a plant list, and site recommendations have been developed that integrate landscape architecture, site design and stormwater management, and systems maintenance as related to the potential future campus development and build-out through a phased approach. The final result is a prioritized implementation plan that endeavors to provide opportunities for integrated stormwater and landscape projects that meet multiple goals, are phased over time, and have planning level capital and maintenance costs.
Figure 1. Busch and Livingston Campuses at Rutgers, with Regional Context in inset A Green/Living Infrastructure Approach
The green infrastructure approach taken at Rutgers stresses the importance of a functioning natural system as an integral element in the developed landscape.
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Having green infrastructure as the foundation for development requires transitioning from more conventional landscape planning, engineering, and management practices that may contribute to the degradation of the natural environment, to practices that perform important ecological functions while providing users with functional spaces. In practice this means embracing the notion that ecological preservation and restoration practices can be an integral part of the built landscape and that the design of those practices is directly informed by the natural processes and functions occurring on a site.
Through the protection, enhancement, or creation of functional or “working” landscapes, Rutgers has the opportunity to demonstrate and embrace the manner in which water serves as a resource on the campus. These working landscapes also provide important habitat, micro-climate, and aesthetic benefits. In built environments (redevelopment and new development situations), the Master Plan emphasizes strategies that daylight water and incorporate it into active landscapes such as, courtyards, plazas, walkways, parking areas, buildings, etc. These strategies bring these spaces to life and actively and passively educate users of the spaces while treating surface runoff. In more natural or transitional areas across the campus, the emphasis of the Master Plan is on restoring, protecting or enhancing existing habitat while integrating it into the aesthetic of the campus.
Developing a strong and resilient green infrastructure network involves examining, interpreting and building upon the inherent patterns in the landscape, in an effort to build a site’s capacity for regeneration (Figure 2). This approach involves a strong focus on connectivity, and designing for stacked benefits at multiple scales with an appreciation for historic function but an understanding that in highly urbanized areas, where natural function may not return in its original form, that a new functional living system with natural characteristics can be introduced. Green infrastructure strategies called for in the Master Plan include the integration of many of the following practices: planting and design decisions including converting turf to natural vegetation; managing, preserving, and restoring healthy forest stands and ecological corridors along streams and waterways; maintenance decisions; the integration of stormwater management features as part of a “functional landscape”; integrating vegetation into building architecture in green roofs and living walls; integrating cisterns and other water capture and reuse systems; permeable pavement and other alternatives to impervious surface; natural outfall designs; onsite treatment of wastewater; the integration of renewable energy and transportation planning; carbon sequestration as a consideration in management of vegetation; and the inclusion of edible landscapes or urban agriculture as well a other programming decisions. Green infrastructure designs that incorporate these practices can scale up to the landscape ecological perspective and scale down to the site specific treatment of the landscape, delivering natural capital and goods and services for a more sustainable future.
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Methods
The Stormwater and Landscape Management Master Plan for Livingston and Busch Campuses is based on a combination of scientific analyses of existing and proposed conditions. These analyses encompass the review of existing data, mapping and plans; in-depth on site field investigations; and modeling of future hydrologic conditions under different design scenarios.
Figure 2. Existing and Potential Ecological and Hydrologic Connections and Patterns Desktop Analysis of Regional Setting and Characteristics
Utilizing GIS data, the design team developed a general understanding of overall land and hydrological patterns. This entailed examining and developing maps of the general land use/land cover, along with a detailed understanding of existing soil, climate, topography and geologic conditions. This starts to frame the existing conditions and drivers for stormwater runoff patterns and habitat potential. Further mapping was developed to show the watershed relationships that provide context for how the campus is related to the broader stream, river and wetland systems. Forest cover and other natural resource areas were examined as well to understand both local and regional connections to habitat.
Landscape Ecological Characterization and Assessment
An ecological field assessment of existing conditions on the two campuses was performed in order to characterize important ecological attributes and to provide
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recommendations for enhancement or restoration. This assessment informed the master planning process by evaluating attributes such as geology, soils, vegetative communities, surface hydrology (streams and wetlands), rare, threatened and endangered species, habitat integrity, landscape ecology and invasive species.
Landscape Ecology on Busch and Livingston Campuses
Forests are an integral component of the campus green infrastructure network, providing habitat, open space and recreational areas, connections to the regional ecosystem, teaching, research, and cultural opportunities, and stormwater management. A vigorous forest cover is also critical to maintaining water quality, healthy stream ecosystems and providing flood control (USEPA, 2012). In the case of the Rutgers Livingston and Busch Campuses there has been a long history of disturbance of the native vegetation and the hydrology including agriculture, residential development, the use of a major portion of the Livingston Campus as an army base during the World War II, and the eventual development of the University.
Field Investigation, Scoring and Analysis
Representative sites (i.e., contiguous patches of forest) on the two campuses were identified and then evaluated in the field using a site evaluation procedure which scores a site based on its habitat quality attributes and relevant landscape ecology principles. Attributes assessed included:
• diversity of vegetation, • percent canopy cover, • dominant tree age; • presence of invasive species; • habitat hub and linkage evaluation for integrity and size; • presence of rare and protected species habitat; • degree of incision and bank stability of streams; • buffer width and integrity along riparian corridors, • presence and quality of aquatic habitat, • wetland presence, quality and size
The scoring system and the resultant site scores were used in follow-up
analysis as a tool to help rank, or differentiate, the sites. An assessment score was calculated for each representative site and the campuses were divided into polygons (areas) based on forest community type and other information gathered. The campuses were broken down into three main levels of preservation value (Figure 3): high preservation value (red), medium preservation value (yellow), and low preservation value (green). The area of highest preservation value, Rutgers Ecological Preserve, is the zone identified where development should be avoided altogether. Smaller zones of medium preservation value have been identified where there is potential for improved ecological connectivity or habitat enhancement and where development should be limited. Finally natural areas on campus identified as low preservation value occurred mainly in areas where there has historically been a lot of
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disturbance leading to degraded habitat, including the spread of non-native and invasive plants and the dumping of soils and materials during construction. These areas should not be considered automatically available for development and instead require mindful planning and potential ecological enhancement as development goes forward. Stormwater Condition and Retrofit Opportunities
The campus stream resources and their watershed areas provide an underlying foundation for this plan. To the maximum extent possible, stormwater and landscape management decisions and design should reflect the watershed conditions and be carried out to protect and restore these resources over time. This includes consideration of riparian wetland zones, upland forest patches, and transitional zones between the built and natural environment.
Figure 3. Ecological Assessment Ranking
Research was conducted on historic hydrologic patterns on the campus through review of aerial photography. Historic photos from the 1930’s to the present were used to interpret and track the evolution of hydrologic patterns. The review revealed a dendritic network of streams that over time have been filled, piped, and/or diverted. The historic analysis informs the understanding of current conditions as well as the plan for regenerative and restorative practices in stormwater and landscape management on the Busch and Livingston campuses.
Currently across both campuses there are a limited number of stormwater management practices providing various degrees of water quality and water quantity control. Practice types include:
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• Underground detention vaults that provide only water quantity control; • Dry detention basins that provide quantity control and a limited amount of
water quality treatment; • Constructed wetlands that provide both water quantity and quality control.
The majority of these practices were designed and constructed prior to the existing State of New Jersey stormwater management regulations being fully in place (adopted in February 2004). Only a limited amount of new construction has occurred on campus since the new regulations have been in place.
The result of having limited stormwater management is the varying degree of impact to water resource and landscape elements across the campuses. Rapid stream corridor and upland assessments that were conducted across the campuses for the project effort documented streams with signs of channel instability, especially immediately downstream of storm drain outfalls. In addition, riparian floodplain zones show signs of impact as a result of the “flashiness” of the urban runoff being discharged through the storm drain system. Flashy systems are typical in developed settings where there is a lot of directly connected impervious cover. Flows are concentrated and delivered quickly to a point of discharge which leads to higher volumes, velocities and rates. This is in contrast to a more natural flow pattern where flows are slowed, filtered, and beneficially used by vegetation and soil. The challenge to the planner and designer is to develop and incorporate strategies and site features that mimic the hydrologic response of the undisturbed and natural landscape.
Existing Conditions Analysis Using 1D and 2D Modeling
Hydrologic modeling is a useful tool to apply when conducting stormwater master plans. Stormwater modeling for drainage areas within the Busch and Livingston campuses of Rutgers was performed using InfoWorks CS v 10.0, a commercial modeling software developed by Wallingford Software in the U.K. The modeling involved developing a baseline or existing conditions model and a future conditions model that reflects the future proposed development, often referred to as “buildout.” With these two model scenarios in place, it was possible to assess system response and relative effectiveness of a range of implementation strategies. This level of analysis was done at the watershed scale as well as the site or precinct scale.
Integrated one-dimensional (1-D) and two-dimensional (2-D) modeling was completed for existing conditions on the Livingston and Busch campuses to better understand the hydrologic and hydraulic behavior of stormwater conveyance, based on a combination of both known and assumed data. For the 1-D model, existing data sets were used to generate runoff scenarios, in order to characterize overland flow and the associated flooding potential on the two campuses. A 2-D add-on was used, which takes over when the manholes/stream sections experience flooding and the flow spills are then routed based on the topography of the floodplain or the drainage area.
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To understand the existing drainage patterns on campus and associated flow directions, initial subcatchments were delineated for the campuses based on surface topography and storm sewer infrastructure, including discharge points. A drainage point was assigned to storm sewer nodes placed at the most downstream end of each subcatchment, representing a storm drain outfall. Additional subcatchments were delineated based on field work that identified potential stormwater retrofit areas. The percent imperviousness of a subcatchment was calculated based on a GIS layer of imperviousness (buildings, parking lots, and roads). The surface roughness and infiltration characteristics were determined primarily based on soil data, but were supplemented by conditions observed during field reconnaissance (e.g., golf course and ecological areas have higher assumed infiltration characteristics).
The existing stormwater detention ponds on campus were also incorporated into the existing conditions model. Although the locations were known, the physical dimensions of such structures were not readily available. The dimensions were developed based on visual inspections and a review of Google Earth maps and were included in the 1-D and 2-D models as storage nodes with certain outlet characteristics (Figure 4).
Figure 4. Example of 2-D modeling output for Busch Stormwater Retrofitting as a Restoration Strategy
Stormwater retrofits refer to a variety of practices designed to help restore watersheds by providing stormwater treatment in locations where practices previously did not exist or were not effective. Retrofits are inserted into the landscape for four primary purposes: reducing pollutant loads, promoting shallow groundwater recharge, minimizing accelerated channel erosion, providing flood control and
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drainage problem relief. In addition, stormwater retrofits offer further benefits to the campus, including the following: • Beneficial use of rainwater – Collecting rainwater for landscape irrigation will
reduce potable water demand on campus.
• Education – BMPs such as rain gardens and turf conversion provide educational and stewardship opportunities to discuss the significance of upland hydrology as well as native vegetation.
• Sustainability – BMPs are an important component of a shift from active to passive landscape management. For example, after an initial establishment period, rain gardens require little maintenance except weeding, debris removal, and occasional plant replacement, as with any garden. Irrigation is not needed except in extended dry periods, and rain gardens thrive without fertilizer and chemical treatments.
• Habitat and Microclimates – Creating more diverse open space areas on campus that are also managing water provides valuable habitat for birds and insects. Areas planted with trees and shrubs also have the ability to provide shade to offset heat island effects and provide small microclimate pockets across campus which contributes to greater ecological diversity.
• Cultural - Providing physical and visual connections to natural processes, improved aesthetics, spaces for contemplation and rejuvenation, social gathering, quiet study, wildlife viewing, etc.
Stormwater retrofits generally fall into two categories that were defined for
this Master Plan: storage retrofits and on-site retrofits. Storage retrofits can provide a full range of controls (i.e., water quality and water quantity controls) and typically treat drainage areas greater than 5-10 acres. In comparison, on-site retrofits typically provide only water quality treatment and recharge benefits for smaller storms and treat less than five acres of contributing drainage area, and frequently less than one acre. Application of practices in the different categories vary according to the impervious cover and land use makeup of each catchment as well as the restoration goals being pursued. Storage retrofits, such as constructed wetlands, often provide the widest range of watershed restoration benefits; however, on-site retrofit practices, such as bioretention and filtering practices, can provide a substantial benefit when applied over large areas. For Rutgers, the goal was to identify a variety of retrofits opportunities across both major categories.
The pollutant removal efficiencies of various treatment practices can help determine pollutant load reduction potential and can be an important consideration in restoration efforts that are focused on a particular parameter of concern. More detailed information about treatment practice pollutant removal effectiveness can be found in the Center for Watershed Protection’s National Pollutant Removal
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Performance Database (2007a) and at http://www.cwp.org/documents/cat_view/76-stormwater-management-publications.html. Campus Retrofit Inventory
Retrofit inventory field work was conducted at the Busch and Livingston campuses in order to identify and assess opportunities in the campus landscape for stormwater retrofits. Candidate sites were initially identified using aerial photos and maps of impervious cover, soils information, topography, known storm drain infrastructure, and hydrology. Each candidate site was examined in the field for retrofit potential. This involved an assessment of the site’s drainage area, impervious cover, and land use; an evaluation of existing stormwater management and drainage patterns at the site; and identification of site constraints that may impede implementation, such as utilities and permitting factors. The goal was to identify a variety of retrofits opportunities and to become aware of the general character of the landscape and drainage patterns in order to better provide recommendations for stormwater management in the context of the physical master plan and planning for future development potential as well as for restoration of existing impacted natural resource and open space areas on campus. Good candidate retrofit sites on campus generally had one or more of the following characteristics: high ecological habitat value, located at a current nuisance flooding locations, large amount of impervious cover in the drainage area, insufficient existing drainage infrastructure or stormwater practices, and potential as a demonstration project.
Figure 5. Stormwater and Landscape Retrofit Locations at Busch and Livingston Campuses
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Over 50 stormwater retrofit opportunities were identified across the campus (Figure 5). The retrofit opportunities that have been identified for the two campuses can be categorized broadly as falling under of the following palette of practices: landscape conversion (e.g., turf to meadow, turf to forest), functional landscapes (e.g., bioretention, rain gardens, bioinfiltration), rooftop vegetation, permeable pavement, rainwater harvesting, underground filters, bioswale conveyances, outfall treatment, and stormwater ponds/constructed wetlands.
Landscape and Land Use Field Assessment
Land use and programming was evaluated on each campus as well as general circulation, gateway entry points, and vehicular and pedestrian conflicts. Pedestrian and bike behaviors were observed in order to understand unofficial routes chosen by the student body when traversing the campus. Campus open spaces lack strong defining landscape elements and large areas of surface parking disrupt the fabric of the landscape. Open spaces on both campuses are not used to their optimal potential.
In each of these cases, it was determined that improved signage and landscape treatment (including integrating low impact development stormwater practices) can provide existing entries an even stronger sense of arrival and way-finding. Where pedestrians experience areas of conflict with vehicular traffic on both campuses, opportunities were identified to integrate bike and pedestrian paths with potential stormwater management practices in a way that can provide buffers between the two. Similarly, a number of unofficial paths (desire paths) which experience heavy pedestrian use were identified for conversion to permanent trails or walks with enhanced landscape elements that also provide stormwater filtering functions. Larger open space areas were evaluated for potential as outdoor learning areas or landscape conversion zones (turf to meadow or forest).
Stakeholder concerns, observations and maintenance issues
A critical part of the planning process was including stakeholder input and participation. The Master Plan takes into consideration a variety of different perspectives, from the needs and challenges of facilities, utilities, and grounds maintenance staff; to the space and parking requirements for athletics and recreation activities. Of equal importance are the students and professors who use the campus space as both classroom and meeting space. Each of the key stakeholder groups offers a unique perspective of the campus landscape and institutional pressures and expectations, as well as knowledge of space needs for different user groups. Over the course of the project there were several opportunities for stakeholder participation and engagement. One example of the results from those sessions is shown below in Figure 6.
Working sessions with members of the campus community were a key component of the observations phase. Staff, faculty, and students –all of whom are daily users of the campus and are therefore much more aware of the nuances of its
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unique setting and history–were valuable assets during this phase, providing important details related to maintenance, current issues with flooding or nuisance stormwater, programming needs, and the successes/failures of current landscape maintenance and management standards. These individuals worked with the master plan team to formulate a set of planning principles as well as a list of specific design guidelines. The planning principles and design guidelines provide the basis for an approach to planning that advocates for the implementation of functional natural landscapes, or green infrastructure.
Figure 6. Stakeholder Input Graphic Identifying Campus Opportunities and Constraints
Results
The Master Plan incorporates functional landscapes into the campus context, focusing on the three components of stormwater, landscape ecology and circulation & connectivity. Together these provide a framework for future management and planning, while defining a renewed sense of natural function, social interaction, and spatial definition. Sustainable and regenerative stormwater management opportunities exist on both campuses, as well as opportunities for enhanced habitat areas.
The final master plan is presented as a series of map overlays accompanied by narrative that illustrates areas of preservation, regenerative development and design, stormwater detention/retention, and potential growth. It also highlights a system of green corridors and other natural features that create a comprehensive and fully
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integrated stormwater management system. In addition, recommendations have been developed that integrate landscape architecture, site design, stormwater management, and systems maintenance related to future development. All strategies were developed with the goal of meeting the range of stormwater and watershed management regulatory requirements Rutgers must meet as campus expansion occurs.
The plan articulates and incorporates: • Solutions to stormwater management that benefit the University through
ecologically based, aesthetically pleasing, multipurpose designs; highlighting opportunities that ‘engage, intrigue and educate’ the University community on stormwater management while enhancing water quality. Suggested low impact development-best management practices that satisfy and in some cases exceed requirements of the New Jersey Department of Environmental Protection’s Phase II stormwater rules.
• Policies and practices for the restoration, enhancement, and integration of the ecological and stormwater infrastructure systems; including:
• Preserving the natural and beneficial functions of the natural drainage system. • Restoration and management potential in natural areas on the periphery of the
campus, strengthening the ecological integrity and preserving interior forest areas. The provision for alternative native meadow zones and ecological connections which will have lower maintenance needs.
• Reducing runoff volumes and rates by minimizing impervious surfaces and disconnecting the flow of runoff over impervious surfaces.
• Establishing vegetated open-channel conveyance systems discharging into and through stable vegetated areas.
• Minimizing land disturbance (including clearing and grading) and minimizing soil compaction
• Protecting areas that provide water quality benefits or areas particularly susceptible to erosion and sediment loss
• Providing applicable concepts for low maintenance landscape practices that encourage planting of native vegetation and minimizing the use of lawns, fertilizers and pesticides.
• Management throughout the campus to eradicate nonnative invasive species and control future spread of these species
• Strong gateways that provide legibility to the campus but also invite the visitor and resident to experience renewed connections to the natural systems at select gateways
• Greater connections between the two campuses and the Ecological Preserve for pedestrian, bicyclists, and residents of the housing near the natural areas – providing natural amenities
• Research opportunities at all BMP retrofit sites and possibilities to integrate them into applicable curriculum across the academic departments
• A strengthening of the two campuses’ landscape ecology and aesthetic
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Landscape Ecology
The campus landscape ecology strategy promotes the unique integration of ecology and the human experience in a campus setting, weaving environmental health and preservation into a growing and expanding campus development plan through new and improved landscape practices. These practices include extensions of native habitat including grassland meadow, upland forest, floodplain forest, and wetland islands as well as the design of more human-centered landscapes with seating and gathering areas, native plantings and interwoven green infrastructure.
Stormwater
The stormwater portion of the master plan highlights the stormwater retrofit opportunities across the campuses. Stormwater retrofit opportunities for each campus were ranked and prioritized based on capital cost, water quality and quantity benefits, habitat benefits, time frame for implementation, and educational/demonstration value (visibility). The top two tiers of retrofit priorities were mapped as part of the stormwater layer to highlight sites for consideration. Besides the retrofit opportunities highlighted in the plans for Busch and Livingston, there are many opportunities for innovative stormwater treatment in areas targeted for future development. The standards to be met in implementing future stormwater management practices across both campuses are included in the Design Guidelines.
Design Precincts - The Busch Campus Dining and Residential Stormwater and Landscape Design
A more site-specific hydrologic, as well as spatial and visual, response to the inclusion of green infrastructure and alternative landscape treatments was developed to provide more detail about design implementation. One site was selected due to the challenging drainage and stormwater issues and new student housing. The focus of this precinct study is on the Busch Dining Hall parking lot and the connections across the street and into the residential quads. This is a key area to approach with the concept of integrated stormwater and landscape response since there is current evidence of damage to campus infrastructure which will require immediate consideration. It is also an important example on campus of the effectiveness of integrated planning and maintenance with overlapping maintenance responsibilities between facilities and housing. This area has a prominent student and faculty presence so there is ample opportunity to make this an educational and pivotal social space and enhanced ecological corridor in the campus landscape.
Campus-wide issues and opportunities that this site contains include: retrofit opportunities; parking lot drainage; bus stop interface with road and active pedestrian areas; residential land use with associated stormwater BMP issues; relationship to the natural edge (riparian); and social/residential space. The suggested stormwater concepts for this precinct suggest a combination of many LID practices to help improve the already impacted conditions in this area (Figure 7). It suggests practices
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begin in the parking lot and streetscape in the form of curb extensions and linear bioretention. As the water reaches the stormdrain infrastructure the concept suggests a partial daylighting of this stormwater stream as regenerative stormwater conveyance flowing through the center of the residential complex, in order to slow the water, allow for filtering and some infiltration, and provide an exciting landscape amenity that brings the stormwater to the surface of the student experience, and highlights ecological design on campus. The existing stormwater pond west of the residential area is expanded and extended to the south to allow for more retention. Stormwater wetlands are also suggested to the west of the residential parking lot as alternatives to the extension of the existing stormwater pond. And then finally another portion of the piped runoff is daylighting as a stream with enhanced riparian vegetation before it discharges into the existing stream system.
Figure 7. Stormwater Retrofit Opportunities Within The Busch Campus Dining Precinct Study
Implementation Plan – Phasing, Budget, and Maintenance
The final element of the Master Plan is an implementation plan that provides guidance for phased implementation over time that is responsive to a combination of regulatory, budgetary and educational needs. A three-tiered priority list of strategies (projects and programmatic elements) was developed that integrates stormwater retrofitting, ecological restoration, campus circulation and landscape architecture, and policy changes. The implementation of the priority strategies is presented using a phased timeframe (short, medium and long term), and includes planning level capital costs and potential maintenance costs. Costs were determined from various unit cost (e.g., cost per linear foot, cost per impervious acre treated, cost per unit area of practice, cost per volume treated, etc.) sources such as the Center for Watershed
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Protection’s Urban Stormwater Retrofit Practices Manual (2007b), project data from the project team, and professional experience and judgment. Table 1 provides the implementation plan detail developed for the project.
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Table 1. Final Implementation Plan for the Busch and Livingston Campus Stormwater and Landscape Management Master Plan
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Conclusion Applying a holistic, ecosystems-based approach, Rutgers developed a
Stormwater and Landscape Management Master Plan for the Busch and Livingston Campuses of Rutgers University. The plan foundation began by developing a sound understanding of the existing ecological conditions and green infrastructure resources of the 1,700 acres of campus and surrounding areas. Rutgers was then able to explore opportunities to enhance and integrate these assets throughout the campuses while also providing the highest level of water quality and quantity controls. The recommended strategies considered fiscal efficiency of treatment measures that optimize treatment capability, ecological function and landscape position. Long-term operation and maintenance considerations were also factored into the strategy to account for desired longevity and performance. The overall planning approach for this project focused on conservation, restoration and retrofitting and sustainable landscape and stormwater management for future development. Rutgers identified principles and techniques that could be applied throughout various University settings, yet were specific enough to reflect the unique ecological characteristics and opportunities on the Busch and Livingston campuses.
Acknowledgements
The authors would like to thank the many Rutgers staff, faculty and students that contributed to the planning effort as well as project partners Wells Appel (landscape architecture) and HDR/HydroQual (hydrologic modeling).
References Center for Watershed Protection. 2007a. National Pollutant Removal Performance
Database. http://www.cwp.org/documents/cat_view/76-stormwater-management-publications.html
Center for Watershed Protection. 2007b. Urban Stormwater Retrofit Practices Manual. i-Map NJ DEP Online Environmental Mapping Tool. NJDEP. http://www.state.nj.us/dep/gis/depsplash.htm.
New Jersey Department of Environmental Protection Stormwater and Nonpoint Source Pollution Website (http://www.state.nj.us/dep/stormwater/)
Rutgers Ecological Preserve (Kilmer Woods) informational website. NY NJ CT Botany Online hosted by Patrick Cooney. http://www.nynjctbotany.org/njnbtofc/kilmerwoods.html.
Rutgers University Vision for Livingston Campus website. Rutgers University. http://visionforlivingston.rutgers.edu/.
Rutgers University Facilities at the New Brunswick Piscataway Campus Website. http://facilities.rutgers.edu/
United States Environmental Protection Agency. 2012. Identifying and Protecting Healthy Watersheds.
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