introduction to stormwater management (post-construction) · 2011-02-21 · impaired lakes • 5045...
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Introduction to Stormwater Management
(Post-Construction)
Nikos Singelis U.S. EPA’s Stormwater Program
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Overview• Results of Survey of MS4 Operators• Water Quality Impacts from Post-
Construction Stormwater Runoff• Post-Construction Minimum
Measure
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CWP Post-Construction Assessment
• 94 responses from MS4 operators• Representation from 30 states• 86% from Phase II communities• Cities, counties, towns, regional
agencies• Almost 60% have had program <
10 years (stormwater is new function)
• About half have adopted post-construction ordinance
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What are the driving forces for stormwater management?
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regulatoryrequire-ments
impairedwaters
TMDLs outstand-ing
resourceprotection
waters
drinkingwater
protection
violationsof waterquality
standards
erosionproblems
flooding Other
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Are BSD/LID credits available to reduce reliance on structural controls
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Credits are notavailable
Conservation orrestoration ofnatural areas
Rooftopdisconnection
Non-rooftopdisconnection
Sheet flow tostream buffer
Grass channels
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Who is responsible for maintenance of post-construction stormwater facilities?
HOA responsibility4%
Private land owner13%
Hybrid 18%
Other5% Do not have a
regular inspection maintenance
program50%
Local government responsibility
10%
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What is your annual post-construction stormwater management program budget?
$10K-50K26%
$50K-100K11%
greater than $100K20%
no reported budget43%
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Identify main problems affecting your post-construction stormwater management program
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West Nile Virusand mosquitoes
Toxic/ hazardoussediments
BMPs becomingjurisdictional
wetlands
Liability fordrowning
Other
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Water Quality Impacts from Post-Construction
Stormwater Runoff
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Why is Stormwater a Problem?
Urban Runoff is the Source of Problems in:
• 34,871 miles or 13% of all Impaired Rivers and Streams
• 1,369,327 acres or 18% of all Impaired Lakes
• 5045 square miles or 32% of all Impaired Estuaries
* Note: The National Water Quality Inventory (305(b) Report) describes the quality of assessed waters. Many of the nation’s rivers, lakes and estuaries remain unassessed. The percentages above are based on assessed waters only.
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Effects of Development on Stormwater RunoffIncreases:• Impervious
surface area• Stormwater
volume• Stormwater
velocity• Deposition of
pollutants
Decreases:• Stormwater
quality• Ground water
recharge• Baseflow • Natural drainage
systems including riparian vegetative cover
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Consequences of Development to Urban Streams
• Increased rate and severity of flooding
• Increased erosion of stream banks and bottoms (stream widening and channelization)
• Increased sedimentation
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Consequences of Development to Urban Streams
• Increased chemical pollution• Altered biological populations• Degradation of riparian habitat• Increased stream temperatures
(loss of riparian cover)
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Common pollutants in urban stormwater
• Sediment• Nutrients• Oxygen-
demanding substances
• Pathogens• Trash
• Road Salts• Oil and Grease• Heavy Metals• Heat• PAHs
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Runoff Pollution
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CN=47
CN=58
CN=67
Blakeslee Creek
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CN=47
CN=67
CN=67
Blakeslee Creek
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70% increase in peak flow170% increase in runoff volumeFormer instantaneous peak flow now lasts ~4 hours
Blakeslee Creek
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In watersheds with less than 5% impervious cover, streams are typically stable and pristine, maintaining good pool and riffle structure, a large wetted perimeter during low flow, and a good riparian canopy coverage.
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At 10% impervious cover, the stream is more visibly impacted. The stream has approximately doubled its original size, tree roots are exposed, and the pool and riffle structure seen in sensitive streams is lost.
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Active erosion becomes much more evident at 20% impervious cover with decreased substrate quality due to more material “flushing” through the system.
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The surrounding area of this stream is also 20% impervious cover and shows stream erosion that is much worse than in the previous slide due to an absence of vegetation to hold together bank structure.
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Post-Construction Minimum Measure
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What are the benefits of a stormwater program?
• Meet regulatory requirements• Reduce flooding• Improve water quality• Prevent erosion• Preserve biological populations• Sustainable infrastructure
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What are the benefits of a stormwater program?
• Improve aesthetics• Protect riparian areas• Increase property values• Educate the community• Reduce infrastructure and
maintenance costs
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Phase II Minimum Control Measure:
Post-Construction Stormwater Management in New Development and
Redevelopment
• Develop a program, using an ordinance or other regulatory means, to address runoff from new development and redevelopment projects that disturb > 1 acre
• Implement strategies with a combination of structural and/or non-structural BMPs
• Ensure adequate long-term operation & maintenance (O&M) of BMPs
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Phase II Minimum Control Measure:
Post-construction Stormwater Management in New Development and
Redevelopment
• The BMPs chosen should:– be appropriate for the local community– minimize water quality impacts– attempt to maintain pre-development runoff conditions
• Participate in watershed planning efforts• Assess existing ordinances, policies, and programs
that address stormwater runoff quality• Provide opportunities for public participation
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Smart Growth and Low Impact Development
Integrating into the Stormwater Management
Framework
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Overview• Trends in Development
– Smart Growth
• Low Impact Development• EPA Expectations for MS4 Post-
Construction Programs
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Trends in New DevelopmentSmart Growth
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Trends in Development• Are we focused at the right level?
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Trends in Development• Need to consider what is happening
at a broader scale – neighborhoods, cities, watersheds
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Trends in Development
Current development trends are characterized by low-density housing, farmland conversion, and dependence on cars, which:•Consumes land at a faster rate•Transforms farmland•Separates houses from stores, businesses, and other land uses•Increases time spent in cars
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It’s how and where we are growing that are driving our significantly increasing rate of land consumption, not domestic population growth.
Land Development and Population Growth in the US, 1982-2002
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Development patterns• 80% of
residential development occurs on urban fringe or beyond
• 94% of that development on 1 acre or more
USDA Economic Research Service
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OR
Low Density Higher Density
Which is Better for Water Quality on a Watershed Basis?
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Program Planning at Various Scales
Need to expand the scale of current stormwater planning
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EPA Research on Smart Growth & Water
Scenario A: 1 unit/acre
Scenario B:4 units/acre
Scenario C:8 units/acre
Impervious cover = 20%Runoff/acre = 18,700 ft3/yrRunoff/unit = 18,700 ft3/yr
Impervious cover = 38%Runoff/acre = 24,800 ft3/yrRunoff/unit = 6,200 ft3/yr
Impervious cover = 65%Runoff/acre = 39,600 ft3/yrRunoff/unit = 4,950 ft3/yr
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Scenario B: 4 units/acre
Impervious cover = 20%Total runoff = 149,600 ft3/yrRunoff/house = 18,700 ft3/yr
Impervious cover = 65%Total runoff = 39,600 ft3/yrRunoff/house = 4,950 ft3/yr
Scenario A: 1 unit/acre
Scenario C: 8 units/acre
Impervious cover = 38%Total runoff = 49,600 ft3/yrRunoff/house = 6,200 ft3/yr
Accommodating the same number of houses (8) at varying densities
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And at the watershed level…Accommodating 10,000 units on a 10,000 acre watershed at different densities
The lower density scenario
creates more runoff and
consumes 2/3 more land than the
higher density scenario.
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In 20 years, they have doubled their populations...
So by 2026, they might look like...
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Smart Growth Principles • Mix land uses
• Take advantage of compact building design
• Create a range of housing opportunities and choices
• Create walkable neighborhoods
• Foster distinctive, attractive communities with a strong sense of place
• Preserve open space, farmland, natural beauty, and critical environmental areas
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Smart Growth Principles (con’t)• Strengthen and direct
development towards existing communities
• Provide a variety of transportation choices
• Make development decisions predictable, fair, and cost-effective
• Encourage community and stakeholder collaboration in development decisions
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Water Quality & Smart Growth• Density and
imperviousness are not equivalent
• Lawns do not equal undisturbed land, such as forests or meadows
• Low-density developments have more impervious infrastructure
• Growth is coming to the region—limiting density on a site doesn’t eliminate that growth
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Which is Better for Water Quality on a Watershed Basis?
Housing like this….
…is, by design, served by retail and roads like this
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Smart Growth Resources• Using Smart Growth Techniques as
Stormwater Best Management Practices – December 2005
• Protecting Water Resources with Higher-Density Development –January 2006
• Parking Spaces/Community Places, Finding the Balance through Smart Growth Solutions – January 2006www.epa.gov/smartgrowth
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Low Impact Development
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Good site design is critical to successful stormwater management
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Site Design• Traditional stormwater management
that focuses on moving water off the landscape often exacerbates the stormwater problem
• Techniques that manage stormwater on-site and promote infiltration result in:– Pollution reduction– Volume reduction
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Basic Premise of Low Impact Development
• Design site to minimize pollutant loadings and runoff volumes and velocities
• Use distributed small scale treatment systems
• Maximize infiltration/ground water recharge
• Reduce infrastructure costs• Protect ecosystem functions and
values
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Minimize Development Impacts
• Reduce storm pipes, curbs and gutters
• Reduce building footprints• Preserve sensitive soils• Reduce road widths• Minimize grading• Limit lot disturbance • Reduce impervious surfaces
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Design standards should encourage alternatives to curb and gutter where practical
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Common LID Management Practices
Disconnectivity
Bioretention (Rain Gardens, Infiltration Trenches)
Permeable and Porous Pavements
Green Roofs
Soil Amendment
Open Swales
Rain Barrels
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Disconnectivity
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Open Swales
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Bioretention
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Parking LotInfiltration
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Rain Gardens
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Permeable and Porous Pavements
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Green Roofs
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Soil Amendment
Soils amended to a depth of 12 inches
Soil aeration
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Other Local Ordinances• Modifying other local ordinances is
the key to successful implementation of LID and Smart Growth
• Look at:– Fire codes– Street codes– Building codes– Parking requirements– Etc.
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Functional Landscape Design
Low ImpactConventional
Conventional
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Construction Cost Comparison
Conventional Low ImpactGrading/Roads $569,698 $426,575
Storm Drains $225,721 $132,558
SWM Pond/Fees $260,858 $ 10,530
Bioretention/Micro — $175,000
Total $1,086,277 $744,663Unit Cost $14,679 $9,193
Lot Yield 74 81
Prince George’s County, Maryland
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Post-ConstructionSmart GrowthLow Impact Development
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Post-Construction Guidance
• Developing a comprehensive guide for Phase II communities
• Will include detailed guidance on program setup, creating an ordinance, sizing criteria, smart growth, low impact development, etc.
• Working with the Center for Watershed Protection to develop
• Publication late 2006
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Post-Construction Guidance
Program Planning at Various Scales
Ordinance
Development Review Process
Inspection for Permanent Controls
Maintenance
Tracking, Monitoring &
Evaluation
Enforcement
Administration
Design Guidelines
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EPA Expectations for MS4 Post-Construction Programs
• Five years after MS4 permit issued:• Post-construction ordinance in place
– Incorporates Low Impact Development BMPs– Includes detailed description of maintenance
responsibilities
• Post-construction manual– Includes design standards for LID BMPs
• Maintenance program fully operational– Municipal maintenance responsibilities– Homeowners, commercial, institutional
responsibilities– Inspect all BMPs using appropriate schedule– Training program on maintenance
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EPA Expectations for MS4 Post-Construction Programs
Five years after MS4 permit issued:• Planning and zoning processes
incorporate Smart Growth concepts and acknowledge the importance of stormwater management
• Sustainable funding/budget mechanism in development (entire stormwater program)
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Resources• EPA’s Green Infrastructure page
www.epa.gov/npdes/greeninfrastructure• Education and Outreach Materials
www.epa.gov/npdes/stormwatermonth• Training resources
www.epa.gov/npdes/trainingwww.epa.gov/owow/watershed/wacademy/
• Menu of BMPs www.epa.gov/npdes/menuofbmps• Smart Growth www.epa.gov/smartgrowth• Low Impact Development www.epa.gov/owow/lid
andCenter for Watershed Protection www.cwp.orgCWP’s Stormwater Manager’s Resource Center www.stormwatercenter.net
• MS4 Case Studies—approximately 20 www.epa.gov/npdes/casestudies
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Contact InformationNikos SingelisEPA, Office of Wastewater Management1200 Pennsylvania Ave, NWWashington, DC [email protected]
Sign up for NPDES News – our email newsletter at www.epa.gov/npdes