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PREPARED BY

ANDROPOGON ASSOCIATES

10 SHURS LANE, PHILADELPHIA, PA 19127 T | 215 487 0700

CAHILL ASSOCIATES

104 SOUTH HIGH STREET, WESTCHESTER, PA 19382 T | 610 696 4150

THE ROSE GROUP

621-101 HUTTON STREET, RALEIGH, NC 27606 T | 919 829 0555

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS

1.0 EXECUTIVE SUMMARY

1.1 BACKGROUND AND PURPOSE1.2 ENVIRONMENTAL OBJECTIVES1.3 REGULATORY CONTEXT1.4 PROCESS1.5 PRINCIPAL FINDINGS1.6 KEY RECOMMENDATIONS1.7 PILOT PROJECTS Pilot projects recently constructed and in construction Pilot Projects in the Planning / Design Stage 1.8 SUMMARY

2.0 ENVIRONMENTAL SETTING

2.1 WATERSHED CONTEXT2.2 DRAINAGE BASINS OF THE UNC-CH CAMPUS

Meeting of the Waters Creek Morgan Creek Chapel Creek Bolin Creek

Battle CreekHydrologic soils

2.3 HYDROLOGIC DATA RELEVANT TO THE STUDY2.4 EXISTING LAND COVER 2.5 EROSION AND SEDIMENTATION CONTROL2.6 TREE PROTECTION REQUIREMENTS

3.0 WATER BALANCE MODEL ANALYSIS

3.1 METHODOLOGY Runoff Volumes and Pollutant Loads

3.2 POLLUTANT GENERATION AND TRANSPORT Particulates “First Flush” Pollutant Transport Soluble Pollutants Flow Monitoring3.3 BEST MANAGEMENT PRACTICES

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4.0 BEST MANAGEMENT PRACTICES

4.1 BACKGROUND AND PURPOSE4.2 RECOMMENDED BEST MANAGEMENT PRACTICES4.3 STRUCTURAL BMPs

Permeable Pavements with Storage/Infiltration Beds Storage/Infiltration Beds under Other Surfaces

Runoff Capture and Reuse SystemsVegetated Roof Systems and Roof GardensWater Quality InletsRain Gardens

4.3 NON STRUCTURAL BMPs Pavement Cleaning Illicit Discharge Elimination Public Education and Outreach Integrated Pest Management Programs and Salt and Fertilizer Reduction Non-structural BMPs to slow runoff rates, reduce volume and absorb pollutants4.4 COMPARISON OF BMP EFFICIENCIES4.5 WATER QUALITY BENEFITS Introduction

Suspended Solids (SS)Chemical Oxygen Demand (COD) Water Quality Benefits by BMP

5.0 STORMWATER MANAGEMENT RECOMMENDATIONS

5.1 INTRODUCTION5.2 BMP APPLICATIONS BY WATERSHED5.3 ADDITIONAL BMP RECOMMENDATIONS TO MITIGATE LOCAL FLOODING5.4 SPECIFIC RECOMMENDATIONS TO MITIGATE FLOODING Western Portion of ME-1

Eastern Portion of ME-1 Portion of ME-1 above the Stadium Southern Portion of ME-1 5.5 CASE STUDIES / PILOT PROJECTS DEMONSTRATING BMP APPLICATIONS

Permeable Pavement with storage/ infiltration beds at the Friday Center Park and Ride Lot and the Estes Drive Storage Parking Lot

Alexander Connor Courtyard with Infiltration trenches Carmichael Field Rams Head Center and Ehringhaus Field Coker Arboretum Channel Restoration/ Pond Ambulatory Care Center Storage and Reuse School of Public Health5.6 SUMMARY

REFERENCES

APPENDICES

Appendix A Volume and Water Quality Statistics

Appendix B Stormwater Infrastructure InventoryData Dictionary InformationData Collection ProcessStructure ConditionPipe ConditionMajor Pipe SummaryMinor Pipe SummaryPipe ConflictsTrouble Spot Survey and Campus Interview(s)

Appendix C Regulatory Compliance Work Sheet - Town of Chapel Hill

Appendix D Recommended Native Plant Species List

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ACKNOWLEDGEMENTS

We would like to thank the following participants and planning partners who provided valuable guidance and insight during the planning process.

Stormwater Advisory Committee

Bruce RunbergAssociate Vice Chancellor for Facilities Planning and Construction

Carolyn ElflandAssociate Vice Chancellor for Campus Services

Dean BrescianiAssociate Vice Chancellor for Student Services

Anna WuDirector of Facilities Planning

Diane GillisArchitect, Facilities Planning

Bob MarriottSchool of Medicine

Mary BeckUNC-CH Health/Care

Cindy TaylorUNC-CH Health/Care/Environment, Health and Safety

Dee Jay ZermanUNC-CH Health/Care

Ray DuBose, P.E.Director, Energy Services

Margaret D. Holton, P.E.Water, Wastewater and Stormwater Manager

Kirk PellandGrounds Director

Sharon MyersEnvironment, Health and Safety

Willie ScroggsAthletics

Fred MuellerChair, Department of Exercise & Sport Science

Ed WillisDirector of Construction Management

Dave GodschalkChair, Building & Grounds Committee

Paula DavisMapping Manager

Cindy SheaSustainability Coordinator

Phil BerkeDepartment of City and Regional Planning

Jim WardCurator, NCGB

Pete ReinhardtDirector, Environment, Health and Safety

Jim MergnerFacilities Services

Bill BurstonHousekeeping Director

Larry BandGeography

Mark TwillaUNC-CH Health/Care

Seth ReiceDepartment of Biology

Steve AllredAssociate Provost for Special Initiatives

Peter WhiteDirector, NC Botanical Garden

Jill ColemanLandscape Architect, Facilities Planning

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E X E C U T I V E S U M M A R Y

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Figure 1-1 CHARACTER OF THE UNC-CHAPEL HILL CAMPUS SETTING (July 2001)

1.0 EXECUTIVE SUMMARY

1.1 BACKGROUND AND PURPOSE At present the University is in the midst of the largest expansion program in its 210-year history, with virtually every major program undergoing some change that will result in additional building structures and related facilities. This development influences all related programs, including the management of stormwater. The University has committed its resources and authority to campus-wide, long-term stormwater management and to the adoption of a Stormwater Management Plan to guide the implementation of these ideas.

The Stormwater Management Plan is funded under the State of North Carolina, Higher Education Bond. Its purpose is to support the comprehensive planning effort of the Eight-Year Development Plan. This includes providing a blueprint for mitigating the impacts of growth—by defining an alternative “sustainable” approach to conventional stormwater management, by describing “Best management Practices” (BMPs) that will improve the impacts of storm water runoff generated by the construction of new facilities and by identifying pilot projects that demonstrate these attitudes and these techniques.

A corollary purpose is to address stormwater management on a campus-wide basis—by organizing stormwater management into a coherent, integrated system and by defining the stormwater component of future building projects as contributors to this system.

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Figure 1-2 VIEW OF MAIN CAMPUS LOOKING ACROSS POLK PLACE (July 2001)

To support this plan, a Stormwater Advisory Committee was formed, representing the University staff and students as well as public agencies concerned with environmental regulation. One of the purposes of the committee was to generate consensus on the goals for the Stormwater Management Plan and to provide guidance to translate these goals into doable, effective projects.

This report fundamentally recommends a change in thinking. With this change, it is hoped that the University will incorporate sustainable stormwater management into every improvement opportunity—whether these opportunities are as large as a green roof system on a new building or as small as infiltration trenches incorporated into sidewalk repair. The cumulative benefits of many small solutions, such as rain gardens and tree trenches should not be underestimated for their impacts on water quality and quantity.

1.2 ENVIRONMENTAL OBJECTIVES

As the University has worked to meet the program needs of the future, the impact of that growth on the local environment has been increasingly important in the planning process. The Environmental Master Plan was included as part of the Campus Master Plan and established the following goals for the University of North Carolina-Chapel Hill (UNC-Chapel Hill) campus. Realizing that each of these goals is intertwined with the University’s stormwater management program, the development of an integrated plan to guide stormwater management at UNC-Chapel Hill was the logical next step.

1. Balance growth with preservation of the natural drainage system.• Reinforce the inherent natural beauty of the UNC-Chapel Hill Campusby creating building patterns that preserve stream corridors and forested steep slopes. • Make every building project the opportunity to restore some part of

the “natural infrastructure.”• Protect water quality by reducing or eliminating NPS pollutants scoured from the land surface, including soil, and minimizing erosion and the consequent sedimentation of streams.

2. Manage storm water as an opportunity not a problem. • Maximize present and future on-site infiltration of storm water to recharge ground water and absorb potential floodwaters. • Provide for capture and re-use of rainwater.• Manage total storm water volume on site or, at least, within the sub-basin with

an ultimate standard of no increase in runoff following development.

3. Recognize that UNC-Chapel Hill is part of the Cape Fear Watershed.• Enhance and protect the water quality of the surface streams to meet National

Pollutant Discharge Elimination System (NPDES) water quality standards. • Protect Jordan Lake, a major downstream water supply and recreation area.

Figure 1-3 VIEW OF MAIN CAMPUS LOOKING SOUTH (July 2001)

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4. Reinforce the University’s position as a Role Model:• Create and enforce University policies that permanently protect environmentally

sensitive land, reinforce and strengthen open space policies and plan for habitat protection.

• Reassign key land parcels to named protected areas.• Apply appropriate management strategies to certain critical land areas, such as

Morgan Creek floodplain, to ensure that management measures preserve the ecological functions of stream corridors, swales and drainage corridors.

• Monitor and assess all short and long-term land and water resource management objectives

1.3 REGULATORY CONTEXT

There are two regulatory programs related to stormwater that affect every component of this plan. The first of these is the local Town of Chapel Hill Zoning Ordinance for new development which imposes certain stormwater requirements. The second regulatory driver is the National Pollutant Discharge Elimination System (NPDES) Phase II Stormwater Regulations and the University’s required permit. While the Town ordinance concerns new development, only the NPDES program concerns both new and existing development and long-term stormwater quality and quantity.

Most of the proposed new development will take place within the municipal boundaries of the Town of Chapel Hill and includes a special zoning category for land use guidance called 0I-4. Previous regulation set limits of growth within this zone based on the total square footage of building space owned by the University. With the program needs identified in the Master Plan and the growth anticipated in both the Eight-Year Development Plan and the longer-range plan, it was apparent that previous limits would be exceeded. Evolving out of the re-zoning process, the Town and the University together developed a set of criteria for stormwater management applicable to the 0I-4 zones but also intended to lay the groundwork for the larger community.

Figure 1-4 MEETING OF THE WATERS CREEK (July 2001)

Figure 1-5 WOODLANDS OF SOUTH CAMPUS (July 2001)

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These criteria focused on three conditions for the Eight-Year Development Plan.

• No increase in the volume of post-development runoff for the 2-year rainfall (3.60 inches, 24 hour storm duration).

• No increase in the peak rate of runoff for the local 2-year (3.60 inches),10-year (5.38 inches), 25-year (6.41 inches), and 50-year (7.21 inches) frequency, (24 hour storm duration).

• A significant reduction in the annual load of non-point source pollution (NPS) discharged from new development with an 85% reduction in suspended solids during a 1 inch storm. This requirement is also part of Phase II NPDES.

North Carolina regulations for stormwater management are focused primarily on water quality impacts. Two related programs are mandated under federal law; the Cape Fear Watershed Water Quality Program and NPDES Phase II Stormwater Management Regulations. These evolving regulations will require the University to mitigate water quality impacts from both old and new developments on streams such as Morgan, Meeting of the Waters and Bolin Creeks.

Under Phase II of the NPDES program the discharge of stormwater will require a permit issued to each separate stormwater sewer system in publicly owned incorporated areas, larger than 10,000 people. UNC-Chapel Hill is a separate permit entity. Based on the list of impaired streams prepared by the State under the federal Clean Water Act, Section 303d requirements, the water quality concerns center on the eutrophic state of Jordan Lake. Prior studies in the Cape Fear Watershed, of which UNC-Chapel Hill is a part, have identified impervious surfaces and urban land uses as the root cause of these problems (2000 Cape Fear River Basin Plan, North Carolina State, Department of Water Quality).

While it has not yet been determined what specific pollutants are considered key for the reduction of enrichment conditions in Jordan Lake, recent discussions by the NC State Water Board have centered on the role of nitrogen. At present, it is nitrogen that drives the current stormwater management program in the adjacent Neuse River Basin and is under discussion for Jordan Lake. However, numerous studies of freshwater eutrophication have indicated that phosphorus is generally the limiting factor and in the Morgan Creek Watershed, the Orange County Water and Sewer Authority (OWASA) has invested heavily in programs to reduce phosphorous in their waste water effluent. This report recommends an approach consistent with this initiative.

In addition to meeting the Town’s stormwater management performance standards,Under NPDES Phase II, the University must meet State requirements for stream buffers. (Stream) buffers are required in water supply watersheds throughout the state as part of the Water Supply Watershed Management Program. The program requires local governments to adopt land use controls that include buffer protection. Phase II NPDES regulations require a 30 foot buffer along intermittent and perennial streams. The stream buffer requirement for critical areas within water supply watershed protection areas is 100 feet for perennial streams.

In order to meet these new regulatory requirements every new project at UNC-Chapel Hill will be expected to mitigate stormwater impacts within their site, to address any pre-existing flooding conditions and to meet the design guidelines established for various storm events for water quality. As each new project proceeds, the design team will be expected to consider the project both on a stand-alone basis, as defined by the disturbance area, and also as a component of the larger solution for a given watershed.

1.4 PROCESS

The Stormwater Management Plan has been an iterative process, evolving as each site and land management concept is tested and evaluated. Development of the Stormwater Management Plan for the UNC-Chapel Hill campus has included:

• An Infrastructure Study mapped the major pipes (over 12 inches in diameter) throughout the entire campus. The study also investigated flooding and illicit discharges and evaluated existing stormwater infrastructure to determine its capacity to convey the design storm required for roads and buildings.

• Stormwater quality and quantity impacts on the existing UNC-Chapel Hill campus, were analyzed and quantified for each of the

watersheds of campus streams—Meeting of the Waters, Morgan Creek, Chapel Creek, Bolin Creek and Battle Creek.

• Stormwater quality and quantity impacts were then analyzed for the Eight-Year Development Program.

• To further understand and to correct the potential for flooding in the 10 year and

the 100 year storms, as well as to evaluate the effectiveness of various BMPs, a supplementary detailed analysis of the hydrologic and hydraulic issues looked exclusively at a portion of the central part of the campus, sub watershed ME-1 in the Meeting of the Waters watershed. This study included additional review of the local infrastructure problems and investigation of flooding and illicit discharges.

Figure 1-6 VIEW OF THE CAMPUS LOOKING NORTH OVER THE BAITY HILL AREA (July 2001)

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• Best Management Practices (BMPs) were developed to address volume and rate reduction and the improvement of water quality to meet state and local regulations. BMPs identified and analyzed for use on campus are both structural and non-structural. Criteria of success for proposed BMPS included, meeting Town criteria, anticipating State criteria and implementing as many BMPs as possible.

Structural BMPs are primarily built elements that capture, store, reuse and where possible infiltrate stormwater. Non-structural BMPs are primarily management programs that avoid or reduce pollution and include conversion of existing land cover to vegetation types that can slow water, treat it and provide limited infiltration, maintenance programs that prevent or remove pollutants and public education efforts and on-going repairs of illicit discharges.

• There was close coordination with Town officials on the Town of Chapel Hill Zoning Ordinance for New Development.

• Several demonstration projects were implemented and several more are in the planning and design stage and the plan also includes recommendations for future projects.

1.5 PRINCIPAL FINDINGS

Analysis of existing and future conditions on campus, as well as testing of the effectiveness of various stormwater recommendations revealed several important findings:

1. Because development occurs largely in areas that are already impervious despite the number of projects planned, there is little increase in the total amount of impervious surface under the Eight-Year Development Plan (approximately 6.5 acres).

2. The amount of forested area and woodland decreases by 27 acres, while the amount of lawn increases by 30 acres. This has important ramifications for the aesthetic and environmental quality of the campus. An increase in lawn can also translate into an increase in fertilizer application and pollutant load. The loss of forest has implications for managing stormwater because forest areas infiltrate and clean water, reducing volume of runoff and pollutants.

3. The plan shows a reduction in the acreage of parking lots, a significant source of pollutants and an increase in the amount of roof areas, which are relatively clean. Therefore, with build-out of the Eight-year Development Plan, the amount of pollutants in the stormwater runoff should actually decrease.

4. If the majority of the proposed BMPs are implemented, stormwater volume reduction by watershed will exceed regulatory requirements as shown in table 5-17. In the Meeting of the Waters (ME) watershed, the overall potential to reduce runoff volume can more than double the amount required for compliance with the Town of Chapel Hill ordinance.

1.6 KEY RECOMMENDATIONS

This report has developed a number of recommendations to reduce the rate and volume of runoff as well as to alleviate flooding on campus and improve water quality. In developing the recommendations presented in this report, two guiding principles were followed:

1. It is best to manage stormwater where the problem is generated. This approach prevents exacerbation of downstream problems.

2. A number of Stormwater management options–large and small–distributed throughout a drainage area are inherently better than a single large solution, which if it fails, will have far larger consequences.

The recommendations were divided into four generic categories:

1. Best Management Practices (BMPs) both structural and non-structural:

a. Structural BMPs proposed for UNC-Chapel Hill campus include: • Storage and/or Infiltration beds in open spaces such as athletic

playfields • Pervious Paving with Infiltration/Storage Beds • Vegetated Roof Systems and Roof Gardens • Rain Gardens • Continuous Tree Trenches for Street Trees • Runoff Capture & Reuse systems, such as cisterns

• Water Quality Inlets, both small and large

b. Non-structural BMPs proposed for UNC-Chapel Hill campus include: • Conversion of existing land cover types

• Reduction of lawn • Redefinition of horticultural planting areas

• Conversion of woodland without understory to layered forest • Conversion of poorly established grass areas to meadow

• New management practices such as street sweeping and integrated pest management programs • Public education and outreach programs already in-place in the UNC- Chapel Hill Department of Environment, heath and safety

2. New Policies, Practices and Procedures:

Recommended new policies, practices and procedures include: • Integration of stormwater management issues early in the development and

review process at the University.• Establishment of a mechanism for the continuous collection and updating of relevant data on flow and water quality. Provision of an environmental accounting or cost benefits analysis of individual stormwater management elements shared between departments. Cost benefits should be determined by per pound of pollution removed or cubic feet of runoff removed for each individual BMP.

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• Provision of resources and support to improve land and water resource management in areas that do not have capital projects (such as Land Use Conversion).

• Establishment of funding guidelines to regain the present stormwater management and represent campus wide interests for long-term maintenance of the infra-structure and the future stormwater management system.

• Creation and implementation of education programs for faculty and students to promote involvement in long term campus watershed management.

• Development of partnerships to foster watershed awareness and planning, interdepartmental and inter-jurisdictional cooperation as well as implementation of land and water management and protection. The Stormwater Utility Development and Implementation Study Committee have already outlined some general guidelines and recommendations for joint programs based on their assessment of the current programs and regulations.

• Enforcement and Monitoring of Site Protection Measures at construction sites on campus. These protections include erosion and sedimentation control, protection of natural vegetation and protection of natural drainage elements.

• Establishment and continuation of on-going review of the Stormwater Management Program.

• Establishment of administrative procedures to ensure accurate, on-going accounting of projects that are in-compliance, non-compliant or that exceed expectations for Stormwater quantity and quality control.

3. Recommendations for Flooding: The Infrastructure Study, a separate study by the Rose Group, undertaken as a part of this plan, identified a number of areas where flooding could be seen or was reported, focusing on roadway overtopping, building flooding, property damage and risks to human safety. This flooding varies from nuisance flooding adjacent to walkways or building entrances to property damage where pipes run under existing basements with laboratory or mechanical and electrical equipment. This study also surveyed the large pipes 12 inches in diameter or more, throughout the campus, providing a systematic base map for the University’s stormwater drainage, updating the overall system plans.

As a supplemental hydrologic modeling task, under the Stormwater Management Plan, an intensive study of Meeting of the Waters Creek watershed, sub-watershed ME-1 was made to define the existing and potential impact of flooding solutions.

4. Recommendations for Illicit Discharges:

In order to meet the requirements of the University’s Phase II NPDES Permit specific tasks have been identified in order to assist in the detection and elimination of illicit discharges to stormwater. An important part of this program is the on-going mapping of the University’s stormwater piping system. The expected completion date for this mapping is 2006.

The University is developing stormwater educational programs and materials for Students, faculty and staff, to increase their awareness of how campus activities can impact water quality.

The University has initiated a dry-weather sampling program for streams on the campus. This program includes analytical field-testing or submittal of water samples for laboratory analysis. These results have helped the University to locate areas that may be impacted by illicit discharges. The University also inspects outfalls for signs of flow in dry weather and inspects University facilities and floor drains. A wet weather sampling program is also needed as this represents 95% of the NPS load.

Stream odors and unusual colors are reported to a University “hotline” by the public. Dye testing and other line inspections are used to specify the source of the discharges. Once these sources are identified they are eliminated.

The University is also working in cooperation with the Orange County Water and Sewer Authority (OWASA) to identify and eliminate illicit discharges from sewers to reduce pollutant and nutrient loads on local streams, lakes and wetlands.

1.7 PILOT PROJECTS

One of the principal tasks of the Stormwater Management Plan was to identify pilot projects that would demonstrate sustainable stormwater management approaches and techniques on the UNC-Chapel Hill campus. As might be expected, new development projects offer the greatest opportunities to incorporate significant stormwater mitigation measures in the most cost-effective way.

Several projects have either been designed or are currently being constructed. Projects constructed or in construction include Carmichael Field, Rams Head, the Science Complex Phase I and two other projects located off the main campus, the Estes and Friday Center parking lots. These projects represent important BMP demonstration sites and offer opportunities for the University to begin to evaluate and measure the benefits of the techniques, refine initiatives and establish performance standards. Proposed projects include those presently in the planning or design stages and include the Science Complex Phase II, the Global Education Center and the Bell Tower complex.

PILOT PROJECTS RECENTLY CONSTRUCTED AND IN CONSTRUCTION

The UNC-Chapel Hill Intramural Field No. 3 Drainage, Water Storage, and Irrigation Project (Carmichael Field) was the first project built under the new program initiatives and has been able to successfully demonstrate solutions to both water quality improvement and mitigation of flooding. This BMP, providing 550,000 (73,000 cubic feet) gallons of water volume stored, was the first measure recognized by the Town of Chapel Hill under their new development requirements. Storing the water, which can be pumped out and re-used for irrigation, reduces upstream runoff volume. If this water volume can be reduced through partial infiltration then it can be considered removed from the runoff, where water moves into the subsoil through the bed bottom. This project also corrected inlet placement to protect the Indoor Track facility from flooding.

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Ram’s Head

The Ram’s Head project, currently under construction, provides significant new stormwater management measures in the Meeting of the Waters watershed. These measures include infiltration beds underneath Eringhaus Field and a vegetated roof system, which combines evapo-transpiration from the vegetation and storage in cisterns on the plaza.

Where the original streambed was buried, the functions of the floodplain have been lost. The gravel beds constructed there will help restore these functions and reduce flooding by holding stormwater and allowing it to infiltrate slowly into the soil. A new stream channel is re-created along the edge of Eringhaus Field using surface runoff and seeps from the adjacent hillsides. This new stream will provide a natural, open swale that slows water velocity and treats runoff.

Estes and Friday Center Parking Lots

Two other projects, not located on the main campus, are the Estes and Friday Center parking lots. These lots represent unique initiatives in which subsurface stormwater retention is combined with two types of permeable pavement to produce two of the largest permeable pavement parking lots in the State of North Carolina. Use of a permeable pavement system (permeable paving with recharge beds underneath) demonstrates its feasibility for further use in selected parts of the campus.

Science Complex Phase I

The Science Complex Phase I included stormwater management in the form of storage/ detention/ infiltration beds that provide a total of approximately 17,600 cubic feet of storage. During a ten-year storm event, the Science Complex stormwater beds reduce the peak flow rate from the entire upstream drainage area from 26.1 cubic feet per sec to 13.3 cubic feet per sec, a reduction of almost half.

PILOT PROJECTS IN THE PLANNING/ DESIGN STAGE

Meeting of the Waters Creek is the largest single sub-basin on campus and the primary source of existing stormwater discharge from the campus. The storm sewer system in this area was built in increments and evolved to serve various buildings over a period of time. Various pipes and drains have been connected during the process but not always in a progressively larger conveyance system. The present system floods during heavy rainfall resulting in overflows of surface inlets, roadway, pavement and basement flooding. Because this drainage area has experienced significant development in the past and will shortly be the site of several major new land development projects and because this area is the most intensively studied on campus with the most detailed stormwater management recommendations, a number of pilot projects are chosen from this area. Two of these pilot projects are summarized below.

Science Complex Phase II

Phase II of the Science Complex will provide additional opportunities for stormwater management and a minimum additional storage/detention capability of 20,000 cubic feet is recommended. This storage/detention can take several forms, including the use of a simple green roof (which will reduce volume through evapo-transpiration), vertical storage, cisterns, and underground pipes.

In reviewing the stormwater management possibilities of this project, a low point in front of Venable was noted, where the pipes are near to the surface and flooding occurs. It is recommended that the University evaluate the opportunity to redirect the storm sewer to avoid this low area and instead convey upstream flows in pipe along South Road. In addition the pipes should be relocated so that upstream drainage is not brought through this area. A similar approach was taken at Rams Head, where 21 acres of drainage were diverted around, instead of piped underneath the new building.

Bell Tower Complex

The development of the Bell Tower Complex raises two stormwater issues; the impact on regional water quantity and quality within the Meeting of the Waters watershed (441 acres), and the localized flooding impacts within and immediately downstream of Sub-basin ME-1, the 84.8-acres of drainage above the stadium.

In order to offset the University’s proposed 8-year building program, the agreement with the Town of Chapel Hill requires a reduction in volume of 138,160 cubic feet of stormwater for the Meeting of the Waters watershed (drainage area 441.3 acres). This number is derived from the original analysis made for the Stormwater Management Plan by TH Cahill Associates and is shown in Table 5-17 in the report. These estimates are based on the 2-year frequency, 24-hour storm, with 3.6 inches of rain. A number of potential BMPs to provide this volume reduction were suggested and analyzed. A potential total of some 372,000 cubic feet of mitigated volume was listed in Table 5-17. This volume was distributed among a number of BMPs. Some of these suggested BMPs have been implemented and over time some have been relocated or deleted.

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In the detailed modeling study of localized flooding within ME-1, the potential role of the new Bell Tower Building was again considered. In the model, where the present impervious surface parking lot was replaced by the proposed new building footprint of 118,000 SF, there was little net increase in impervious surface. There was also the potential for substantially less pollution production, since the rainfall would now fall on the rooftop rather than on pavement.

The detention storage volume required to reduce the flood peak during the 10-year frequency rainfall was estimated at 55,000 CF, enough to prevent surcharging of the storm sewers immediately downstream—above and beneath the stadium.

The Bell Tower Complex also offers the opportunity to reduce both total runoff volume and to temporarily detain a greater volume of runoff, through capture and reuse systems, and by a vegetated roof system, through evapo-transpiration and detention. The 100-year rainfall was also analyzed for the sub-basin with the Bell Tower detention included, and surcharging of the pipes and manholes did occur downstream. Since prevention of surcharging for the 100-year rainfall cannot be totally mitigated by this single project, no estimate was made of the increase in detention storage for the greater event with this project as the only answer. The Bell Tower complex is only a part of the proposed solution to flooding within the 84,8-acre drainage above the stadium.

The potential additional volume reduction and detention storage on the roof was also not included in this model analysis, although the combined benefit could be substantial.

Global Education Center

Located at the top of the ME Watershed, the Global Education Center site offers a unique opportunity for stormwater management. The building design incorporates two underground stormwater storage structures, one of which serves as a cistern to supply water for flushing toilets in the building. It also includes two types of vegetated roofs. These measures will cumulatively hold 20,000 CF of water, mitigating the existing flooding downstream during the 10-year storm.

1.8 SUMMARY

Stormwater management has historically been left out of campus development, throughout the United States. With new regulatory issues, existing problems of flooding, illicit discharges and an ambitious new development program a new era has been initiated at UNC-Chapel Hill. As part of this new era, putting in place and following through on sustainable stormwater management policies and practices should allow the University to continue to grow, providing much needed facilities, while creating a more beautiful, coherent and functional campus.

Figure 1-7 EIGHT-YEAR DEVELOPMENT PLAN SHOWING NEW BUILDINGS, TOPOGRAPHY AND IMPERVIOUS SURFACE (July 2003)

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E N V I R O N M E N TA L S E T T I N G

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2.0 ENVIRONMENTAL SETTING

The University is located in both Orange and Durham Counties, in the North Central Piedmont, which has been described as a “vast plain of rolling knolls and hillocks dissected gently by minor streams, more boldly by the creeks and rivers”. (Godfrey p.12) The University holdings include all of these landforms from the broad, flat plateaus where the University was first located, to the wide, low lying floodplains of Morgan Creek, in the southeastern portion of the Mason Farm Property.

The Historic core of the University developed on a wide plateau where few stream valleys dissect the broad flat upland. Much of this land was repeatedly cleared of the native woodlands as part of the area’s agricultural past. Several large remnant trees from the original forest can still be found on the significant open spaces of this area of the campus at Polk and McCorkle Places and in the Coker Arboretum.

These mature trees are especially important to the landscape quality of the historic campus providing a sense of age and continuity. This land was well suited for the pattern of large T-shaped or L-shaped buildings that defined these central quadrangles. The historic quadrangles are large, continuous, lawns shaded by large canopy trees, some heritage trees that are relics of the agricultural landscape. As the need for new facilities increased, the University has grown to the south. This intensive development has resulted in a landscape with a very high percentage of impervious surface.

The steep forest slopes are critical components of the landscape of the southern portion of the campus. Although the entire University site was initially cleared for pasture and cropland, the steep slopes were eventually abandoned and left to grow back into forest. Today, the wooded hillsides of the Coker Pinetum and Kenan Stadium are important green corridors that punctuate the campus and make UNC-Chapel Hill an attractive and memorable place.

Figure 2-1 UNC-CH EIGHT YEAR DEVELOPMENT PLAN SHOWN IN THE LARGER ENVIRONMENTAL SETTING OF THE UNIVERSITY (July 2003)

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Historic maps trace the natural drainage patterns that once existed on the Main Campus. (Figure 2-4) These buried streams continue to influence drainage patterns because groundwater follows established sub-surface pathways, regardless of where the piped stream has been re-directed. An extensive stream network once flowed through the South Campus. College Branch, a tributary of Meeting of the Waters Creek, originated slightly west of Venable Hall, and flows southeast under South Road, before linking up with its main stem. This tributary flows directly underneath Kenan Stadium. As the University has grown, other natural stream channels have been buried and put in pipes, filling in and paving over many of the small stream valleys.

Two large important stream valleys are still preserved at the University as open space— Battle Creek in Battle Creek Park at the northeastern end of the campus and Meeting of the Waters Creek as it flows through the Pinetum on the western border. A remnant of a small tributary of College Branch also remains, located just west of the Bell Tower and east of the Bell Tower Parking lot.

Today, the UNC-CH campus extends to 739.9 acres, with over 39% of the campus covered with impervious surfaces—rooftops, parking lots and roads. This development has increased the volume of stormwater runoff during a 2-year storm event where 3.6 inches of rain falls in 24 hours, by about 21 million gallons in Meeting of the Waters Creek. This runoff volume is conveyed downstream by a complex system of pipes that underlie the campus.

As the University has become increasingly urban, landforms have been altered and the percentage of the land surface covered by built structures has significantly increased. Each new building or addition results in some loss of vegetation and every new surface parking lot adds more impervious surface. The increase in impervious surfaces—buildings, roadways, parking lots and sidewalks—produces a direct increase in stormwater runoff volume. Stormwater runoff also collects and transports pollutants producing the single greatest water quality problem in the nation—non-point source pollution. The main objective of the Stormwater Management Plan is to prevent or mitigate these impacts.

Historic Streams

Figure 2-2 HISTORIC STREAMS (July 2003)

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2.1 WATERSHED CONTEXT

The University is generally located within the larger Cape Fear River Watershed. Specifically, the southern-most portion of the campus is located within Cape Fear sub-wateshed 6, as identified by the North Carolina State, Department of Water Quality. (NCS DWQ) This watershed includes Morgan Creek, Meeting of the Waters Creek, and Bolin Creek along with the large sections of the town of Chapel Hill. Sub-watershed 6 drains entirely to Jordan Lake, which drains to the Haw River, which in turn flows into the Cape Fear River. In comparison with other sub-watersheds in the Cape Fear River Watershed, sub-watershed 6 contains a high proportion of heavily developed areas.

Biological assessment data from Morgan Creek indicate a downstream decline in water quality (2000 Cape Fear River Basin North Carolina, State Division of Water Quality). Good or excellent water quality results are recorded at upstream sites while there are only fair to poor bio-classification ratings as the stream flows through the urban and suburban sections of Chapel Hill. Meeting of the Waters Creek is identified as “Not Supporting” (NS), because of an impaired biological community. In-stream habitat degradation along with urban NPS Pollution is the probable cause of this impairment. In addition, two segments of Morgan Creek are identified as “Partially Supporting” (PS) and “Not Supporting” (NS) because of an impaired biological community. Possible causes of impairment are identified as sedimentation and urban non-point source pollution.

Figure 2-3 WATERSHED CONTEXT MAP-- CAPE FEAR SUB WATERSHED 6. INSERT SHOWS ENTIRE CAFE FEAR WATERSHED (July 2003)

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2.2 DRAINAGE BASINS OF UNC-CH CAMPUS

The largest and most developed watershed on the UNC campus is Meeting of the Waters Creek. This watershed includes 450 acres of the campus, 49% of which is currently covered with impervious surface. This drainage also represents 73% of the total campus impervious cover, with major development areas including the hospital complex, medical school, football stadium and other major sports complexes, as well as a variety of academic and student residential buildings.

A much smaller portion of the campus in the southwest corner drains directly to Morgan Creek, and comprises of 55 acres. This portion of the campus contains a number of existing and proposed buildings serving both the Hospital and the Medical School, with several existing residential buildings in the eastern area. Several major new structures are under construction or planned within this sub-basin, including the Ambulatory Care Center (ACC).

Battle Creek drains much of the heart of the original campus, flowing to the east and joining Bolin Creek. The land owned by the University includes 140 acres, 35 of which are impervious. Most of this development is the campus proper, and the holdings further to the east are currently undeveloped, forming what is known as Battle Park.

Portions of the main campus drain north and west into Bolin Creek and include the easternmost area around the Arts buildings along Airport Road. While representing a fairly small portion of the Campus (31 acres), Bolin Creek drainage is comprised of 18 acres of impervious buildings and pavement, or 53% of the land.

A small portion of the Chapel Creek Watershed, 78 acres, is owned by the university, and is comprised largely of open land with some recreational use. The developed lands within this drainage area consist of small recreational tennis courts and related parking, surrounded by single family residential properties.

Much of the surface and sub-surface drainage from the UNC-CH campus finds its way into Morgan Creek via Meeting of the Waters Creek. For purposes of analysis and land management, the watersheds of these streams on campus have been delineated along topographic boundaries. For larger stream systems, sub-divisions of each watershed were defined and identified by the name of the stream system of which they are a part, so that separate management solutions could be developed for different sections of the campus.

Figure 2-4 MAJOR WATERSHEDS OF THE UNC-CH CAMPUS (July 2003)

BOLIN CREEK

MEETING OF THE WATERS CREEK

BATTLE CREEK

CHAPELCREEK

MORGAN CREEK

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The impact of urbanization at UNC-CH is best seen in Meeting of the Waters Creek. The graph above compares the hydrograph for the Meeting of the Waters watershed before development to the present campus. The pre-development condition assumes an initial cover of forest and a Hydrologic Soils Group classification of B. Even in a 2-year storm of 3.6 inches there is little run–off. Under current campus conditions, with 48% impervious cover, and an assumed half of the remaining soil disturbed and now classified as hydrologic Group C, a 2-year storm of 3.6 inches will produce 2.8 million cubic feet of run-off—or 64 acre-feet—a six-fold increase. For the 100-year storm of 8.0 inches in 24 hours, the net increase in volume is 3.5 million cubic feet. The continuously increasing runoff over the past 70 years has severely impacted the Meeting of the Waters Creek, and reconfigured the channel to a broader and shallower section.

The sub-watersheds of Meeting of the Waters Creek can be grouped into larger aggregations, to better illustrate how they drain the campus. For example, sub-watersheds ME-1 and ME-4) above and below Kenan Stadium divide the drainage at a key juncture where a number of existing storm drains come together and are combined into a larger pipe passing under the Stadium and down the stream valley.

Figure 2-5 HYDROGRAPH COMPARING HISTORICAL CONDITION WITH PRESENT URBANIZED ME SUB-BASIN

MEETING OF THE WATERS CREEK (ME)

Meeting of the Waters Creek is the largest single watershed on campus and the primary source of existing stormwater discharge. This drainage area is subdivided into eight smaller watersheds (Sub-watersheds ME-1 through ME-8) in order to provide a better understanding of stormwater conditions on campus. This watershed drains 441.7 acres of the campus, with a high degree, 48%, of impervious surface. It represents 73% of the total campus impervious cover, illustrating the critical role of this drainage area in the development of a successful stormwater management program.

Figure 2-6 DETAIL OF EIGHT YEAR DEVELOPMENT PLAN SHOWING MEETING OF THE WATERS WATERSHED (July 2003)

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Figure 2-8 SUBBASINS ME-1 + ME-4 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)

Figure 2-7 illustrates the existing conditions of both sub-watershed ME-1 and ME-4. Sub-watershed ME-1 is a more developed drainage area of 84.8 acres with 65% impervious cover.

Figure 2-7 SUBBASINS ME-1 + ME-4 EXISTING CONDITIONS (July 2003)

Figure 2-8 adds the proposed new facilities of the Eight-Year Development program. Construction of Ram’s Head and the restoration of Ehringhaus Field are major projects in this area. In both sub-watersheds (ME-1 and ME-4), most of the new impervious surface will replace existing impervious cover. Proposed projects will not generate a significantly greater volume of runoff. However, by replacing dirty pavement with relatively clean rooftops the pollutant load will be lowered (except if the roofs are used for parking).

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Figure 2-10 SUBBASIN ME-2 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)

Figure 2-9 SUBBASIN ME-2 EXISTING CONDITIONS (July 2003)

Sub-watershed ME-2 is the most highly urbanized area of the entire campus, with a current impervious cover of over 78.4% and very little remaining green area. Two large parking garage structures (which combine to represent over 6.7 acres) are a significant portion of the total impervious cover in this drainage area. Patches of lawn surround existing structures. There are extensive underground utility lines just below much of this open land, especially in corridors along the roadways, making it difficult to use these areas for storage or infiltration.

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Sub-watershed ME-3 is a less developed portion of the campus. While there are a number of buildings on the western side, the lower and middle portions are athletic facilities and playing fields. The major open space within this drainage area is the historic town cemetery, the largest single parcel of open land not owned by UNC-CH within the campus boundaries. The amount of impervious surface in ME-3 is substantially less than the more central sub-watersheds.

Figure 2-12 SUBBASIN ME-3 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)Figure 2-11 SUBBASIN ME-3 EXISTING CONDITIONS (July 2003)

The most significant alteration of the original hydrologic pattern in sub-watershed ME-3 is the filling of the natural floodplain along the small stream valley to provide flat surfaces for athletic fields. Recent excavation for the Carmichael Field infiltration bed in the upper portion of this drainage exposed the original stream valley, which had remnant tree, stumps over ten feet below the present land surface.

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ME-5 is substantially larger than the other sub-basins within the Meeting of the Waters Creek watershed. Current land use is largely residential facilities and recreational buildings such as the Dean E. Smith Student Activity Center and the Koury Natatorium.

Figure 2-14 SUBBASIN ME-5 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)Figure 2-13 SUBBASIN ME-5 EXISTING CONDITIONS (July 2003)

In sub-watershed ME-5, the existing student family housing is being replaced by new housing on Baity Hill. The current impervious cover of 48.56 acres will increase by 2.6 acres with the development proposed in the Eight-Year Development Plan.

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ME-6 is a small sub-watershed defined by the long creek valley that runs north to south. The forested hillsides are known as the Coker Pinetum, which provides a natural forested boundary in the eastern part of the campus. A trail through the Coker Pinetum connects the N.C. Botanical Gardens to the main campus.

Sub-watersheds ME-7 and ME-8 are at the bottom of the Meeting of the Waters drainage area. They have only a small percentage of impervious cover. The Baity Hill Student Family Housing project extends into both of these sub-basins as well as ME-5. These sub-watersheds are primarily steep forested slopes and form the southern boundary of the campus.

Figure 2-15 SUBBASINS ME-6, ME-7, ME-8, AND ME-9 EXISTING CONDITIONS (July 2003) Figure 2-16 SUBBASINS ME-6, ME-7, ME-8, AND ME-9 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)

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MORGAN CREEK (MO)

The Morgan Creek watershed (MO-1) drains 55.3 acres from the southwest corner of the UNC-CH main campus and has a high percentage (46%) of impervious cover. Most of the original woodland has been removed or disturbed, leaving forest only on the steeply sloping sides of the four small swales that form the headwaters of this drainage system. Like much of the campus, this drainage area occupies the edge of a plateau, but here the land drains downhill into one of the residential communities of Chapel Hill.

Figure 2-17 SUBBASIN MO-1 EXISTING CONDITIONS (July 2003) Figure 2-18 SUBBASIN MO-1 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)

Since the University occupies the high ground in this watershed, existing development has caused problems in the adjacent community, including erosion, deteriorating water quality, as well as diminished low flow in the stream, decreased groundwater recharge and increased flooding. Impacts to several residences immediately adjacent to the campus and to Jones Park, a small downstream natural area, are the most visible. MO-1 has a number of existing and proposed buildings serving both the Hospital and the Medical School and several existing residential buildings in the eastern portion. New structures are planned or under construction within this sub-watershed, including the Ambulatory Care Center (ACC).

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CHAPEL CREEK (CH)

The Chapel Creek watershed is largely open and used mainly for recreation. Related parking surrounds the fields and tennis courts and the entire property is bounded by single family residential properties.

Figure 2-20 SUBBASIN CH-1 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)Figure 2-19 SUBBASIN CH-1 EXISTING CONDITIONS (July 2003)

No land development is planned or anticipated in the Chapel Creek watershed, and the existing impervious surfaces of parking lots and tennis courts do not, at present, offer opportunities to implement mitigation measures. If future plans include land development, a low impact land plan should be developed to reduce the stormwater impacts.

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Figure 2-21 SUBBASINS BO-1 AND BO-2 EXISTING CONDITIONS (July 2003)

Figure 2-22 SUBBASINS BO-1 AND BO-2 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)BOLIN CREEK (BO)

At 27.4 acres, Bolin Creek is the smallest drainage area on the campus and drains to the north and the northwest with 13.7 acres of impervious surface. Located in the historic core at the northern end of the campus the land is relatively flat, well-drained and less disturbed. It has a very old stormwater infra-structure. Open land is organized into quadrangles with very old canopy trees with large root systems. Preservation of these historic trees is very important.

Little is scheduled to change in this area and stormwater management should focus on capture, storage and reuse for irrigation of the qudrangles, as well as infiltration in tree trenches. Mitigation measures such as these are included in the Arts Complex plan and should reduce both the volume and pollutant load flowing to the Town of Chapel Hill.

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Figure 2-24 SUBBASIN BA-1 EIGHT-YEAR DEVELOPMENT PLAN (July 2003)Figure 2-23 SUBBASIN BA-1 EXISTING CONDITIONS (July 2003)

This portion of the campus, sub-watershed BA-1 includes a number of historic areas and structures, including the Coker Arboretum and several residential buildings. This area of the campus is considered a very high quality environment and is greatly valued by the University community. The design of the Eight-Year Development Plan brings development patterns characteristic of the historic core to the re-design of the southern end of the main campus.

BATTLE CREEK (BA)

The portion of Battle Creek watershed on campus, drains much of the heart of the historic core of the campus, flowing to the northeast. Of its 136 acres; 33.3 are impervious. Holdings further to the east are currently undeveloped. This watershed contains the large open space known as Battle Creek Park, located in the forested valley of Battle Creek.

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Table 2-1

MAJOR WATERSHEDS AND IMPERVIOUS COVER OF THE UNC-CH CAMPUS

WATERSHED AREA IMPERVIOUS. IMPERVIOUS (Acres) (Acres) COVER (%)

MTG. OF THE WATERS 441.7 215.2 48.7%MORGAN CREEK 55.3 22.2 40%CHAPEL CREEK 79.5 7.4 9.3%BOLIN CREEK 27.4 13.8 50%BATTLE CREEK 136 33.3 24.5%

TOTALS 739.9 29.9 39.5%

HYDROLOGIC SOILS

The natural hydrologic response of the soil to rainfall is to allow an initial amount of precipitation to infiltrate into the surface at a rate that is controlled by the physical properties of the soil and the type of vegetation growing there. Soil is constantly being formed at the bedrock/surface interface with the uppermost layer of bedrock constantly eroding, so that the “newest” soil is on the bottom. The growth of plant roots and a complex food chain of micro and macro organisms enrich the soil surface with organic matter, while wind and water transport some soils to locations beyond the original sites.

The soils that underlie the UNC campus have weathered from rocks that date back over 600 million years. The weathering processes presently date to the most recent retreat of the glaciers—about 15,000 years ago. Although that ice sheet did not reach Chapel Hill, it dominated the local climate and weathering processes. Most of the soils in the region have a surface that is relatively well drained and has supported dense woodland for thousands of years, but in many areas a heavier clay layer exists at a shallow depth of a few feet. Where human activity has cleared the original woodland for cultivation or building, the surface layer has been removed, graded and frequently compacted, greatly reducing the natural ability of the soil to infiltrate rainfall.

Existing soils vary greatly with soil series that reflect a more permeable surface horizon and an underlying heavy clay layer. Given the high Evapo-transpiration rate and low base flow that characterizes the annual water balance of Orange County and Chapel Hill, the critical question for stormwater management is how to sustain the natural hydrologic balance after severe alterations of the system.

To analyze the impact of rainfall and the resultant runoff, soils are grouped by “series”, and these “series” further classified by Hydrologic Groups. these groups describe how these soils respond to rainfall and produce runoff. Originally these categories were made for agriculture, so that well drained soils that allowed rapid tilling following rainfall were classified as the best soils for farming— Hydrologic Group A, Hydrologic Group B was well drained and Hydrologic Group C less well drained, with possible high water table or shallow bedrock conditions and finally Hydrologic Group D was poorly drained and generally found in floodplains and wetlands.

Figure 2-25 HYDROLOGIC SOILS GROUP (July 2003)

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30” AND HIGHER ESTIMATEDEVAPOTRANSPIRATION8 -10” IMMEDIATE

STORMWATER RUNOFF

12 - 16” ANNUAL AVERAGE STREAM DISCHARGE (COMBINED RUNOFF +

BASE FALL)

PRECIPITATION 42 - 48” ANNUAL AVERAGE

GROUNDWATER BASEFLOW 4”- 6”

2.3 HYDROLOGIC DATA RELEVANT TO THE STUDY

Mean Annual Precipitation According to the National Oceanographic and Atmospheric Administration (NOAA) annual precipitation in the area ranges from 42 to 48 inches. For the purposes of this study mean annual precipitation is assumed to be 46 inches per year. The wettest year reported was 1989 with 54.21 inches and the driest year was 1976 at 33.71 inches. Severe back-to-back droughts occurred in 1976-77, and in 2000 through October 2002.

Annual Runoff and Base Flow

Base flow is “ the water that percolates downward until it reaches the groundwater reservoir and then flows to surface streams as groundwater discharge.” (Viessman, et al, 1996). Between precipitation events, ground water provides the base flow to the stream channel. When the land is paved over, infiltration is converted to runoff and recharge cannot occur. Since streams are the surface expression of the ground water table, in the periods between precipitation, flow in streams is significantly reduced, because the ground water table has not been recharged.

The combined figures for annual runoff and base flow are frequently given for the region as 15 inches, equivalent depth (Linsley and Franzini, 1979), with the long-term average discharge exceeded only 20 percent of the time.

Annual Evapo-transpiration (ET)

Mean annual evaporation in shallow lakes and reservoirs was reported by the National Resources Conservation Service (NRCS) to be about 41 inches. Typical values for evapo-transpiration were not found. The process of estimating this effect is complex and is affected by local conditions. There is considerable interest in researching the values for evapo-transpiration and the State Climate Office of North Carolina will begin to gather data in the near future.

Figure 2-28 WATER BUDGET FOR UNC-CH CAMPUS REGION (July 2003)

Figure 2-27 ERODED STREAM BANKS AND LOW BASE FLOW IN TRIBUTARY OF MORGAN CREEK BELOW SUB WATERSHED MO-1

Figure 2-26 BATTLE CREEK IN BATTLE CREEK PARK

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Figure 2-29 EXISTING LAND COVER (July 2003)

All of the original soils on the UNC-CH campus were classified as Group B, but disturbance has reduced infiltration capacity. For the purposes of the water balance model analysis in this study, initial calculations assumed the soils should be instead classified as Hydrologic Group C, in the disturbed landscapes of the campus where the engineering, geology and soil science community have experienced very slow permeability in soil tests. Where removal of the upper soil layer has taken place, and fill added and compacted, the resultant soil may be almost impervious. Groundwater recharge through infiltration will be difficult to achieve in these disturbed landscapes.

2.4 EXISTING LAND COVER

Land cover determines how much runoff is produced on the campus and the quantity and types of pollutants generated and transported by that runoff. As the land cover data was reviewed for this study, it was apparent that the campus had undergone significant changes between the original photo base of 1998 and the continuously changing present.

Field studies refined the information from aerial photographs, identifying additional impervious surface. Geographic Information Systems (GIS) was used as a primary analytical tool for the water balance model. In order to quantify the amounts of stormwater runoff currently generated and to estimate the increase in runoff after redevelopment of the campus, land cover types at UNC-CH were classified by their permeability.

Land Cover is generally considered as pervious or impervious. However, in order to model more accurately how a change in land cover will impact the runoff volume produced by a given rainfall, additional classifications were created to describe the land surface that has been disturbed and probably compacted such as campus lawns.

Impervious surfaces were sub-divided by their potential to generate pollution, with roofs distinguished from more polluted roadways and parking lots. Figure 2-29 shows all the impervious surfaces within the campus, representing almost half of the 739.9-acre campus.

The pervious surfaces, initially distinguished as forest, lawn and meadow, were further sub-divided into additional classifications. These additional cover types helped to identify the management of the landscape, including the use of fertilizers and irrigation. Figure 2-30 illustrates all of the pervious surfaces currently found on the UNC-CH campus, from undisturbed forest to well maintained turf. These land cover classifications are described in Table 2-3.

Existing Land Cover Types

Forested land cover is the most effective in handling stormwater run-off and pollutant reduction, a role that should be recognized and preserved. Areas in forest retain spongy, absorbent soils that hold water, allowing it to seep slowly back in to the groundwater. On the southern portion of Main Campus, the slopes that have been left in forest are the major areas of recharge, returning water to the aquifer.

Managed woodland is a cover type resulting from the removal of the understory and shrub layers as well as many of the canopy trees, leaving only a few widely spaced large trees on a previously forested site. The ground layer is frequently bare in this type of woodland. It is nearly impossible to establish turf grass in managed woodlands due to competing tree roots

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Figure 2-30 EXISTING PERVIOUS COVER (July 2003) Figure 2-31 EXISTING IMPERVIOUS COVER (July 2003)

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and the fact that Conifers and Oaks leave a highly acid residue that prevents the growth of turf grass. There is some leaf litter, a few vines and occasional herbaceous plants, making the ground highly susceptible to erosion. There are approximately 15 acres of managed woodland on slopes over 6% on the UNC-CH campus. At slopes 6% or above, sufficient kinetic energy is held in the moving water to erode non-structural channels, and the bare ground of this cover type is even more susceptible to soil erosion.

Mulched planting beds cover over 43 acres on the campus with 10.6 acres on slopes over 6%. These areas vary in character, but typically represent familiar horticultural standards of trees, shrubs and herbaceous plants, sitting in lawn or in beds at the edges of a building. These planting beds could be designed and graded to receive run-off from the surrounding lawn or impervious areas. Planting beds with densely planted vegetation and little visible mulch would help to reduce run-off.

Rough grass is essentially a weedy and poorly maintained lawn. The cover is often discontinuous and in places may be very sparse with exposed bare soil. This type generally occurs in areas which were formerly turf, but have deteriorated due to lack of maintenance or poor soil conditions. The species present may be a mix of turf varieties, familiar lawn weeds, desirable and undesirable native grasses and in some cases, wildflowers.

This cover type cannot be maintained in good condition, because it is suspended between two vegetation types – turf which requires mowing and alteration of native soils and native grasses which are intolerant of frequent mowing and favor existing soil conditions. In virtually all cases, rough grass should be converted to another cover type.

Lawn is the most generally used ground cover on campus, regardless of soil type or slope conditions. Lawn varies in the amount of runoff it produces. Lawn with hard, bare, spots, lawn grown over compacted soils, or lawn on steep slopes have a very high co-efficient of runoff approaching 80%. On the UNC-CH campus there are approximately 27 acres of lawn on slopes over 6%. Replacing lawn on slopes over 6%, with forest, woodland or meadow, will significantly reduce runoff and trap sediment.

Managed shade lawns cover 126 acres or almost 17% of the campus. In the historic core they are the quadrangles of McCorkle and Polk Place. At present, the soils of these historic quadrangles and other smaller lawn areas are heavily compacted. Soil compaction occurs when weight on the soil surface–such as repeated foot or vehicular traffic—collapses the spaces in the soil where water, air and soil organisms can move, creating a hard solid non-living mass. Heavily compacted soils act as a barrier to root growth, inhibit the exchange of atmospheric gases and restrict the infiltration of water. Significant recharge cannot occur unless the compacted surface layer is broken through and is reestablished with a porous substrate. A change in turf management or a change in cover type would reduce stormwater impacts.

Table 2-2. EXISTING LAND COVER ON THE UNC-CH CAMPUS

PERVIOUS LAND COVERS AREA (ACRES) Forest 229.7 Managed Woodland 24.3 Planting Beds 43 Rough Grass 7.1 Lawn 126 Grass playfields 12.1 Sub-total 442.2

IMPERVIOUS LAND COVERS Buildings 101.2 Road/Parking surfaces 121 Pathways & Rec. Area 74 Open water 1.5

Sub-total 297.7

TOTAL 739.9

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Figure 2-32 “Sedimentation is the number one contaminant of surface water in the state.” (North Carolina Department of Environment and Natural Resources)

2.5 EROSION AND SEDIMENTATION CONTROL

As the campus develops over the next decade with numerous construction sites covering over fifteen percent of the campus, the receiving waters of the University such as Meeting of the Waters and Morgan Creek are particularly vulnerable to increased sediment load during the construction period. A high standard of Erosion and Sedimentation Control guidelines, rigorous plan reviews, enforcement and site inspections are essential to reduce the sediment loads that will cause severe impact to receiving waters.

All University projects regardless of their size must submit erosion and sedimentation plans to the University for review. The University has hired an additional employee to assist with review of construction, site erosion and sediment control plans as well as to inspect construction sites to review site erosion and sediment control measures and require their correction where necessary.

2.6 TREE PROTECTION REQUIREMENTS

Tom Bythell, University Forester, at the UNC-CH Facilities Services, has developed a Tree Protection Policy which includes tree protection measures and the requirement that any Project Landscape Architect, or any consultant providing A&E services, or the designer of any capital improvements, submit a Tree Protection Plan as part of the construction document package.

This plan must include: • Plan of all trees and shrubs on the site.• Description of protective measures and who will install and maintain them.• A description of all tree and landscape impacts especially from utility connections.• A description of all proposed impacts to trees and their root zones.• Locations, species and diameter of trees to be removed.• Locations, species and diameter of trees to be protected.• Locations and descriptions of protection measures, especially root zones.

The office of UNC-CH Facilities Services provides a slide show on Tree Protection as well astt Design and Construction guidelines.

Beyond protection of important site vegetation (before, during and directly after construction) the following guidelines are recommended:

• Identify all sensitive environmental areas on each site especially swales and natural drainage features.

• Use silt fencing to protect drainage swales and steep slopes from erosion. Place construction fence just above the break of the slope and use the fencing to prevent dumping and trespassing by vehicles and people.

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W AT E R B A L A N C E M O D E L A N A LY S I S

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3.0 WATER BALANCE MODEL ANALYSIS

The Water Balance Model (WBM) was used as a planning tool to analyze and evaluate the impacts of site development and to estimate and compare the volume of stormwater runoff and the amount of pollutants generated for both the existing conditions and for the Eight-Year Development Plan.

The model was then also used to evaluate the benefits of various proposed stormwater design solutions or Best Management Practices (BMPs) recommended to reduce volume and rate of stormwater, reduce NPS pollutants and resolve flooding issues. The goal was to allow the University to quantify development impacts and demonstrate regulatory compliance to both the Town and State, as well as to help the University in developing the most cost-effective and best performing methods to manage stormwater in a sustainable manner.

3.1 METHODOLOGY

The WBM first evaluated the current stormwater conditions and then compared these conditions to the “build-out” scenario of the Eight-Year Development Plan. Land use data and a Geographic Information System (GIS) base were developed for the UNC-Chapel Hill campus from the 1998 aerial photographs. In the development of the Town of Chapel Hill OI-4 Zoning Ordinance, the Town determined that the 1998 aerial photographs would represent “existing” conditions. Data used also included development projects that were in design, although not necessarily built, when the ordinance was adopted in August, 2001.

The existing land cover was classified into nine different categories—six pervious and three impervious—as shown in Table 3-1. Because these categories were used for the modeling, they are fixed. Table 3-1.

Classification of existing land cover on the UNC-Chapel Hill campus PERVIOUS Forest (with understory on Hydrologic Group B soils) Managed Woodland (with cleared understory) Planting Beds Meadow Areas Rough (unmaintained) grass Maintained lawns and grass playfields

IMPERVIOUS Building rooftops Roads and Parking Areas Pedestrian Paths and Recreational Areas

Figure 3-1 EXISTING UNC-CHAPEL HILL CAMPUS (July 2001)

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Future conditions, representing full build-out of the Eight-Year Development Plan (based on detailed project plans when available or Master Plan “footprints” for proposed projects) were compared to the model evaluation of the present campus.

For both existing and future conditions, the Water Balance Model considered three different sets of hydrologic conditions. The one-inch (1”) 24-hour storm event was evaluated to consider the impacts on the Town water quality regulations. The 2-year, 24-hour storm event of 3.6 inches was evaluated to determine the increase in the volume of stormwater runoff from development. Finally, the total annual rainfall of approximately 46 inches per year was evaluated to determine compliance with State water quality regulations.

The WBM evaluated the present and future campus on a watershed basis, by examining the five different watersheds at UNC-Chapel Hillapel Hill (Figure 3-1). In addition to the comparing the “before” and “after” effects of development on runoff volume and water quality, the Water Balance Model was also used to compare the effects and benefits of various BMPs including land cover changes. Various BMPs were considered at numerous locations throughout campus, and the benefits of proposed BMPs, both structural and non-structural, were measured and finally, the associated costs were compared. Detailed Output Tables for each of the watersheds are included in Appendix A.

Findings

The WBM analysis revealed four important findings:

1. Despite the number of projects planned, there is little increase in the total amount of impervious area under the Eight-Year Development Plan as shown in Table 3-2 (approximately 6.5 acres). This is because development largely occurs in areas that are already impervious. This is significant from a stormwater perspective because the total volume of stormwater runoff does not significantly increase, as seen in Table 3-3.

2. The amount of forested areas and woodlands decreases by 27 acres, while the amount of lawn increases by 30 acres. This has important ramifications for the aesthetic and environmental quality of the campus. An increase in lawn can also translate into an increase in fertilizer application and pollutant load. The loss of forest has implications for managing stormwater because forest areas infiltrate and clean water, reducing volume of runoff and pollutants.

3. With regards to water quality, the results are surprising. The amount of pollutants in stormwater from the Eight-Year Plan actually decreases (Table 3-3). This is because of a decrease in the acreage of parking lots which are a significant source of pollutants and an increase in the amount of roof areas which are relatively clean. This difference is enough to offset the damaging water quality impacts of the loss of 27 acres of forest and woods (Table 3-4).

4. In all cases, stormwater volume reduction by sub-basin, will exceed regulatory requirements if all the proposed BMPs are implemented. In Meeting of the Waters watershed (ME), the overall potential to reduce runoff volume significantly exceeds that required for compliance with the Town criteria. Some of this potential is found in the eastern-most tributary of the watershed (ME-3), where the athletic fields are located. The central portion of the watershed includes several major new structures—Rams Head Plaza and Ehringhaus Field—that are being constructed with BMPs that will provide significant post-development volume reduction.

Table 3-2. Changes in land use between existing conditions and the Eight Year Development Plan land use type existing 8 year differences conditions plan (acres) (acres) (acres)PERVIOUSForest 230 209 -21Managed Woodland 24 18 -6 Planting Beds 43 36 -7Meadow Areas 0 0 0Rough grass 7 4 -3Lawns and playfields 138 168 +30

IMPERVIOUSRooftops 101 126 +25Roads and Parking Areas 121 100 -21 Pedestrian Paths + Recreational Areas 74 77 +3

Table 3-3

Changes in pollutant loads between existing conditions and the Eight Year Development Plan

pollutant load existing 8 year differences conditions plan (lbs/yr) (lbs/yr) (lbs/yr)

Total Suspended Solids 296,997 256,748 -40, 249Total Nitrogen 2,678 2513 -165Total Phosphorus 1,808 1651 -157

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Table 3-4

INCREASE IN IMPERVIOUS COVER WITH THE EIGHT-YEAR DEVELOPMENT PLAN

WATERSHED TOTAL AREA IMPERVIOUS COVER EXISTING EIGHT YR. (Acres) (Acres) MEETING OF THE WATERS 441.3 215.3 219.0

MORGAN CREEK 49.9 22.2 24.6

CHAPEL 78.1 6.9 6.9

BOLIN 30.9 16.3 16.6

BATTLE 139.9 35.6 35.6 TOTALS 739.9 292 298.2

NET CHANGE 6.2 AcresPERCENT CHANGE 0.02% Increase

Table 3-5.

2 –YEAR STORM VOLUME COMPLIANCE with CHAPEL HILL SW ORDINANCE

WATERSHED DRAINAGE EXISTING 8-YEAR MITIGATION AREA RUNOFF RUNOFF VOLUME VOLUME VOLUME REQUIRED (ACRES) (CF) (CF) (CF)

MTG. OF 441.3 3,416,740 3,554,898 138,160THE WATERS

MORGAN 49.9 363,442 394,425 32,670

CHAPEL 78.1 283,050 282,980 0

BOLIN 30.9 279,857 282,980 3,630

BATTLE 139.9 688,500 688,653 150

RUNOFF VOLUMES AND POLLUTANT LOADS

While the GIS base provides an estimate of the potential land cover changes, the critical information is the volume of runoff and t amount of pollutants generated by these changes. The USDA Soil Conservation Service “Cover Complex Method” was used to calculate the response of each different cover type to precipitation. Curve numbers (CN) based on land cover type are determined and used to calculate runoff volume. CN values range from a low of 55 for a mature forest (the land cover type which generates the least runoff) to a high of 98 for impervious surfaces, (where runoff is almost total). CNs reflect both land cover type and soil type but they are empirical parameters based on research and observation. There are limits to the accuracy of these numbers and interpretation requires professional judgment.

Soils on the UNC-Chapel Hillapel Hill campus were probably originally Hydrologic Soil Group “B”. However, years of compaction and re-grading has certainly altered their natural drainage capacities and it would be safer to assume that most soils on campus should be classified as Hydrologic Group “C” or worse (including many areas of forest). Forest soils can only be assumed to be Hydrologic Group “B” where the land has been largely undisturbed.

The CN value is also important in evaluating the effects of recommended landscape changes. Converting land from one cover type to another more pervious one for example, converting lawn to meadow or planting beds, will result in a landscape that produces less runoff. The CN value serves as the parameter to estimate this effect, with the lower the CN the less run-off. If the University builds on a forest with a low CN the difference between the CN for built and undeveloped site is large. With a greater CN there is less of a difference, so that a lower CN represents a more conservative approach. Again, these curve numbers were used for modeling the University in this project, and cannot be changed.

Table 3-6

TYPICAL CURVE NUMBERS (CN) FOR LAND COVER ON THE UNC CAMPUS PERVIOUS Forest (with understory on Hydrologic Group B soils) 55 Managed Woodland (with cleared understory) 65 Planting Beds 70 Meadow Areas 74 Rough (unmaintained) grass 74 Maintained lawns and grass playfields 79

IMPERVIOUS Building rooftops 98 Roads and Parking Areas 98 Pedestrian Paths and Recreational Areas 98

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This map illustrates the spatial distribution of surfaces that generate the greatest amount of total phosphorus, with the highly fertilized play and athletic fields contrasting sharply with rooftops, where little phosphorus is generated.

In addition to determining the volume of runoff generated, the amount of pollutants generated was also estimated. Pollutant concentration values were developed for each land cover type based on an “Event Mean Concentration” value, or EMC. This value represents the average concentration of a pollutant, in milligrams per liter, that is generated from a given land cover type. Pollutants considered were; total suspended solids (TSS), total nitrate and nitrite, total phosphorus (TP), and the metals lead (Pb), copper (Cu), zinc (Zn), and total petroleum hydrocarbons.

Land cover directly impacts water quality. Roads generate more suspended solids than roof tops, forests generate less nitrogen than planting beds. Like the CN values, the pollutant rates (or EMC values) are based on literature and research. Much of this research has been conducted over the past thirty years at the federal level, or at a state or University level by the Environmental Protection Agency (EPA) or by Federal Highway Administration (FHA). The values selected represent the best available research at this time. As water quality data is developed for UNC-Chapel Hillapel Hill, the assumed values can be adjusted.

3.2 POLLUTANT GENERATION AND TRANSPORT

Various types of impervious surfaces will generate greater or lesser concentrations of pollutants, and these differences are included in the analysis of the mass transport of sediment conveyed by runoff.

The application of the Water Balance Model in the evaluation of pollutant transport is a complex process, since it does not trace the movement of a given raindrop through the drainage system, but rather replicates the observed change in stream level during a flood. NPS pollutants are a highly variable mixture. While the mix of pollutants will vary with land cover type, pollutants move in association with or attached to particles—as suspended solids or as dissolved solutes.To understand the movement of particulate and dissolved pollutants in runoff requires a discussion of the various components of Non-Point Source (NPS) pollution.

PARTICULATES

Storm runoff scours and suspends many pollutants as particulates, which are flushed from the surface of rooftops, pavements and roads. Pollutants transported as particulates include total phosphorus, organic matter, organic nitrogen, metals and some herbicides and pesticides.

“FIRST FLUSH”

Researchers have identified the effect known as “first flush” by analyzing the water quality samples over the duration of a storm. Concentrations of oil, solids and other pollutants accumulate between storms and water washing off during the early period of a storm has been found to have a higher concentration of pollutants This concentration washing off in the early part of a storm is known as “first flush”. It is often the “dirtiest” i.e. most polluted water, as documented by numerous studies. Figure 3-2 NPS POLLUTION, PARTICULATE TRANSPORT OF PHOSPHORUS (July 2001)

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Stormwater managers adopted the concept that 90% of the annual stormwater pollutant load was transported in the first half inch of runoff from all surfaces. New research suggests that the “half-inch sizing” rule may not be an adequate design criterion for sites with high impervious cover. These sites may require capture of a stormwater volume of one or more inches, to prevent washing away the “first flush” before it can be treated or infiltrated. This new thinking is the basis of the Town and State regulatory requirement to treat the first one inch of run-off.

POLLUTANT TRANSPORT

Most of the NPS transported during a storm, occurs during the relatively short spans of heavy rainfalls which total only about 25 to 30 days a year. This is especially true for pollutants transported by or associated with particulates, especially colloids. These particles, such as clay soils, are so small that they do not settle, and instead remain in suspension for several days and are carried through the system by stormwater. It is possible to add chemicals to a stormwater basin to coagulate these colloids so that they settle, but this turns a stream channel or pond into a treatment area, and removes sludge required for a natural system to function.

To accurately measure the amount of particulates transported during a given storm, both volume and concentration must be measured simultaneously. To fully develop this information for a watershed, a number of storms must be measured over several years. Dry weather chemistry is seldom indicative of expected wet weather concentrations, which can be two or three orders of magnitude greater.

SOLUBLE POLLUTANTS

Several types of NPS pollutants are soluble, or quickly become soluble in runoff. These include nitrates, ammonia, salts, many pesticides as well as hydrocarbons. While the load increases in heavy storms because the heavier volume of water scours more pollutants from the land surface, the concentration of pollutants will actually decrease as they are diluted over a given storm. The current regulatory requirement defines a “total maximum daily load” (TMDL) for a given pollutant. Although these requirements are complicated by measurements in wet and dry weather conditions, the total amount of pollutants carried by runoff is significantly greater in wet weather and represents the major portion of the total annual discharge, whereas dry weather sampling reflects the steady discharge of soluble pollutants into the stream flow.

Table 3-7 summarizes the amounts of particulate and soluble pollutants assumed to be in the average concentration of stormwater from the campus. Some NPS pollutants are enter the system from the precipitation, especially downwind of industry using fossil fuels. Paved surfaces also generate nitrogen load, derived from a mix of sediment, animal wastes and human detritus of many different forms. Lacking any current data for the stormwater runoff chemistry from the UNC-Chapel Hill Campus, other sources of representative NPS concentrations have been used for the initial water quality model analysis. The table summarizes the “Event Mean Concentrations” for stormwater runoff, expressed in milligrams per liter (mg/l). They reflect the wet weather transport mechanisms and estimate mass transport during runoff, based on the volume and the mean concentration value.Figure 3-3 NPS POLLUTION, SOLUBLE NITRATE (July 2001)

This map illustrates landscapes generating nitrogen on campus showing the highly fertilized athletic fields as a major source followed closely by fertilized lawns.

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Figure 3-4 WATER QUALITY MONITORING SITES (July 2001)

Table 3-7.

WET WEATHER EVENT MEAN CONCENTRATION (mg/l)

LAND COVER POLLUTANT Total Suspended Total Nitrate COD TPH Lead Copper PSolids(Mg/l) (Ug/l) (Mg/l) (Mg/l) (Mg/l) (Mg/l) (Mg/l)

PERVIOUS SURFACES Forest 40 145 0.25 40 0 0.0015 0.008Managed Woodland 40 145 0.25 40 0 0.0015 0.008Planting Area 150 1,000 0.90 53 0 0.005 0.01(Fertilized)Rough Grass 78 1,250 1.10 53 0 0.005 0.01Lawn 100 1,500 1.30 60 0 0.005 0.01(Fertilized)Playfield 120 1,900 1.70 65 0 0.005 0.01(Fertilized)

IMPERVIOUS SURFACES Building Rooftops 1 80 0.34 1 0.6 0.0027 0.024Roads & parking 135 430 0.83 85 9.0 0.011 0.047Paths & Recreation 60 190 0.50 50 0.4 0.009 0.014

Sources:1) Results of the Nationwide Urban Runoff Program, U.S. EPA2) Pollutant Loadings and Impacts from Highway Stormwater Runoff, FHWA (1990)3) Characterization of Non-point Sources and Loadings to Corpus Christi Bay (1996)4) Technical Note #105 - Watershed Protection Techniques (1997)5) Center for Watershed Protection (Design of Stormwater Filtering Systems – (1995)

FLOW MONITORING

Analyzing pollutant loads was the starting point for evaluating stormwater management practices on the UNC-Chapel Hill campus. This information was used to determine the potential NPS load from the Eight-Year Development Plan. As site specific data is gathered, the values used can be modified to refine model assumptions.

The Department of Environment, Health and Safety at UNC-Chapel Hill is presently conducting a stream sampling program. This accumulating record will provide a database for future management decisions and a measure of the success of the mitigation measures implemented. The most useful information should come from data collected at the monitoring station on Meeting of the Waters Creek.

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Figure 3-5 EIGHT-YEAR DEVELOPMENT PLAN LAND COVER (July 2001)

Table 3-8

SAMPLING DATA COLLECTED AT MEETING OF THE WATERS STATION (Sample dates 11/14/2000, 9/02/2001 and 9/10/2001)

Parameter Flow Condition Range of Concentrations

Suspended Solids dry 1.2 to 12 mg/l Total Phosphorus dry 180 to 400 ug/l Nitrate dry 0.98 to 1.18 mg/l Total Nitrogen dry 1.36 to 3.14 mg/l Oil & Grease dry 0 to 6.3 mg/l

It is hoped that data from major storms will confirm assumptions in this report about the pollutant loads. While the current data is preliminary, Table 3-8 shows representative concentrations for selected pollutants and indicates that some pollutants, such as Total Phosphorus, are significantly higher during dry weather periods. This suggests that wastewaters are finding their way into the storm drains. Low levels of herbicides are also found at a number of locations, suggesting runoff from lawns and horticultural landscapes.


In the Eight-Year Development Plan, due to the increase in the total volume of runoff, various Best Management Practices (BMPs) will be needed to reduce this increase and comply with the Town of Chapel Hill Ordinance. These BMPS can also serve to reduce the amount of pollutants discharged from the campus.

In the 2001 Campus Master Plan, general stormwater management concepts to reduce the impacts of increased runoff volume and NPS pollution were proposed. These included restoration of the “natural drainage system” of streams and swales, construction of new infiltration systems, and re-vegetation of specific areas of the campus particularly the steep slopes. In the older portions of the campus, problems of localized flooding may be solved by providing temporary storage to manage the rate of runoff at critical and hydraulically overloaded junctures in the storm sewer piping.

With this Stormwater Management Plan, a more detailed set of stormwater management strategies has evolved, focusing on what might be accomplished within the development footprint of each given project. Most of the measures considered represent new methods and materials now being explored as ways to better manage stormwater. Some measures previously considered are difficult to apply on the existing UNC-Chapel Hill campus, but may warrant reconsideration in the future. In the final chapter of this report, a number of Case Studies/Pilot Projects describe the specific application these BMPs types. Specific applications include BMPs already include part of projects built over the last two years as well as those in design or proposed for design consideration.

The following chapter discusses in detail the various BMPs that have been considered and quantifies both their volume reduction and water quality benefits. Solutions are described along a gradient—from the required to the possible. Many of their benefits of go beyond regulatory goals and set a high standard for the University.

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B E S T M A N A G E M E N T P R A C T I C E S

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4.1 BACKGROUND AND PURPOSE

A number of Best Management Practices (BMPs) or mitigation measures, have been considered to reduce stormwater volume, rate and water quality impacts resulting from development—both existing and planned—on the UNC-Chapel Hill campus. The Environmental Master Plan proposed general stormwater management strategies to reduce these impacts.

With this Stormwater Management Plan, a detailed set of stormwater management measures, uniquely appropriate to the UNC-Chapel Hill campus have evolved. These measures focus both on what can be accomplished within the footprint of each development project as well as campus-wide land management changes. A number of these programs are already in place and can, over time, significantly reduce the impacts from development. Most of the measures proposed are new methods now being explored throughout the country as ways to better manage stormwater.

This chapter describes generic recommended BMPs and examines their potential to meet both University needs and local, state and federal regulations. Chapter 5–the Stormwater Management Recommendations describes the actual BMPs proposed and those that have already been used on campus. Many of the benefits of these BMPs go beyond regulatory goals and set a high standard for the University.

4.2 RECOMMENDED BEST MANAGEMENT PRACTICES

The BMPs, recommended in this report can be divided into two general categories: structural and non-structural. Structural BMPs are built measures that physically provide volume reduction, rate control or pollutant removal. Non-structural measures include conversions of existing land cover types to reduce land surfaces with high runoff, as well as University-wide management programs, that help avoid or reduce pollutants before they enter the drainage system. Volume reduction measures proposed will also reduce flow rates during heavy storms and mitigate flooding concerns.

The BMPs proposed vary widely and do not always lend themselves easily to direct comparison. However, two key criteria—reduction of runoff volume during design rainfalls and reduction of selected Non Point Source pollutants—can serve as measures of their effectiveness. The BMPs discussed in this chapter were chosen after considerable discussion with the University representatives as those appropriate for the UNC-Chapel Hill campus. These measures are summarized in Table 4-1 and their proposed locations are shown on the map of the campus Figure 4-1. Table 4-1 also lists other measures not presently part of the overall campus-wide stormwater management strategy, such as “daylighting” of historical streams, creation of riparian buffers, retrofits of detention basins and intensive wetland treatment systems which were suggested in the Environmental Master Plan and which may prove useful in the future.

The following discussion of each BMP is intended to offer a comprehensive description without providing full design specifications. Final designs will vary depending on specific field conditions.

Figure 4-1. PROPOSED LOCATIONS OF ALL BMPS ON THE UNC-CHAPEL HILL CAMPUS

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Table 4-1.

BEST MANAGEMENT PRACTICES FOR THE UNC-CHAPEL-HILL CAMPUS

STRUCTURAL BMPs

Permeable Pavement with Storage/Infiltration Other Surfaces with Storage/Infiltration Vegetated Roof Systems and Roof Gardens Water Quality Inlets Rain Gardens Tree Trenches Runoff Capture and Re-use Systems Ponds and Wetlands Storage/Treatment

NON-STRUCTURAL BMPs

Reduction in Chemical Application Street Cleaning by Vacuum Removal Land Cover Conversions Stormwater Management Education Illicit Discharge Detection and Elimination

ADDITIONAL MEASURES NOT INCLUDED

“Daylighting” of Historical Streams Creation of Riparian buffers Detention Basin Retrofit Intensive Wetland treatment systems

4.3 STRUCTURAL BMPS

The structural BMPs considered vary greatly in efficiency, cost and overall applicability depending on their actual site location, but all require construction or installation. The most effective measures are applied in the uplands, near the sources of runoff (impervious surfaces). Located at the source, they are able to reduce the amount of runoff, the rate of flow and the kinetic energy of the storm water that scours and transports pollutants.

PERMEABLE PAVEMENTS WITH STORAGE/INFILTRATION BEDS

Permeable Pavements with Storage/Infiltration Beds have been used in a number locations throughout the country as shown in Fgure 4-2, on a map of the United States.The pavement most used is permeable asphalt. The North Carolina Department of Transportation (NC DOT) has a specification for an open-graded asphalt mix that is used as a thin (0.5”) topping on impermeable roadways to prevent “hydroplaning”. Permeable pavements may also be constructed with an open graded concrete. Examples of projects built in similar climatic conditions can serve as comparables for this BMP, since there has been limited local experience with permeable paving with storage/infiltration beds.

Figure 4-2 MAP OF THE UNITED STATES SHOWING LOCATIONS OF PERMEABLE PAVEMENT INSTALLATIONS (Source: Cahill Associates)

Permeable Concrete has been in use for over a decade, in the sandy soils of Florida.Here, the pavement is laid without a sub-grade storage bed and rainfall infiltrates directly as the soils are highly absorbent. UNC-Chapel Hill is located in the Piedmont, with heavy clay soils. There are concerns from the local engineering community that water will not be able to infiltrate through the stone storage/infiltration bed beneath the pavement into these soils. The two systems built at UNC-Chapel Hill and described below have not produced any surface runoff, even during recent heavy rainfalls (September 2004).

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The function of the underground bed is to infiltrate rainfall slowly (or in some cases rapidly) into the soil, where it moves into and recharges the water table. The slower the movement of water into the soil, the greater the storage capacity required and therefore the deeper the underground bed required as part of this system. The volume reduction benefits are shown in Table 4-2. Representative costs for 2002 are shown in Table 4-3.

Table 4-2

VOLUME REDUCTION BENEFITS FOR STORAGE/ INFILTRATION BEDS

Rainfall Event inches/sf of BMP cf/sf of BMP Assumptions

1” Rainfall 2.0” 0.17 BMP stores total runoff volume of 1” rainfall and 1” of additional runoff conveyed from

surrounding areas.

2-Year Storm (3.6”) 7.2” 0.6 BMP stores total runoff volume of 2-year storm and equal volume of runoff conveyed from

surrounding areas.

Annual Precipitation (46”) 87.0” 3.67 It is assumed here that this BMP can store the total run-off volume of 1 inch of rainfall falling directly on the surface and 1 inch of rainfall from surrounding areas and that this water subsequently infiltrates into the soil, picking up runoff from adjacent continuous surfaces.

Table 4-3 (Please note cost assumptions date from 2002)

COST ASSUMPTIONS: PERMEABLE PAVEMENT WITH STORAGE/ INFILTRATION BEDS

ITEM $/SF

Demolition and Earthwork $4.00Permeable Asphalt Paving (2.5”) $0.50 (The cost of Asphalt is about 25% less than Concrete. This cost differential occurs, in part, because the pavement is thinner (2.5” versus 6”).Stone and Geotextile Fabric $3.00 Piping and Stormwater Structures $0.50

Total $8.00

This system—Permeable Pavements with Storage/Infiltration Beds—has been recently used at UNC-Chapel Hill for a 600-car facility addition to the existing Estes Drive Remote Lot, and for a 750-car parking lot adjacent to the Friday Center, south of the campus. In these demonstration projects both permeable asphalt and concrete pavements were used. Soils at the Friday Center had a greater clay content and in this case the lot was designed with a deeper bed. In addition, the upper layer of heavy clay soil was removed in some areas. The slow movement of water through the underground beds, then into the soil, also filters pollutants from the stormwater.

The capacity of this type of BMP to store and infiltrate significant volumes of runoff and to limit transport of NPS pollutants is well documented (Guidance Specifying Management Measures for Sources of Non Point Pollution in Coastal Waters, January 1993 United States Environmental Protection Agency #840-8-92-002: National Pollutant Removal Database for Stormwater Treatment Practices, June 2000, Winer, R., Center for Watershed Protection, Ellicot, MD). Where conditions are suitable, this is the BMP that most effectively reduces volume, however, volume reduction can only be achieved where infiltration actually occurs.

A major constraint in using this BMP is the capacity of the soils to infiltrate. Of the 46 inches of average annual rainfall, only 4-6 inches per year actually infiltrates. The Soil Survey for Orange County, June 1977, describes the majority of soils underlying the UNC-Chapel Hill campus as “moderately well-drained”, except for those in floodplains. However, almost all of these soils are classified as Hydrologic Soil Group C or D, except for the soils in the historic campus core. These soils on the plateau, are classified Hydrologic Soil Group B and theoretically should infiltrate without problem. In addition, although the soils at UNC-Chapel Hill have a high clay content and have been compacted, infiltration does occur in some locations, even if very slowly. If there were no infiltration, all the campus streambeds would be dry when it did not rain. Beyond the main campus, where the same fundamental soil types are less disturbed, there may be a greater potential for large-scale infiltration.

A second constraint in using this BMP on the main campus is the lack of opportunity. Many of the existing large surface parking lots on campus are scheduled to be replaced by buildings or parking garages and while several surface lots will remain during the buildout of the Eight-Year Development Plan and are possible candidates for reconstruction many of these will be replaced by structures in the long term. Therefore, in the Stormwater Management Plan, only a few main campus locations are identified for this solution (Figure 4-1).

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Figure 4-3 PHOTOGRAPH OF A PARKING LOT WITH STORAGE/ INFILTRATION BEDS BENEATH, BUILT IN 1986, SHOWING CONVENTIONAL ASPHALT IN THE ROAD AND PERMEABLE ASPHALT IN THE PARKING BAYS.

Figure 4-4 THE SECTION SHOWS THE STORAGE/ INFILTRATION BEDS BENEATH THE LOT.

Figure 4-5 DIAGRAM OF STORAGE/ INFILTRATION SYSTEM WHERE WATER IS STORED IN LARGE PIPES RATHER THAN STONE BEDS AND GRADUALLY RELEASED TO THE SOIL MANTLE THROUGH INCREASINGLY SMALLER PIPES.

There has been some concern that the infiltration of stormwater will be in violation of the NC division of water quality rules regarding underground injection wells. During the 1970s, the use of deep injection wells for the disposal of waste water effluent including some industrial discharges was given consideration and some systems built with negative impacts. Many states then developed regulations to prohibit use of ground water aquifers as receiving water bodies. Infiltration of rainfall is very different issue, but the question of sub-surface pollutant migration is a valid concern. There has been much discussion of stormwater infiltration systems falling under this prohibition, especially in coastal states with unconsolidated sub-surface formations, vulnerable to contaminants. The resolution of this issue, is to use the cat-ion capacity of the soils as a guide to pollutant removal efficiency, with coastal sands requiring additional organic materials at the bottom of the infiltration bed. Projects in the coastal sands of New Jersey have followed this design and overcome concerns. At UNC-Chapel Hill, these concerns are not an issue, as all soils on campus have a cat-ion capacity greater than 10.

STORAGE/INFILTRATION BEDS UNDER OTHER SURFACES

A number of areas on campus, besides parking lots, are potentially suitable for the construction of storage/infiltration beds, to hold and where possible infiltrate stormwater. Athletic Fields, Intermural Play Fields and Recreation Areas are all facilities that could be underlain by this BMP. The surface in this case is most likely to be turf, but can also be an impermeable surface such as artificial turf, that drains to a sub-surface stone infiltration/storage bed (Figure 4-4). However, for UNC-Chapel Hill to take credit for volume reduction in a given rainfall, the underlying soil must either allow infiltration of the stored volume or there must be quantifiable re-use of the stored water. The stormwater cannot simply be held as detention storage.

Figure 4-6 AERIAL VIEW OF CARMICHAEL FIELD BEFORE CONSTRUCTION OF STORAGE/ INFILTRATION BEDS.

The soils on any proposed site must be evaluated to determine feasibility. Evaluation must include testing at a number of locations within the proposed bed footprint. Final bed bottom elevations are controlled by the most suitable horizon for infiltration. The original Carmichael field design included a 36-inch deep, uniformly graded stone storage bed. In the final design the bed was dug deeper to remove polluted fill. Based on this design, volume reduction could be as great as 14.5 inches of rainfall stored and slowly infiltrated (40% of a bed depth of 36 inches).

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Sub-watershed ME-3 is the location of a number of Athletic Fields and Intermural Fields, some of which have been built with synthetic surfaces and under-drained, while others are partially paved with impervious surfaces, such as a running track. Several others remain in turf or other permeable surfaces. Some of these fields have been built on extensive fill and heavily compacted. For example, the recent excavation for the stone infiltration/storage bed at Carmichael Field revealed the original stream and floodplain at 12 feet below existing grade. Existing storm sewers running through many of the fields also create design complications. Located at the lower end of sub-watershed ME-3, where upland runoff can be intercepted, Bosheimer Field is a possible candidate for such a sub-surface bed. Representative costs for this BMP are shown in Table 4-4.


COST ASSUMPTIONS FOR INFILTRATION/STORAGE BEDS UNDER OTHER SURFACES

Item $/SF Demolition and Earthwork $3.50 Stone and Geotextile $3.00 Piping and Stormwater Structures $0.50

Total $7.00

Note: Surface restoration costs will vary with choice of surface (turf, artificial turf, etc.) and are not included in this table.

Figure 4-7 PLAN AND DIAGRAM OF STORAGE / INFILTRATION SYSTEM FOR CARMICHAEL FIELD

RUNOFF CAPTURE AND RE-USE SYSTEMS

Several runoff capture and re-use systems offer the opportunity to hold significant amounts of direct rainfall from roof areas that do not lend themselves to a green roof system (Figure 4-8). Since roof runoff is less polluted than street or pavement runoff, this water can be used as a source for a variety of non-potable needs. Collected rainfall from garage roof decks is generally not suitable for use without further pollutant removal. For larger commercial or industrial buildings, vertical storage units of large (24” plus diameter) pipes can be incorporated into the roof drainage system (Figure 4-8 and Figure 4-9). Captured rooftop runoff can also be stored in basement structures, but this requires re-use of the rainfall before the next storm and energy to pump the stored water.

A two-level control structure or “weir” can be used to allow the initial “first flush” to bypass the storage system. In addition, a filter should be used to prevent leaves and debris from entering the storage tank.

The Chapel Hill Town Ordinance O1-4 states that post-development runoff conditions will either draw down the runoff volume to the pre-storm design stage within 5 days or the post-development discharge rate will be no larger than the predevelopment discharge rate for the 1-year frequency, 24-hour duration storm event (3.00 inches). It is suggested that all campus runoff capture and re-use systems be designed so that they are emptied every 72 hours and are therefore prepared to receive the next storm.

Figure 4-9 SECTION OF CISTERN CAPTURING ROOF WATER WITH RE-USE FOR IRRIGATION

Figure 4-8 PICTURE OF BUILDING WITH CISTERNS FOR CAPTURING ROOF WATER WITH RE-USE FOR IRRIGATION

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Captured rainfall can serve a number of re-use purposes, including irrigation, chiller system water (with some chemical clarification and ion removal) or other functions that would substitute for and reduce the use of treated water. This BMP can greatly reduce runoff volume in a sub-watershed that has few other opportunities, as well as reduce consumption of treated water. The variations for this BMP are quite different in both form and function, and require significant further design development before they can be considered as actual solutions. However, each offers the opportunity to incorporate stormwater benefits with site improvements that will enrich the campus in many other ways. In the more impervious portions of the campus, where vegetated roof systems are not feasible or desired, they provide the only possible volume reduction solution.

This BMP should not be confused with large pipe or tank systems placed below grade to detain runoff. These below-grade systems intercept runoff from all surfaces and require that NPS pollutants be removed if their water is to be re-used. Their purpose is to provide below grade detention, and they function like a surface detention basin. This detention basin must also be emptied before the next storm. Volume reduction for this BMP is shown in Table 4-5 and cost assumptions in Table 4-6.

Table 4-5

VOLUME REDUCTION BENEFIT—CAPTURE & RE-USE SYSTEMS

Rainfall Inches/sf of BMP cf/sf of BMP Assumptions

1” Rainfall 1.0” 0.083 BMP stores total runoff volume for the 1” storm.

2-Year Storm (3.6”) 1.8” 0.15 BMP captures 50%. of the 2-year storm

Annual Precipitation (46”) 32.0” Approx. 70% of annual of 46”average precipitation occuring in storm events equal or less than 1.8 inches.


COST ASSUMPTIONS FOR RUNOFF, CAPTURE & RE-USE SYSTEMS*

Item $/SF Storage (3.6”) and piping $3.45

Total $3.45

VEGETATED ROOF SYSTEMS AND ROOF GARDENS

Vegetated Roofs, used historically for centuries, have recently been adapted to modern buildings. This work is largely a response to the problem of stormwater runoff in highly urbanized communities, such as the German cities rebuilt after World War II,(Figure 4-10).

Figure 4-10 EXAMPLES OF SIMPLE VEGETATED ROOF SYSTEMS

A simple vegetated roof, sometimes called an “extensive vegetated roof system”, is a series of thin layers supporting a top layer of low growing, drought tolerant vegetation. In this system the roof slope cannot exceed 22%. The several layers are; a waterproofing layer, a root barrier, a drainage/storage layer, growth media, and the actual vegetation. It is assumed that a vegetated roof consists of a 2-inch drainage layer with 40% void space, 4 inches of growth media with a 20% water holding capacity, and vegetation.

Based on local climatic conditions, during the growing season, much of the rainfall is returned to the atmosphere as evapo-transpiration. Each square foot of vegetated roof can evapo-transpirate 1.7” of stormwater during the 2-yr storm, (Table 4-7). This BMP can be used both on new buildings as well as to retrofit existing ones. In Chapter 5, Stormwater Management Recommendations, a number of buildings at UNC-Chapel Hill are proposed as candidates for this BMP.

The simple vegetated roof not only returns up to 70% of the annual rainfall to the atmosphere as evapo-transpiration, it also reduces the production of CO2. Experience in Europe over the past twenty years confirms that the life of a building roof is doubled by adding a layer of vegetation that insulates and protects the roof materials from ultra-violet deterioration. In addition to the stormwater benefits, the extra layers on the roof can add substantial insulation benefits, reducing energy costs. These energy savings are not included as benefits in the tables, but can represent a significant savings in building operation costs.

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Table 4-7

VOLUME REDUCTION BENEFITS FOR VEGETATED ROOF SYSTEMS


1” Rainfall 1.7” 0.14 BMP stores runoff volume of 1” rainfall and 0.7” of additional runoff conveyed from surrounding areas

2-Year Storm (3.6”) 1.7” 0.14 BMP captures approx. 50% of the 2-year storm

Annual Precipitation 35.0” 2.92 Approx. 75% of the annual (46”) precipitation occurs in storms less than 1,7 inches.

The “intensive” Roof Garden is more complicated to design and build. It provides a landscape that includes everything from trees to ground covers and requires deep soils and must be integrated into the design of a building with significant added structure to support this type of roof. However, it can then give the University added recreational space and will increase the general sense of “green” in a dense urban environment.

Figure 4-11 shows an example of a multi-layer green roof, illustrating the additional space that can become available with a roof garden. If irrigation is required and the irrigation water provided from external sources, water from other impervious sources can be used for this purpose. This will increase the amount of stormwater volume reduction that this BMP can provide. If cisterns are constructed as a part of the roof design, they can capture and re-use any rainfall not held by the green roof itself. In these cases, the water holding tanks will increase the structural design requirements and therefore the cost.

Figure 4-11 AN EXAMPLE OF AN “INTENSIVE VEGETATED ROOF” OR “ROOF GARDEN”, SHINJUKU MITSUI, TOKYO, JAPAN.

Figure 4-12. SECTION SHOWING A GRADIENT OF TECHNICAL REQUIREMENTS FOR PLANTING EXTENSIVE AND INTENSIVE ROOF SYSTEMS.

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Both types of this BMP—simple green roofs and roof gardens—have been considered for a number of the buildings in the Eight-Year Development Plan (Figure 4-1). For buildings that are proposed, but not yet designed, these vegetated roofs are suggestions for review. However, for purposes of analysis, it is assumed that all of the projects identified as including a vegetated roof system as part of the final design, will actually include this BMP and this potential volume reduction benefit has been included in the evaluation of each sub-watershed.

A vegetated roof on a parking structure has the same stormwater benefits as on any other building, but in order to retain parking on the top deck, an ultra light structure over the deck to carry the vegetation could be used. A “Green Solar Canopy” (Figure 4-13), was suggested, possibly designed as a steel trellis with solar panels or film photovoltaics alternating with panels for low growing vegetation. Such a structure would be expensive if used only to capture and hold rainfall. However, if this canopy can also incorporate solar panels, the system could provide multiple environmental benefits, including alternative energy production, rainfall capture, volume reduction by evapo-transpiration, vehicle protection in bad weather, and “dark sky” benefits of reduced light pollution from conventional garage lighting. Such a variation on the simple vegetated roof system is suggested for the Cardinal and Dogwood decks of the Hospital Parking Garages.

It is understood that not all of the green roofs recommended will actually be installed, thoe presently considered for implementation are listed in Chapter 5.

Figure 4-13 A TYPICAL PARKING GARAGE ROOF AND PROPOSED “GREEN SOLAR CANOPY” FROM ABOVE VIEW OF CANOPY FROM BENEATH.

Table 4-8 Please note this cost assumption is current / 2004 and per square foot. COST ASSUMPTIONS FOR A SIMPLE VEGETATED ROOF SYSTEM (EXTENSIVE) Cost Details* Item Waterproofing Drainage Layer (4”) Growth Media (4-8”) Vegetation Piping, Geotextile, etc.

Total $7.00 - $12.00

Table 4-9 This cost assumption is current / 2004 and per square foot. Costs will vary significantly depending on the amount and size of vegetation used. Costs of additional structure are not included.

COST ASSUMPTIONS FOR ROOF GARDENS (INTENSIVE)

Cost Details* Item Waterproofing Drainage Layer (4”) Growth Media (18-36”) Vegetation Piping, Geotextile, etc.

Total $20.00 -- $25.00

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WATER QUALITY INLETS

This small BMP, although not very dramatic, can be inexpensive, easy to install, and provide significant water quality improvement, preventing trash and debris from reaching the stormwater system. However, this BMP does not provide volume reduction or rate control.

A box within the inlet structure captures detritus of all sorts, holding it for later removal. Everything from grass clippings and dead leaves to paper, animal wastes, and a mix of synthetic organic materials can be captured during the initial flush of runoff. (Figure 4-14) Small containers are installed in area drains and inlets or more elaborate structures retrofitted in larger existing inlet boxes. It is also possible to build large sub-surface containment chambers (Figure 4-15) which are very expensive but useful when there are no other options. These units must be cleaned and maintained every three months and maintenance costs can be considerable. If these inlet boxes are not maintained they are ineffective.

Figure 4-14 EXAMPLES OF SMALL WATER QUALITY INLETS

Figure 4-15 TYPICAL VIEWS: PLAN, PROFILE AND SECTION OF SUB-SURFACE CONTAINMENT CHAMBER.

Installing water quality inlets throughout the drainage system in large portions of the UNC-Chapel Hill campus—on streets, parking lots, plazas and lawns—can offer a substantial reduction in pollutant transport. These units must be cleaned on a regular basis to operate successfully, and the cost of maintenance, must be a part of the cost-benefit comparison.

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General Guidelines for Rain Garden Design

• Provide positive connection to Storm Sewer for Run-off Overflow.• Calculate retention and storage run-off volume based on both surface water and soil water-

holding capacity. • Survey existing conditions to avoid disturbance of existing vegetation and utilities.• Design depression so that standing water is held for no longer than 3 – 4 days to avoid

breeding mosquitoes.• Design Rain Gardens with tall grass buffers to slow run-off and to filter sediment from

overland flow.• Designs should include native plant species suited to seasonal fluctuations. Most flood

plain species are well adapted to Rain Garden conditions and will tolerate periods of water inundation as well as very dry conditions. Use plant material that tolerates longer periods of standing water in the lowest part of the depression.

• Test soil to determine specific site percolation rates.• Rain Gardens will require soil amendments. Excavation to create these features will expose

sub-soils that lack nutrients and organic matter to support new vegetationAmend soil, where necessary, to increase infiltration and water holding capacity.Incorporate soil amendments for the new plantings adding organic material, such as leaf mould or composted material (10%) mixed with sand (50%) and topsoil (40%). A soil pH of 5.5 to 6.5 is optimum for pollutant removal by microbial action.

• Cover soil in the planted areas with attractive pebbles to weigh it down and avoid use of floatable mulch.

The importance of this BMP as a stormwater mitigation measure is its ability to reduce retained volume by slow infiltration and evapo-transpiration. With the disturbed soils on campus, soil replacement may be necessary in some locations to foster plant growth and encourage infiltration or at least to increase the water holding capacity of the soils. Soil replacement will add to the cost of this BMP.

A volume reduction of 0.05” during the 2-year storm of 3.6” is assumed. Additional storage capacity is possible under optimal conditions with the use of a sub-surface storage and infiltration bed. If that storage and infiltration capacity were included, the volume reduction could be on the order of 1.8 inches for the 2-year rainfall, as shown in Table 4-10.

Figure 4-17 RAIN GARDEN

RAIN GARDENS

Rain Gardens are dispersed shallow planting basins generally 6 inches to 1 foot in depth. The planting areas can be any size or shape, but in the campus landscape it is recommended that the sites should be at least 1,000 square feet in size and located in areas that are less than 3% slope. Rain Gardens are planted with wetland vegetation—herbaceous plants, shrubs, understory and canopy trees. Areas that once were largely lawn or planting beds can also be converted to rain gardens. They can also be established in poorly drained areas, which are difficult to maintain as good lawn, as well as in open swales in parking islands. Cumulatively, use of this BMP could contribute significantly to the reduction of the impacts of current development. Rain gardens would not only reduce volume and rate but also improve water quality, effectively capturing and filtering pollutants, with their dense, deep-rooted vegetation and the action of associated micro-organisms, They may also provide a positive aesthetic contribution to the campus and an increase in campus biodiversity.

This BMP provides some rainfall retention and storage capacity, some evapo-transpiration from the plants and if the soils permit, some infiltration. Rain gardens can take many different configurations and readily adapt to a range of environmental conditions. Examples of this BMP are shown in Figure 4-16, Figure 4-17.

Figure 4-16 EXAMPLES OF RAIN GARDENS

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Figure 4-18 RECHARGE TRENCH DETAIL

Figure 4-19 REINFORCED CONCRETE OUTLET BOX

Figure 4-20 RAIN GARDEN CONCEPTUAL PLAN AND SECTION

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Table 4-10

VOLUME REDUCTION BENEFIT FOR RAIN GARDENS


1” Rainfall 1.0” 0.08 BMP soil medium has a moisture capacity of 15% of total soil volume capable of storing total direct rainfall for the 1” storm.

2-Year Storm (3.6”) 1.8” 0.15 Based on above estimate, the max. moisture capacity in one cubic foot of soil mix is 1.8”.

Annual Precipitation (46”) 32.0” 2.67 Approx. 70% of annual precipitation occurs in storm events equal or less than 1.8 inches.

Because the soils are typically slow to infiltrate on the campus, part of the cost of this BMP is a soil amendment to a depth of two to four feet for the planting zone. Under this zone it is important to install a perforated underdrain in a gravel bed connected to campus storm drains or to install a french drain as conditions suggest, to convey the excess water from extreme or back to back storms.

Construction of the rain garden can require grading to create a gentle depression. Ideally, this BMP will be strategically placed to intercept the first flush of run-off from adjacent impervious surfaces. Areas of turf and sparse horticultural plantings that now typically convey run-off by sheet flow to the stormwater infrastructure system can be converted to rain gardens. Cost assumptions are shown in Table 4-11.

Table 4-11 Please note cost assumptions date from 2002.

COST ASSUMPTIONS FOR RAIN GARDENS*

Item $/SFSoil Amendment $1.50Stone $3.00Vegetation $5.00Piping $0.50

Total $10.00

Tree Trenches

Where the campus has become increasingly urban, traditional street tree pits create manyproblems for trees. Street trees in pits suffer a variety of stresses including compacted soils,which restrict root growth, the necessary exchange of atmospheric gases and access to waterand nutrients. These pits often include toxic materials such as construction debris, salt, urine,and gases from leaky pipes. All of these factors impair tree health and reduce their chance forsurvival, (Figure 4-21).

Figure 4-21 TROUBLED URBAN ROOTS Tree Trenches are continuous planting strips, typically 2.5-3.5 feet deep, filled with a new soil mix. They provide adequate growing space for tree roots and also create opportunities to capture and even infiltrate stormwater. Tree Trenches can be continuous excavated areas that are open at the surface where existing soils are amended or covered with modular paving at the surface for light traffiic. A third variation back-fills the excavated area with a special structural soil mix for heavy traffic, (Figure 4-22).

Figure 4-22 CONTINUOUS TREE TRENCH ON URBAN SIDEWALK WITH MODULAR PAVING

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General Guidelines for Tree Trench Design • Where existing soil stays in place, the soils in the trench should be ameliorated to a depth of

3 feet the entire length of the trench.• For Tree Trenches under paved areas with heavy traffic provide a backfill with a structural

soil mix. This soil mix consists of approximately 20% stone washed aggregate (1” size, uniformly graded without fines, angular, not limestone) and 80% sandy, silty soil mix. Of this sandy silty soil mix, 85% should be top-soil, 10% is calcined diatomaceous earth for water retention, and 5% composted yard waste. This mix will allow the soils to be compacted to prevent settlement while providing continuous voids in which the roots can grow.

• Provide positive connection to storm sewer for run-off overflow.• In general Tree Trenches should not be located adjacent to steam lines. Insulation and

passive venting may be required, if trenches are too close. • Investigate utilities to determine feasibility of Tree Trench location.

Typical Tree Trench Details are shown in Figure 4-23.Proposed locations for tree Trenches on campus are shown in Figure 4-24.

Figure 4-23 TYPICAL TREE TRENCH DETAILSFigure 4-24 POTENTIAL TREE TRENCH LOCATIONS ON CAMPUS

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As BMPs, Rain Gardens and Tree Trenches are more efficient in removing NPS pollutants than the lawns they replace, in part because their deep rooted vegetation and amended growing medium allows water to filter through the soil. Related environmental benefits, such as atmospheric reduction of CO2, evapo-transpiration, habitat value and overall improvement of campus aesthetics are also important benefits.

With a Tree Trench the assumption is that runoff is captured from the surrounding area and conveyed into the trench. It is important to grade the area surrounding the trench to create positive drainage to capture stormwater. It is also important to connect surface drains to these trenches to provide a back-up in heavy storms and prevent flooding. The assumption of an additional capture of runoff from an equal amount of surrounding surface is a variable but should be included in the design of this BMP wherever possible, to enhance volume reduction. Sub-surface storage should also be included to infiltrate groundwater where aloowed by soil conditions and sub-surface utilities. Stormwater volume reductions are based on evapo-transpiration and infiltration. For cost estimating purposes a typical tree trench is assumed to be 15 ft by 8 ft by 2.5 ft deep. Volume storage capacity is assumed to be 36 cubic ft.

Table 4-11 Please note cost assumptions date from 2002.

COST ASSUMPTIONS FOR TREE TRENCHES*

Item $/SF

Soil Amendment $1.50 Stone $3.00 Vegetation $20.00 Piping $0.50

Total $25.00

4.4 NON STRUCTURAL BMPS

Several non-structural BMPs are suggested for the UNC-Chapel Hill campus to prevent pollutant incorporation in stormwater runoff.

PAVEMENT CLEANING

This BMP is a non-structural measure intended to remove pollutants from land surfaces that accumulate the most significant amount of NPS pollutants, (especially particulates) by maintenance measures such as street sweeping.

The University presently maintains over 121 acres of roads and parking areas that represent over 16 % of the campus Figure 4-25. The primary non-structural BMP of sweeping and vacuuming streets and parking lots can significantly contribute to the reduction of NPS pollutants entering the storm sewer system, although this measure offers no volume reduction benefit.

While street sweeping has been considered a good housekeeping technique for decades, earlier mechanical sweeper technology could not pick up fine-grained sediments that contained a substantial amount of the pollutant load. New equipment available today can collect particles less than 10 microns in diameter (a human hair is 40-120 microns in diameter.)

There are three basic types of sweepers, effective under wet, dry and frozen conditions:• Traditional mechanical sweeper that conveys the debris into a hopper for removal• Regenerative Air sweepers that blow air on the road surface, loosening fine particles and

sediments, which are then vacuumed up.• Vacuum Filter Sweepers that combine the mechanical process with a high powered

vacuum to capture small particles.

The optimal frequency for a street sweeping program varies with local weather patterns. Whenever possible ensure that areas with high amounts of debris be cleaned before a storm. While it is difficult to predict storms and clean accordingly, an alternative approach is to sweep bi-weekly and provide extra services to construction sites.

ILLICIT DISCHARGE ELIMINATION

In order to meet the requirements of the University’s Phase II NPDES Permit specific tasks have been identified in order to assist in the detection and elimination of illicit discharges to stormwater. An important part of this program is the on-going mapping of the University’s stormwater piping system. The expected completion date for this mapping is 2006.

PUBLIC EDUCATION AND OUTREACH

There are a number of public education and outreach programs already in-place in the UNC-Chapel Hill Department of Environment, heath and safety. Further stormwater educational programs and materials for students, faculty and staff are being developed to increase their awareness of how campus activities can impact water quality.

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Figure 4-25 POTENTIAL PAVEMENT AREAS FOR PAVEMENT CLEANING PROGRAM

INTEGRATED PEST MANAGEMENT PROGRAMS AND SALT AND FERTILIZER REDUCTION

Fertilizer

“There are significant economic costs associated with the inefficient use of fertilizer, and by the damage caused to aquatic, terrestrial, and marine ecosystems, to the ozone layer and through the climate change by the introduction of reactive nitrogen... (and) only one quarter to one third of applied fertilizer nitrogen is actually absorbed by crops.”

William Moomaw, Tufts University, American Association for the Advancement of Science (AAAS) Meeting February 17, 2003.

Reduction of fertilizer application on maintained landscapes especially Lawns, Athletic Fields and Intermural Fields is an important measure to reduce water quality impacts. The goal is to adopt fertilizer application rates that will maximize the appearance and quality of the campus but also minimize pollutant load.

Soil samples should be taken to determine missing plant nutrient requirements before a fertilization program is carried out. Testing should be done with every new planting and again one or two years after the installation of new landscapes and every 2-3 years for established landscapes. Based on these soil samples, fertilizer timing and rate can be adjusted so that nutrients are not applied in excess ending up in the groundwater and streams.

Fertilizing is neither necessary nor desirable in all areas of the campus. Fertilizer often benefits weed species. In contrast, many native species are adapted to the range of soil and pH conditions that exist. The use of organic fertilizer and compost should also be considered, especially when creating new planting beds. Compost improves structure, water-holding capacity and nutrient content of the soil.

SaltReducing road salt (calcium chloride) can also reduce pollutant loads. A study monitored five different infiltration basins for water quality and analyzed the runoff entering and the groundwater below each basin for arsenic, cadmium, calcium, carbon chloride, chromium, lead, magnesium, nitrogen, phosphorous, potassium, sodium and sulfate. “Concentrations of most constituents were low, generally within the standards for potable water. A major exception was road de-icing salts in the winter.” (Ku, H. F. H. and Simmons, D. L., 1986, Effect of Urban Stormwater Runoff on Ground Water Beneath Recharge Basins on Long Island, New York: U. S. Geological Survey Water-Resources Investigations Report 85-4088, 67p.) The Vermont Agency of Transportation has been able to reduce the statewide use of salt by 28% by mounting infrared sensors on truck beds to determine if the road temperature, which is often warmer than the air temperature, actually warrants a salt application.

The following guidelines for fertilizer timing and application are summarized from information published by the North Carolina Cooperative Extension Service.

Areas for Pavement Cleaning

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Table 4-11.

FERTILIZER APPPLICATION RATES

DECIDUOUS SHADE TREES Ratio: 10-5-5, 12-6-6, 18-6-12 Time; October – March Rate: 1 – 2 Lbs actual Nitrogen/1000 Square Feet

SMALL TREES AND SHRUBS Ratio: 16-4-8, 12-4-8 Time; Late Fall Rate: 2-4 lbs of complete fertilizer per 1000 Square Feet/Year

AZALEAS AND RHODODENDRONS Ratio: 8-8-8, 10-10-10 Time; Split applications March, May, July Rate: 2-3 pints/ 100 Square Feet

ATHLETIC FIELDS Ratio: 12-4-8, 16-4-8, 8-8-8, 10-10-10, 95-0-0-, 33-0-0 Time; September and November Rate: 1 Lb. actual nitrogen per 1000 Square Feet/ 2X a Year

LAWN Ratio: 12-4-8, 16-4-8 Time; February, September and November Rate: Slopes and Sandy Soils .25-.50 Lb. Nitrogen per 1000 Square Feet/ Year

1 Lb. actual nitrogen per 1000 Square Feet/ 2X a Year

NON-STRUCTURAL BMPS TO SLOW RUNOFF RATES, REDUCE VOLUME AND ABSORB POLLUTANTS

Land Cover ConversionsIn an integrated stormwater management plan, the landscape is an important factor not only in sustaining the aesthetic and functional resources of the campus, but also in mitigating the amount and rate of stormwater runoff.

The UNC-Chapel Hill campus needs to be both coherent and attractive. Its rich natural and cultural heritage makes it a special place, with the steep forested slopes providing the setting for campus life. On the main campus the major landscapes include:

(1) the flat, open, greens of the historical core, with their huge relic forest trees, in the northern part of the main campus and:

2) the forested slopes, the streams and their narrow floodplains in the southern part of main campus.

It is these elements of the campus landscape that are remembered and treasured, by both students and alumnae. The land conversion strategies recommended in this plan strengthen the inherent character of the campus.

Land cover conversion allows the University to replace non-essential lawn areas with vegetation that reduces both the rate of surface runoff and the associated pollutant load, (Figure 4-26). Some volume reduction is also possible, since precipitation is held on the land longer and allowed to evaporate and soak in to the more absorbent surface layer. A significant portion of the campus is potentially suitable for this BMP as shown in Figures 4-27, 4-28, 4-29 and 4-30.

Figure 4-26 STEEP SLOPES WITH UNNECESSARY LAWN AT FAMILY MEDICINE BUILDING

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Figure 4-27 POTENTIAL LAND COVER CONVERSIONS IN SUB-WATERSHEDS ME-1, ME-2, ME-4, BO-1,AND BO-2

KenanStadium

UNCHospitals

BellTower

McCorklePlace

KenanStadium

CarmichaelField

DavisLibrary

Ehringhaus

Figure 4-28 POTENTIAL LAND COVER CONVERSIONS IN SUB-WATERSHEDS ME-3, ME-4, ME-9, AND CH-1

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Figure 4-29 POTENTIAL LAND COVER CONVERSIONS IN SUB-WATERSHED ME-2. Figure 4-30 POTENTIAL LAND COVER CONVERSIONS IN SUB-WATERSHEDS ME-4, ME-5, ME-6 AND ME-9

AmbulatoryCare Center

Cardinal &Dogwood

Parking Decks

OdumVillage

BaityHill

Dean E. SmithStudent Activities

Center

CraigeParking

Deck HintonJames

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Table 4-12

ACREAGE OF PROPOSED LAND COVER CONVERSIONS

• Restore Managed Woodland to Forest 16.42 Acres • Convert Lawn to Planted Areas

(Groundcover/Low Shrubs/Grasses) 23.42 Acres • Convert Lawn to Old Field Meadow 6.32 Acres • Convert Rough Grass to Old Field Meadow 1.87 Acres • Convert Rough Grass to Planted Areas 1.61 Acres • Impervious Surface to Planted Area 9.84 Acres • Impervious Surface to Old Field Meadow 0.42 Acres

This study considers a number of changes to the campus landscape that will produce less runoff and require little if any application of chemicals. These measures include lawn or rough grass conversions to meadow, old field, horticultural plantings or rain gardens, rough grass conversions, and forest restoration. Increasing the roughness and variation of the surface will lower the Curve Number and therefore decrease the net amount of immediate runoff. Reducing the Curve Number in the WBM allows a higher estimate of the amount of rainfall that soaks into the soil and does not contribute to immediate runoff. Actual reduction in runoff volume varies with the type of vegetation conversion, but this BMP can hold as much as 0.5 inches of rain during a 2-year storm. On an annual basis, the amount of evapo-transpiration from these landscape conversions should increase by several inches.

Recommendations for Campus Land Cover Conversions

• Reduce lawn and whenever possible, confine to flatter areas.

Reducing the extent of lawn is one of the easiest and most effective ways of improving water quality. Lawns on gentle slopes can shed water nearly as rapidly as pavement. In contrast to lawn, “natural forest soils with similar overall slopes can store up to 50 times more precipitation than neatly graded turf.” (Arendt, Randall. Growing Greener, Putting Conservation into Local Plans and Ordinances)

Existing lawn areas can be converted to a number of different land cover types that include:1. Horticultural Plantings- Groundcover/Low Shrubs/Grasses2. Meadow, Old Field and Savannah3. Rain Gardens

While turf is inexpensive to install, the cost of maintenance to promote an attractive healthy lawn is high—requiring mowing, irrigation, fertilizer, lime and herbicides—all have a negative impact on water quality.

Comparison of land cover types in existing conditions with those of the Eight-Year Development Plan indicates that proposed areas of lawn will increase by some thirty plus acres. and areas of forest will decrease by some twenty-seven acres.

• Gradually convert lawn on slopes over 6%

Replace lawn on slopes with densely planted, more complex cover types including, wildflowers, ferns, grasses and seedling size trees and shrubs, leaving little exposed soil or mulch. Favor native plant species on slopes and at the edges of the campus, as these species are adapted to the local climate and are deep rooted allowing them to tolerate drought (Figure 4-31).

Figure 4-31 EXAMPLE OF LAWN CONVERTED TO PLANTED AREAS AT THE FRONT OF WILSON HALL, CONCEPT PLAN AND SECTIONS

• Increase forested areas by restoring managed woodland to forest:

There are 24.48 acres of cleared woodland on the existing campus plan.The most straightforward way to restore natural hydrologic patterns is to reforest all steep slopes on campus. Where these slopes are already in cleared woodland this means converting managed woodland back to layered forest. This forest should be a native plant community managed and selectively thinned to provide greater visibility, while retaining the natural stratification of canopy, understory, shrub and ground layers. At UNC-CH managed woodlands are typically found at the edges of developed areas. The proposed construction over the next eight years will decrease the acreage of managed woodland on the campus by 6.3 acres, leaving more than 17 acres for forest restoration. The restoration of these remaining woodland areas will benefit from a systematic, long-term management program in which small scale projects are initiated and include monitoring the landscape, stabilizing erosion, controlling exotic species and developing specific approaches for difficult conditions on campus (Figure 4-32).

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Figure 4-32 EXAMPLE OF MANAGED WOODLAND CONVERTED TO FOREST AT THE DEAN E. SMITH CENTER, CONCEPT PLAN AND SECTIONS

• Convert rough grass areas to more complex cover types:

Rough grass is poorly maintained lawn frequently with a high percentage of bare spots and weed species. Where rough grass occurs within the campus, these areas can be replanted to meadow or more complex core types. As the campus develops, areas that have been construction-staging sites and transition areas that require stabilization for erosion control may also be good candidates for this planting strategy. At present, there are over four acres of rough grass on the campus that could be restored to other land cover types.

Rough grass conditions occur primarily on the campus along woodland edges. They tend to be linear configurations, following roadways and paths. It is common to find areas of rough grass that extend right up to the edge of a steep wooded hillside on both north and south facing slopes. By maintaining a simple buffer of native meadow grasses, perennials and woody pioneer species, it is possible to reduce run-off and in turn reduce erosion and sedimentation.Tall grass cover is especially suitable for sites where a dense, stable cover must be established fairly quickly. Tall grass meadow is composed primarily of native grasses with occasional naturalized alien grasses and wildflowers. (Figure 4-33). Eventually this cover type will return to forest if it is not mowed or burned bi-annually. Almost any site with 40% or less tree cover can be stabilized with native grasses. The acid, infertile subsoil, which occurs on disturbed sites is a poor medium for turf, but will support a dense growth of native grasses with only minimal maintenance required (Figure 4-34).

Figure 4-33 EXAMPLE OF A WILDFLOWER MEADOW BORDER AS A BUFFER BETWEEN LAWN AND FOREST

Figure 4-34 PLAN SHOWING ROUGH GRASS CONVERTED TO MEADOW AT THE BACK OF EHRINGHAUS DORMITORY,

IrrigationDrip irrigation is required for all plant establishment during the first growing season, at a minimum. Irrigation is not recommended on an ongoing basis for meadow and woodland plantings, though it will be necessary in planting beds.

DecompactionSoils that are compacted by construction staging will require decompaction and soil amendments to restore fertility and soil structure. Cost estimates should assume that all soils are loosened at least to a to a depth of 12”.

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4.4 COMPARISON OF BMP EFFICIENCIES

Volume Reduction Benefit

Because the link with the GIS spatial file requires that these BMP benefits be described in volume per unit area, as cubic feet per square foot (CF/SF) of BMP, volume reduction values for the various BMPs discussed are summarized in Table 4-13, in inches per square foot of BMP and are recast in Table 4-14 in cubic feet per square foot.

If ordinance compliance for volume is the only concern, measures that are easiest to build and cost the least should be chosen. This is a reasonable first step for the Stormwater Management Plan and Tables 4-13 and 4-14 show that structural BMPs provide greater volume reduction on a square foot basis. However in some cases the opportunities to build these BMPs are limited and there is a greater opportunity to build measures such as Rain Gardens, Tree Trenches and to Convert Lawn to other cover types. These BMPs while less efficient on a square foot basis nonetheless can have a significant cumulative effect and also offer substantial pollution reduction benefits.

Table 4-13

VOLUME REDUCTION BENEFIT FOR SELECTED BMPs (Inches per square foot of BMP)1” rainfall 3.6” rainfall 46” annual

Pemeable Pavement 2” 7.2” 44” with Storage/Infitration Beds

Other Surfaces 2” 7.2” 44” With Storage/Infiltration Beds Vegetated Roof 1” 1.7” 32”

Roof Gardens 2” 2.8” 41”

Runoff Capture and Re-use 1” 3.6” 46”

Rain Gardens 0.2” 0.57” 3”

Tree Trenches 0.9” 3.6” 6”

Lawn Conversions 0.2” 0.2 – 0.5” 3”

Table 4-14

VOLUME REDUCTION BENEFIT PER BMP MEASURE (Shown in Cubic Feet per Square Foot of BMP)

1” rainfall 3.6” rainfall 46” annual

Permeable Pavement 0.17 0.60 3.67 with Storage/Infitration Beds

Other Surfaces 0.17 0.60 3.67 With Storage/Infiltration Beds

Vegetated Roofs 0.08 0.14 2.67

Roof Gardens 0.17 0.23 3.42

Runoff capture and Re-use 0.08 0.15 to 0.33 3.83

Rain Gardens 0.02 0.05 0.25

Tree Trenches 0.07 0.30 0.50

Lawn Conversions 0.02 0.02 to 0.04 0.25

Permeable Pavement with Infiltration/Storage Beds

With permeable pavement the pavement surface is capable of infiltrating the total amount of rain during any given storm, the storage capacity of the bed can hold this volume, if the soil is capable of infiltrating the stored volume so that the bed is drained before the next rainfall, and if runoff from a contiguous area of equal size can be conveyed to the bed, effectively capturing twice the rainfall. During a rainfall of 3.6 inches in 24 hours, this BMP is assumed to hold 7.2 inches of volume per unit area. This volume reduction applies to all types of storms, up to the 100-year frequency rainfall. It should be stressed that the limiting factor is the ability of the bed to infiltrate the runoff into the sub-soil in a reasonable time period following rainfall.

Other Surfaces with Storage/Infiltration Beds

This BMP offers the potential for substantial volume reduction because of the location of possible bed sites and the extensive surface areas possible. Again, the limiting factor is the ability of the bed to infiltrate the runoff into the sub-soil in a reasonable time period following rainfall. These areas may also collect and capture runoff from upstream and adjacent lands, but in the lower lying play field locations, infiltration may be constrained by the water table near the surface. A volume reduction of 7.2 inches is assumed during the 2-year rainfall, but should be reevaluated with every site design. In some situations, these beds provide a kind of reverse flood plain storage, with the volume of runoff held in a stone bed rather than a riparian flood plain, now filled with earth and structure. This is a less desirable alternative than the preservation of the natural riparian system.

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Runoff Capture and Re-use

The potential capture for this BMP varies, and for some situations could result in a “zero runoff” condition under any rainfall. However, it is impossible to assign an average capture number, as in the case of the storage beds and rain gardens. The 2-year value applied is 3.6 inches, since in most of the anticipated applications the contributing surface area will be limited to direct rainfall on the BMP.

Vegetated Roof Systems

The volume removed by this BMP varies with the design. On average, a simple vegetated roof reduces annual runoff by 70%. It can retain the entire initial 1-inch of runoff, and is assumed here to reduce the 2-year frequency design storm (3.6”) by 1.7” during a heavy rain. The detention capacity of this BMP is greater than the 1-inch rainfall and effectively reduces the peak rate of discharge by 2.5 inches or more. Roof garden systems are substantially different in form and function, with the possibility of an additional 20” of water added per unit area by irrigation to the natural 46” rainfall. However, this type of design can also collect rainfall from adjacent roof areas and hold it in cisterns for subsequent re-use as irrigation. The volume “credit” applied in such a system is actually increased, with the assumption that 2.8” is removed per unit area during the 2-year rainfall, because of this storage capacity.

Rain Gardens

For this BMP, improved soil retention and subsequent uptake of rainfall by the vegetation provides volume reduction. A volume reduction of 0.5” during the 2-year storm of 3.6” is assumed. Additional storage capacity is possible under optimal conditions with the use of a sub-surface storage and infiltration bed. If storage and infiltration capacity are included, volume reduction efficiency could be 2 inches or more for the 2-year rainfall.

Tree Trenches

With Tree Trenches designed as suggested, runoff should flow into the trench from the surrounding land, so that an equivalent volume reduction of 1.8 inches from twice the area during the 3.6-inch rainfall, for a total of 3.6” can be assumed. However capture of additional runoff from an equal amount of surrounding surface is a variable. Inclusion of sub-surface storage that subsequently infiltrates to groundwater will increase the effectiveness of this BMP. Estimated volume reduction of this measure will vary across the campus, due to variation in soil and the location of sub-surface utilities.

Cost Comparisons

Although the structural BMP measures discussed are quite different in form and application, it is useful to compare them on the basis of the unit cost of runoff volume reduction, operation and maintenance costs as well as total construction costs. Feasibility and applicability issues, are considered in Chapter 5. On a first cost basis, Table 4-15 shows BMP measures in terms of estimated cost per unit area (square feet), as measured in the GIS program.

Some measures such as water quality inlets, do not lend themselves to this scale and so an assumption is made as to the number of units to be installed per acre of maintained landscape (10) at a fixed cost ($1,000 each, installed), for a unit cost of approximately $0.22 per square foot. Depending on the configuration and location of inlets in the existing storm drain system, this unit cost could vary widely, but for comparison purposes a representative figure is given. For landscape BMP, such as rain gardens and lawn conversion to several different cover conditions, the analysis is supported by detailed concept designs and cost estimates, in Appendix E.

Table 4-15

UNIT COSTS OF SELECTED BMPs

Measure Unit Cost O&M Cost ($/SF) ($/SF/yr)

Permeable Pavement 8.00 0.04 with Storage/Infitration Beds

Other Surfaces with Storage/infiltration 7.00 0.02

Vegetated Roofs 21.00 0.03

Water Quality Inlets 0.22 0.11

Runoff capture and re-use 21.00 0.05

Rain gardens 10.00 0.25

Tree trenches 21.00 0.40

Lawn conversion 5.00 0.20

Forest restoration 5.00 N/A

The wide range of unit costs suggests that if all of the measures listed were equally feasible and there were equal opportunities for these BMPs to be applied throughout the campus, it would be appropriate to simply choose the least expensive BMPs to achieve volume reduction. The potential application sites within the campus shown in Chapter 5 show that on many sites, use of all BMPs equally is not possible. For example, while the landscape measures are widely distributed and potentially successful, at least in terms of meeting the Town volume criteria, they are substantially more expensive than the larger, single site structural measures, such as storage/infiltration beds. However, opportunities for installation of these structural measures are limited, and in some cases are conditional on the success of the initial demonstration efforts.

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One way of optimizing the BMP selection process is to apply a Cost-Benefit Analysis. Table 4-16 defines “the benefit” as the potential volume reduction.

Table 4-16

COST BENEFIT ANALYSIS OF VOLUME REDUCTION BY SELECTED BMPs

Measure Unit Cost Volume Reduction Cost Benefit 2-year rainfall ($/SF) (CF/SF) ($/CF)

Permeable Pavement 8.00 0.60 $13 With Storage/Infiltration

Other Surfaces Storage/infiltration 7.00 0.60 $12

Vegetated Roof System 15.00 0.14 $107

Roof Garden 21.00 0.23 $91

Runoff Capture and Re-use 21.00 0.15-0.33 $63 - $140

Rain gardens 10.00 0.05 $200

Tree trenches 21.00 0.30 $70 Lawn conversion 5.00 0.02 - 0.04 $125 — $250

Figure 4-35 illustrates the Costs and Benefits in graphic form, and makes clear that the greatest volume reduction is achieved by the largest structural measures. This reflects an economy of scale not achievable by more widely distributed measures, with infiltration beds offering the greatest total volume, some 48% of the possible storage, within the two phases of anticipated implementation. Pervious Pavement with storage/ infiltration offering 15% of the possible storage, Roof Gardens 11% and Runoff Re-use 6%. Although these BMPs are site specific, these figures suggest that there should be further evaluation of the use and application of each structural measure.

Figure 4-35 COST BENEFIT ANALYSIS OF VOLUME REDUCTION BY SELECTED BMPS

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4.5 WATER QUALITY BENEFITS

INTRODUCTION

In most situations, reduction of runoff volume also reduces the mass transport of pollutants, especially where stormwater passes through an infiltration system. Avoidance, transport reduction, elimination, capture, or a combination of all these, are all strategies to improve water quality.

When combined with a program to reduce fertilizers and to increase pollutant removal, significant volume reduction and NPS reduction is possible. Some of the BMPs recommended, especially the non-structural measures, reduce surface runoff. This can be done in a number of ways; by creating a rougher and denser vegetative cover, by providing a permeable surface that filters pollutants, or by catching and removing pollutants as they move through the storm sewers. Once NPS pollutants are suspended or dissolved in runoff their removal is far more difficult. Intervention in the runoff flow is the most difficult option for water quality, although a number of new methods and techniques have been developed over the past ten years. Pollutant capture by measures that slow, filter, separate, settle, skim or in some fashion treat stormwater in transit, has dominated the shopping list of “innovative BMPs” in many recent publications on stormwater management (ASCE, 2002).

However, evaluating the net benefits of pollutant reduction is more complex than the issue of volume reduction. In order to define the potential benefit of any given measure, the water quality problem must be understood in the context of how much pollution is conveyed during runoff from the campus under current conditions. The Water Balance Model (WBM) analysis with the detailed summary tables (Appendix B), estimates the “event mean concentration” of each pollutant anticipated in the stormwater runoff. These values were applied in the WBM to predict the pollutant load scoured from various landscape surfaces with each rainfall, using the 1-inch, 3.6-inch and annual (46 inches) total to develop the mass loading estimates with the WBM, as illustrated in that section.

Where landscape cover change is proposed, the reduction in immediate runoff is estimated by a change in the “curve number” in the hydrologic model. The actual removal of pollutants from the new or constructed surfaces is added to this benefit. These changes in curve number are used in the WBM to analyze the Eight Year Development Plan.

For comparison purposes, the changes in land use applied in the three WBM runs are summarized in Appendix B. As might be expected, land use impacts the quality of the runoff. Roads generate more suspended solids than rooftops, and natural woodlands produce less runoff and less nitrogen than maintained landscapes. The relatively small increase in total impervious surfaces resulting from the Eight-Year Development Plan amounts to only 6.5 acres. Most of the net change in impervious cover represents an overall reduction in roadways and parking lots (21.3-acre reduction) and a replacement with relatively clean rooftops (25-acre increase).

The various pollutants considered in the model are conveyed with the runoff in both particulate form and as solutes. Table 4-17 shows the estimated pollutant load generated on an annual basis that can be expected after the build-out of the Eight-Year Development Plan. While the

current pollutant load generated from the campus is reduced, it will be difficult to make much of a dent in the total load without application of the various BMPs proposed. This pollutant load is derived only from stormwater transport. Dry weather transport which is relatively small for most pollutants is not included.

Table 4-17

STORMWATER POLLUTANT ANNUAL TRANSPORT (tons/year)

Existing Eight-Year

Suspended Solids 148.5 128.4 Nitrogen (as Nitrate) 1.35 1.25 Total Phosphorus 0.9 0.8 Chemical Oxygen Demand 96.7 85.9 Oil & Grease 5.9 5.1 Metals (Pb, Zn, Cu) 0.3 0.3

In Meeting of the Waters, the watershed undergoing the greatest change with 3.8 net additional impervious acres, the current suspended solids load will be reduced from 99.8 tons/year to 81.8 tons/year on an annual basis, as many of the new structures will cover existing pavement and parking surfaces, reducing the suspended solids pollutant load per unit area from 135 mg/l to 1 mg/l during rainfall.

Pollutant reduction occurs because dirtier surfaces are replaced with cleaner surfaces in the Eight-Year Development Plan. Taking this conclusion to the extreme, if the campus were completely covered with buildings, less pollution would be generated. While this may be true, the resulting volume of runoff would increase and continue to erode downstream channels, generating additional sediment. All pollutant reduction resulting from the Eight-Year Development Plan, while minor in scale, is independent of any additional BMP construction.

SUSPENDED SOLIDS (SS)

As illustrated in the previous section, different land surfaces on the campus produce particulate pollutants in various amounts, and the average concentration in stormwater runoff varies by land cover and use. The Water Balance Model compared the relative loading or mass transport under existing conditions and under the Eight-Year Development Plan. Smaller rainfalls generate a smaller load of Suspended Solids.

On an annual basis, the net change is shown in Table 4-18 and Table 4-19. The lower figures in Table 4-18 reflect the fact that most surfaces generate little runoff or suspended solids until the rainfall approaches 1 inch. The relative efficiencies of each BMP type is shown in Table 4-20. Construction of the proposed BMPs produces a slight increase in Suspended Solids for the total year in Meeting of the Waters Creek, showing that these measures are less effective in reducing pollutants during larger storms, when rainfall overflows these BMPs or exceeds their infiltration and storage capacity.

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Table 4-18

SUSPENDED SOLIDS LOADING DURING THE INITIAL 1-INCH RAINFALL(Pounds/Year)

Watershed Existing Eight-year With Potential BMPs only

Battle 384 383 382

Bolin 175 147 147

Chapel 155 155 155

Meeting of the 2152 1932 1894 Waters Morgan 263 258 250

Table 4-19

SUSPENDED SOLIDS LOADING TOTAL ANNUAL RAINFALL (PoundsYear)

Watershed Existing Eight-year With Potential Development BMPs only

Battle 38,985 38,828 38,656

Bolin 17,212 14,784 14,707

Chapel 17,244 17,241 17,208

Meeting of the 199,668 163,498 177,375 Waters

Morgan 23,888 22,397 22,272

TOTAL 296,997 256,748 270,218

Table 4-20

ANNUAL SUSPENDED SOLIDS REDUCTION BY STRUCTURAL BMP MEASURES

Measure Percent Reduction

Pervious Pavement 95%

Vegetated Roof (simple) 90%

Water Quality Inlets 30-60%

Lawn Conversion 50%

Rain Gardens 60%

Tree Trenches 60%

Storage/infiltration 80%

Runoff Capture and Re-use 100%

Table 4-21

COMPARISON OF BMP EFFICIENCY FOR SUSPENDED SOLIDS

CATEGORY 1. MAJOR VOLUME SYSTEMS 3,221 pounds CATEGORY 2. OTHER STRUCTURAL SYSTEMS 134 pounds

CATEGORY 3. LANDSCAPE MEASURES 323 pounds

The impact of these pollutants on the receiving streams remains the most important issue. In the major campus watershed, Meeting of the Waters, annual transport of almost 100 tons of sediment has a very negative downstream impact. Reduction to 80 tons a year under the eight year development is a step in the right direction, but will not improve overall water quality improvement downstream. In answer to the question of how much this pollutant can be reduced in runoff, a simple but effective answer is “as much as can be reasonably accomplished within the capabilities of available technologies”. This is a “Best Available Technology” (BAT) approach to NPS pollution and makes great sense for the larger Cape Fear River Basin.

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Are the proposed BMP measures justified in terms of improving water quality in campus watersheds? The first question to evaluate is the location of the proposed BMPs in the respective drainage systems—will they do the most good on the parcels where they are feasible to install? Meeting of the Waters watershed is a composite of eight rather different sub-watersheds totaling 441 acres of highly developed land, generating 19,722 pounds (or 10 tons) of Suspended Solids in the runoff during a two-year storm. This pollutant load is produced from a mix of land surfaces, with pavements and lawns producing 88% of the load, and play fields responsible for only 4% (Figure 4-36).

Figure 4-36 TOTAL SUSPENDED SOLIDS LOAD FOR 2 YEAR RAINFALL ME WATERSHED

This load can be reduced by the BMPs considered, with the infiltration beds potentially most successful and least expensive, but they must be used in the areas responsible for pollutant generation. Unlike the reduction in runoff volume, the generation of pollution is surface specific—the levels of pollutant reduction possible depend on changing the actual surfaces generating the pollutant.

In the case of the Athletic and Intramural Fields, with storage and infiltration beds beneath, the rainfall will infiltrate into a stone layer and subsequently into the soil. In some cases, this runoff may be captured and returned to the field as irrigation. Any nutrients applied will be re-used. For Carmichael Field, the adjacent athletic field is underlain by an impervious surface, and this runoff will also be captured, at least in part, and re-used. Because most of the fields in sub-watershed ME-3 were built over the small streams when the land was filled, the drainage passing through these pipes comes from upland impervious surfaces, including rooftops and roadways. If this runoff can be included in the capture/irrigation system, runoff produced will be virtually free of suspended solids downstream. The annual load of 148.5 tons will be reduced to 128.4 tons with build out of the Eight-Year Development Plan, and if the various structural BMPs are built, total load will be reduced to 106.5 tons (Table 4-22).

Table 4-22

REDUCTION OF SUSPENDED SOLIDS BY BMPs

EXISTING SUSPENDED SOLIDS LOAD 148.5 TONS PER YEAR

8-YEAR SUSPENDED SOLIDS LOAD 128.4 TONS PER YEAR

POTENTIAL LOAD REDUCTION BY BMPS 21.9 TONS PER YEAR

TOTAL LOAD AFTER BMPs 106.5 TONS PER YEAR

The present campus maintenance programs of street vacuuming will do more to reduce this suspended solids load than more expensive structural measures. Installation of small inlets with containers that are periodically cleaned are also very effective, especially in those portions of the campus where no other BMPs are suitable. Table 4-23 compares the benefit of these non-structural measures with structural BMPs.

Table 4-23

COMPARISON OF POTENTIAL SS LOAD REDUCTION (CAPITAL COST ONLY)

MEASURE LOAD TOTAL COST REDUCTION COST BENEFIT (TONS/YEAR) (M$) ($/TON)

BMP LOAD REDUCTION 21.9 35.4 $1,616,438

STREET VACUUMING (121 ACRES) 30 0.5 $16,667

WATER QUALITY INLETS (100 AT 140#/YR) 7 0.1 $14,285

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Nitrogen as Nitrates (No3N)

The same list of potential BMPs was used to evaluate the potential reduction of soluble Nitrate. Since dissolved pollutants are conveyed in runoff in a relatively constant concentration volume reduction is important as more runoff means more pollutants. Table 4-24 summarizes the Nitrate removal assumed for each BMP.

Table 4-24.

NITRATE REDUCTION IN STORMWATER BY BMP

BMP % REDUCTION

PERVIOUS PAVEMENT 20

VEGETATED ROOF 60

ROOF GARDEN 60

WATER QUALITY INLETS 40

LAWN CONVERSION 80

RAIN GARDEN 80

TREE TRENCH 80

INFILTRATION BEDS 20

CAPTURE AND RE-USE 100

STREET VACUUM UNITS 30

FERTILIZER REDUCTION 30 to 90

The total campus produces a Nitrate load of 148 pounds in the 2-year rainfall, 100 pounds from Meeting of the Waters watershed alone. Figure 4-37 shows that lawn is responsible for 30% of this load, with roads and parking accounting for 29%, pathways for 13% and buildings for 17%. Athletic Fields and Playfields only account for 6%.

Figure 4-37 NITRATE LOAD FOR 2-YEAR RAINFALL IN ME WATERSHED

Each BMP has a very different efficiency of Nitrate reduction. The 4.58-pound reduction with initial projects is accomplished largely by the Athletic Fields, providing 66% of the mitigation, with rain gardens and tree trenches together providing 23% (Figure 4-38). While the efficiency of the various measures is a consideration, overall reduction is relatively small (6.7%) in terms of the total load generated by the ME watershed—less than ten pounds from a transport load of 148 pounds.

Table 4-25 compares the total annual nitrate load under existing conditions and under the Eight-Year Development Plan, with the amount of nitrates reduced by various BMPs. This table illustrates that for nitrate reduction non-structural measures have the greatest potential to improve water quality. Although, fertilizer reduction programs currently in place at UNC-Chapel Hill for both Lawns and Athletic Fields can not be estimated until further data is collected and analyzed, the University Grounds Department is reducing fertilizer, salt and pesticide/herbicide application wherever possible, and exploring ways to reduce their use still further. It is important to note that reduction of nitrates by as much as 30% or 543 pounds/year, could be achieved by cover conversions and street sweeping alone.

Table 4-25.

ANNUAL NITRATE LOAD REDUCTION (#/yr)—MTG. OF WATERS

TOTAL EXISTING ANNUAL NITRATE LOAD 1,811 POUNDS

TOTAL ANNUAL NITRATE LOAD 1,648 POUNDSEIGHT-YEAR DEV. PLAN

REDUCTION WITH BMPs, 104 POUNDS

REDUCTION WITH STREET VACUUM 170 POUNDS

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Table 4-26

TOTAL PHOSPHORUS REDUCTION IN STORMWATER BY BMP (% REDUCTION)

BMP % REDUCTION


VEGETATED ROOF 90

ROOF GARDEN 80

WATER QUALITY INLETS 50

LAWN CONVERSION 60

RAIN GARDEN 60

TREE TRENCH 60


CAPTURE AND RE-USE 100



CHEMICAL OXYGEN DEMAND (COD)

The final NPS pollutant considered in this report is Chemical Oxygen Demand, a collective measure of the organic matter present in runoff. This organic matter includes all of the natural detritus flushed into a stream, such as leaves and decaying vegetation, to the human detritus scoured from our community, including paper, animal waste, discarded material of all types, grass clippings, petroleum drippings, lawn chemicals and anything that winds up in our gutters and inlet boxes. This load of waste materials subsequently decays in waterways, exerting a demand for oxygen that significantly impacts micro and macro-organisms that sustain water quality, including finfish communities. The available scientific data indicates that this load is equal to or greater than that discharged from wastewater treatment plants as residual effluent, and is therefore an important part of the NPS load reduction program for the campus. The potential efficiency of the BMPs for COD reduction is shown in Table 4-28 and in Figure 4-40 and 4-41.

Figure 4-38 NITRATE REDUCTION BY BMP TYPE/2 YEAR RAINFALL/ME WATERSHED

Total Phosphorus (TP)

Transport of Phosphorus is closely related to transport of Suspended Sediment, and the reductions anticipated are proportional. Table 4-26 summarizes BMP efficiency assumed for TP reduction with the mix of BMPs measures considered. This table shows that BMPs can make a major impact on this nutrient, with a possible reduction of 71 pounds in a total of 215 pounds, or 33%. However, because Phosphorus is the likely cause of eutrophication in Lake Jordan, the desired reduction is actually on the order of 90% (given the background levels measured in Meeting of the Waters Creek). Again, insufficient data is available on stream water quality and TP transport throughout the watershed to reach final conclusions about the necessary load reduction for this pollutant at the UNC-Chapel campus.

Figure 4-39 PHOSPHORUS LOAD FOR 2-YEAR RAINFALL IN ME WATERSHED

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Table 4-28

TOTAL COD REDUCTION BY BMP MEASURES (% REDUCTION)

BMP PERCENT REDUCTION


RUNOFF CAPTURE AND RE-USE 100


VEGETATED ROOF 90


ROOF GARDEN 80

RAIN GARDEN 50

TREE TRENCH 50


LAWN CONVERSION 40

Figure 4-40 COD LOAD FOR 2-YEAR RAINFALL IN ME WATERSHED

Figure 4-41 COD REDUCTION BY BMP TYPE FOR 2-YEAR RAINFALL IN ME WATERSHED

WATER QUALITY BENEFITS BY BMP

The following section describes the water quality benefits of each BMP in terms of four major NPS pollutants—Suspended Solids, Nitrogen as Nitrates, Total Phosphorus and Chemical Oxygen Demand (COD)

Permeable Pavement and Other Surfaces with Recharge/Infiltration Beds Beneath

This system is very efficient in removing particulates, but allows solutes such as Nitrogen as Nitrates to pass directly through the pavement or vegetation and into the groundwater, creating a polluted base flow that contributes to the net flux of nitrates from the watershed. For organic pollutants, the soil provides a variety of treatment and removal processes both biochemical and physical. Nitrates are assumed to pass through the sub-surface without transformation by anaerobic bacteria.

Reduction or removal per unit area varies by pollutant. The removal mechanisms for particulate-associated NPS pollutants, such as metals, phosphorus, organics and some nitrogen forms, are a function of the cat-ion exchange capacity (CEC) of the soil. For the soils found in the Chapel Hill area, the removal efficiency is excellent. The same slow permeability that limits the application of infiltration measures also is very efficient in removing pollutants from the percolating rainfall, with the clay soils acting as a water quality filter.

When an infiltration BMP is used in an Athletic Field rehabilitation, care must be taken to minimize the application of fertilizers, especially Nitrogen. Some designs may lend themselves to subsequent capture and re-use of rainfall for irrigation, and some designs may actually include irrigation systems, but where these are installed every effort should be made to apply only captured rainfall.

(13,695 lbs. total)

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Vegetated Roof Systems and Roof Gardens

A simple green roof system, requires few additional nutrients or water in the North Carolina climate, and generates very little detritus or solutes in the small amount of rainfall that finds its way through the system and down to the surface. With a 70% retention rate of annual rainfall, the 30% that becomes surface runoff transports very little NPS pollution, and can be considered quite clean. Overall pollutant removal capability of a Roof Garden is also significant, but cannot equal a simple green roof system, since both nutrients and water are added (although there is the possibility of significant capture and use of precipitation).

Water Quality Inlets

The pollutant removal capability of this BMP varies greatly. Surface inlets collect runoff from relatively small areas and connect to larger pipes, These in turn may have additional inlets. The small European catchment “buckets”, cleaned on a regular basis, can do a very efficient job of collecting detritus and human trash. In Polk Place, some 40 small inlets are presently in place on the lawn and walks, connected to 5 larger inlet boxes. Each type of structure captures and removes organic debris. Regular removal of accumulated material is required because otherwise these materials will decompose and pass into the drainage.

The larger systems that have been developed over the past several years are generally intended for installation in new catch basins or inlet boxes, with one or more compartments for settling, filtration, oil separation and other NPS removal processes. They can be effective in small catchments where the hydraulic loading is limited, but the associated operation and maintenance can be significant. Highly urbanized communities adjacent to waterways have found that they are the only possible methods of reducing NPS loadings. At UNC-Chapel Hill, the existing infrastructure analysis has identified several portions of existing infrastructure that may require reconstruction. In these situations it may be reasonable to include some larger water quality measure as part of the structural replacement and new construction.

Rain Gardens and Tree Trenches

Both Rain Gardens and Tree Trenches are efficient in removal of most NPS, through the filtration of water through the soil and the uptake of pollutants by micro-organisms on the plants and by the plants themselves. Related environmental benefits, such as atmospheric reduction of CO2, moisture returned to the atmosphere, habitat value and overall improvement of campus aesthetics are also important considerations in any strategy for environmental sustainability.

Runoff Capture and Re-use

Runoff Capture and Re-use systems collect rainfall in the immediate vicinity of the impervious surfaces and store and re-use that water. Irrigation, cooling and sanitary supplemental flows have all been considered as possibilities for re-use and should result in a decreased demand for treated potable water for these uses. Capture, Storage and Re-use systems are shown with 100% pollutant removal since re-use will prevent direct conveyance.

Landscape Conversions

A number of measures are recommended that would change the remaining undeveloped portions of the campus into landscape cover types that produce less runoff and require little if any application of chemicals. Like Rain Gardens and Tree Trenches, Land Cover Conversions offer water quality benefits, but because the overall reduction in runoff volume is relatively small, the net water quality benefit is limited.

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S T O R M W AT E R M A N A G E M E N T R E C O M M E N D AT I O N S

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5.0 STORMWATER MANAGEMENT RECOMMENDATIONS

5.1 INTRODUCTION

This final chapter focuses on stormwater management recommendations for the evolving campus. It identifies specific actions in specific locations that will achieve the greatest possible volume reduction and water quality benefits. These benefits are compared with the requirements for volume reduction under the Town of Chapel Hill OI-4 Zoning Ordinance. Problems of flooding on campus were also considered and a special study was added to this report to analyze in detail the flood flows through the pipe system in ME-1, one of the most highly urbanized portions of the UNC-Chapel Hill campus. For these situations, the volume of storage for rate reduction is as important as the net volume reduction for watershed management, even though with most detention measures the stored runoff is simply released within the drainage following peak runoff periods.

Lastly, this chapter will describe a number of case studies/pilot projects which use combinations of the proposed BMPs working together. These projects include those that have already been constructed, those presently in design, and those that may be designed and realized in the future. For projects considered in detail, the BMPs selected have evolved and in some cases changed over time. During construction and subsequently in operation each project should be monitored to evaluate its effectiveness and to determine solutions to any problems. Knowledge gained from this monitoring should be used to improve future designs.

5.2 BMP APPLICATIONS BY WATERSHED

Stormwater volume reduction requirements under the Town of Chapel Hill OI-4 Zoning ordinance represent only a small percentage of the total runoff volume presently generated by the existing, developed campus. In the Meeting of the Waters watershed where a number of new projects are planned or being built, the volume reduction requirements under the Town Ordinance are 138,160 cubic feet, or 3.2 acre feet—only a 3.9% increase over existing conditions. In comparison, the total runoff presently produced by this watershed in a 2-year rainfall is 3,416,740 cubic feet, or 78 acre feet.

Stormwater mismanagement is the largest cause of stream deterioration across the country. The reason for going beyond the requirements of the Town Ordinance is that campus streams and waterways will never be restored to healthy, functioning systems without additional stormwater measures. UNC-Chapel Hill’s commitment to innovative, alternative stormwater management on campus is the first step in bringing these “impaired” streams and waterways back to life. With this in mind, the Stormwater Management Plan presents both presently approved BMP additions to new campus projects (Table 5.4: Stormwater Projects: Implementation Plan) as well as a wide variety of recommendations for BMPs that in some cases will stand alone (Table 5.2: potential BMPS all campus watersheds Eight-Year Development Plan).

The Town of Chapel-Hill Ordinance, forward thinking as it is, does not solve existing stormwater problems; it only prevents them from getting worse. However, most stormwater ordinances do not ever achieve this result and this ordinance has been held up as a national model for stormwater management at the EPA National Conference on Low Impact Development at the University of Maryland, University Park, MD. September, 2004.

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Table 5-1

VOLUME COMPLIANCE with TOWN OF CHAPEL HILL OI-4 ORDINANCE 2- YEAR FREQUENCY RAINFALL

Watershed Drainage Existing 8-year Mitigation Percent Area Runoff Runoff Volume

Volume Volume Required (Acres) (CF) (CF) (CF)

Battle 139.9 688,500 688,650 150 Bolin 30.9 279,510 282,630 3,120 1.10% Chapel 78.1 283,050 282,980 -70 Mtg Waters 441.3 3,416,740 3,554,900 138,160 3.89% Morgan 49.9 363,440 394,430 30,990 7.86%

Table 5-1 shows the estimated volume reduction requirements for the 2-year rainfall under the Town of Chapel Hill’s OI-4 Zoning Ordinance. In terms of stormwater volume reduction by watershed, the potential total benefit is well in excess of regulatory requirements, except for Morgan Creek. However, substantial additional BMPs will be required to reduce runoff volume in this watershed to mitigate downstream impacts.

In Meeting of the Waters watershed, the largest watershed on campus, the potential to reduce runoff volume is much greater than that required under Town criteria. Much of this potential is found within the eastern-most tributary of the watershed, in sub-watershed ME-3, where the various play fields are located. In contrast, few large volume reduction BMPs are possible in the western portion of the watershed in sub-watershed ME-2. On the other hand, the central part of the larger watershed, sub-watershed ME-4, includes several major new projects, such as Rams Head, Ehringhaus Field and the Bell Tower, all of which have the potential to provide significant volume reduction.

UNC-Chapel Hill has the potential to reduce runoff volume by a far greater amount than is required by the Town. With this excess capacity it should possible to select only the least expensive option or set of measures. In fact, this is not possible, because the analysis of existing conditions at the UNC-Chapel Hill campus (before completing the Eight-Year Development Plan), reveals a highly disturbed and impervious watershed, with severe runoff impacts at present. Figure 5-1 compares the runoff volume produced within Meeting of the Waters—the major campus watershed—over time. It shows runoff produced during the 2-year rainfall in four different time periods—a base line condition of pre-development forest cover; development in the early 1940’s; present runoff conditions; and run-off volume anticipated under the Eight-Year Development Plan. In Figure 5-1 the volume reduction benefits of BMP implementation are shown in green.

Figure 5-2. STORMWATER INFRASTRUCTURE IN SWMM MODEL STUDY AREA

Figure 5-1 COMPARISON OF 2 YEAR STORM VOLUME IN FOUR DIFFERENT TIME PERIODS

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VAN HECKE LAW PARKING LOT Porous pvmt. Storage/infilt. 18,112 10,867 BOSHAMER TENNIS COURTS Porous pvmt. Storage/infilt 37,063 22,238

FETZER FIELD Runoff reuse 74,959 11,244

BAITY HILL PARKING DECK Roof Garden 88,237 20,295

CARDINAL & DOGWOOD Green Canopy 294,085 41,186PKG. DECKS

CRAIGE PARKING DECK Green Canopy 93,584 13,102

ENTIRE WATERSHED Tree Trenches 50,021 15,006

ENTIRE WATERSHED Rain Gardens 359,060 17,055

ENTIRE WATERSHED Lawn to. 275,185 11,007 Successional las

ENTIRE WATERSHED Lawn to planting 732,097 36,605

WATERSHED TOTALS 2,705,808 1,179,141

BATTLE CREEK WATERSHED STEELE PARKING LOT Porous pvmt. Storage/infilt 9,000 5,400 CALDWELL PARKING AREA Porous pvmt. Storage/infilt 19,500 11,700 COKER CISTERN Runoff reuse 491 2,900 ENTIRE WATERSHED Rain Gardens 68,391 3,249 ENTIRE WATERSHED Lawn to Planting 132,782 6,639 ENTIRE WATERSHED Forest Restoration 49,998 2,000 ENTIRE WATERSHED Rough grass to meadow. 6,396 192 WATERSHED TOTALS 286,558 32,080

Table 5-2 POTENTIAL BMPsALL CAMPUS WATERSHEDS, EIGHT-YEAR DEVELOPMENT PLAN PROJECT BMP TYPE SIZE OF BMP VOLUME REDUCTION (square feet) (Cubic Feet)

MEETING OF THE WATERS RAMS HEAD BUILDING Roof Garden 40,174 11,249 EHRINGHAUS FIELD Infiltration Bed 48,179 46,000 CARMICHAEL FIELD Infiltration Bed 22,000 72,000 SCIENCE CENTER Phase I Infiltration Bed CARRINGTON HALL Roof Garden 4,173 960 BOSHAMER FIELD Infiltration Bed 40,000 286,000 NAVY FIELD Infiltration Bed 56,911 34,147 NORTH FIELD Infiltration Bed 55,691 33,415 WINSTON CONNOR Porous AC pvmt. 16,047 9,628 PARKING LOT STADIUM DRIVE Porous AC pvmt. 51,247 30,748 WILSON-DEY PARKING LOT Porous AC pvmt. 9,021 5,412 KENAN STADIUM Storage/Reuse 108,965 360,000

SCIENCE COMPLEX Roof Garden 18,000 4,140 BELL TOWER PARKING DECK Roof Garden 47,280 10,874 HOSPITAL PARKING DECK Roof Garden 63,427 14,588 CRAIGE DORM COURT Infiltration bed 3,013 1,808 FIELD HOCKEY ASTROTURF Infiltration bed 74,261 44,557

KOURY NAT. PARKING LOT Porous pvmt. Storage/infilt 25,016 15,010

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MORGAN CREEK WATERSHED GENETIC MEDICAL PLAZA Infiltration Bed 54,227 17,195

ACC PARKING LOT RETROFIT Infiltration trenches 11,723 3,869 ACC Runoff reuse 7,500 31,000 ENTIRE WATERSHED Tree Trenches 16,887 5,066 ENTIRE WATERSHED Forest Restoration 200,646 8,026 ENTIRE WATERSHED Lawn to Planting 111,853 5,593 WATERSHED TOTALS 402,836 70,749

BOLIN CREEK WATERSHED ARTS COMPLEX Roof Garden 31,000 7,130 ENTIRE WATERSHED Rain Gardens 33,210 1,577 WATERSHED TOTALS 64,210 8,707

Table 5-3

ACREAGE OF PROPOSED STRUCTURAL BMPs

• Permeable Pavements with Storage/Infiltration 1.93 Acres • Other Surfaces with Storage/Infiltration 7.75 Acres

• Vegetated Roof Systems and Roof Gardens 2.69 Acres • Street Trees in Continuous Trenches 1.64 Acres • Lawn Conversion to Rain Garden 9.91 Acres • Impervious Surface Conversion to Rain Garden 1.53 Acres • Planted Areas Conversion to Rain Gardens 6.06 Acres

• Retrofit Parking Islands to receive stormwater run-off with 0.19 Acres § Infiltration trenches

§ Bio-swales • Surface Ponds and Wetlands for treatment and storage 0.53 Acre

TOTALS 11% of Campus 32.23 Acres

PROPOSED STORMWATER MANAGEMENT MEASURES: IMPLEMENTATION PLAN

Project Name EstimatedConstruction

Cost

Soft Costs:

EstimatedTotal Cost

StormwaterFunding

Implementation Strategy

Criteria Code

1 Global Education Center

$392,000 $98,000 $490,000 $350,000 Add to Capital project

SWM

1 Hanes Hall Cistern $62,300 $15,575 $77,875 $77,875 Add to R&R project

SWM

1 Medical Drive Cistern/walkways

$90,000 $22,500 $112,500 $112,500 Andropogon/ Cahill

SWM

1 Coker Woods - Raise dam

$50,000 $12,500 $62,500 $62,500 A&E SWM

1 Davis Library Rain Garden


D

1 Steele/Caldwell Parking Lots (50,000 SF)


SWM & T

1 North Campus Pipe Replacement Projects

$475,000 $593,750 $300,000 Part of Steele/Caldwell lots

I

1 North Campus Pipe Camera Investigation

$52,080 A&E I

1 Water Quality Inlets $40,000 $10,000 $50,000 $50,000 A&E SWM

1 ME-2/ME-5/MO-1 SWMM Study


SWM

1 School of Govt. flooding

$60,000 $15,000 $75,000 $75,000 Rose Group I

1 AOB Flooding $60,000 $15,000 $75,000 $75,000 Corley Redfoot Zack

I

Table 5-4

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1 Pipe Replacement, Bowles Drive

$400,000 $500,000 $400,000 Add to Res Phase 2

I

1 Science Center Phase II

$325,000 $81,250 $406,250 $200,000 Add to Capital project

SWM

1 Bell Tower Storage $1,200,000 $1,500,000 $1,500,000 Add to Capital project

SWM

1 Navy Field Infiltration Bed


T

Subtotal $5,100,848 $4,064,955

2 Arts Common Green Roof

$289,885 $72,471 $362,356 Add to Capital project

2 South Road/S. Columbia Street Trees/Rain Gardens

$150,000 $37,500 $187,500 Andropogon

2 Peabody, Miller, ACW, Carolina Inn Rain Gardens

$100,000 $25,000 $125,000 Andropogon

2 Mitchell Hall Storage/Infiltration Bed

$0 $0

2 Boshamer Field $2,184,000 $2,730,000

Subtotal $3,404,856

3 Genetic Medicine Plaza

$379,592 $94,898 $474,490

3 ACC Parking Lot Retrofit

$97,127 $24,282 $121,409 Andropogon

3 Stadium Drive Beds

$409,975 $512,469

3 North Field Infiltration Bed

$389,839 $97,460 $487,299

3 Cardinal & Dogwood Decks

$1,603,311 $2,004,139

3 Craige Deck $510,030 $637,538

3 Bell Tower Green Roof

$1,040,165 $1,300,206

Subtotal $4,237,343

Funds already spent or committed:

Carmichael Field $1,136,300 Completed in 2002

Ehringhaus Field $1,000,000 Under Construction

Ramshead Green Roof

$1,000,000 Under Construction

Wilson Dey Infiltration Bed

$0 Under Construction

Carrington Hall Green Roof

$0 Under Construction

Manning Drive Pipe Replacement

$1,200,000 Design Underway

Bell Tower 100-yr. flood modeling

$20,000 Cahill

Design Fees $1,553,745 Andropogon/ Cahill/ Rose Group

Subtotal $5,910,045

TOTAL $12,743,046 $9,975,000

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5.3 ADDITIONAL BMP RECOMMENDATIONS TO MITIGATE LOCAL FLOODING

While the BMPs summarized in Table 5-2 will mitigate the volume increase resulting from the Eight-Year Development Plan, there remain localized flooding problems on campus. Sub-watershed ME-1 has experienced flooding at a number of locations over the years, as the amount of impervious cover has increased and the storm sewer pipes designed for individual local flow conditions, were overwhelmed by upstream discharge. This “surcharging” of the storm sewers is a result of the rate of flow or “hydrologic conveyance”, exceeding the ability of the pipes to carry the water.

ME-1 is an area of campus where flooding problems are severe. The University was concerned about the ability of the new storm sewers being constructed under Rams Head to carry the flood peaks in both the 10 year and 100 year storm. In response to this concern, an initial hydrologic and hydraulic study and special flood routing analysis of sub-watershed ME-1, was added to the overall Stormwater Management Plan, (Figure 5-2).

Figure 5-2 PLAN OF UNC-CHAPEL HILL CAMPUS SHOWING THE LOCATION OF ME-1, THE HYDROLOGIC AND HYDRAULIC MODEL ANALYSIS STUDY AREA

FUNDING $9,975,000

Criteria for Prioritization:

Code

Infrastructure Replacement or Repair

I

Contribution to Stormwater Management Plan

SWM

Demonstration -- “Pilot Project”

D

Timing T

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The storm sewer system was modeled using the United States Environmental Protection Agency (US EPA) hydrologic model known as SWMM (Stormwater Management Model). This model is actually several models. The 83-acre sub-watershed area was sub-divided into 27 small drainage catchments, and the runoff and peak rate of flow was estimated using the SCS Cover Complex Method and compared to the hydrographs developed with the SWMM model. The 10-year and 100-year frequency rainfalls were simulated along with the measured rainfall from Hurricane Fran. The individual hydrographs were routed through the major pipe elements using the Runoff Module of SWMM. Probable flooding locations were identified in the storm sewers. A more detailed analysis of stormwater flows was then made using the EXTRAN (Extended Transport) Module, which assessed surcharging conditions, developed hydraulic grade lines, evaluated the existing piping system and formulated possible solutions, (Figure 5-4).

Figure 5-4 SWMM MODEL

As the model analysis indicated possible problem locations, various BMPs were evaluated at or above these locations to reduce or detain runoff volume. For both the 10 year and the 100 year storms, the volume of water required to prevent flooding was estimated. A series of BMPs were analyzed, including all of the measures described in Chapter 4, as well as several new measures, to be located at or above critical junctures. These new BMPs were added to the overall program for stormwater management, and are included in Table 5-3, Recommended BMP Measures.

A detailed flood flow analysis clarifies the cause and amount of the problem in the highly urbanized portions of the campus, where there has been localized flooding. For these situations, the volume of storage for rate reduction is as important as the net volume reduction for watershed management, even though with most detention measures the stored runoff is simply released within the drainage following peak runoff periods.

ME-1 was chosen as the study area because it is one of the most densely developed areas on campus, draining through three main storm sewer lines to a juncture directly above the stadium. It is 83-acres and includes the area south of Cameron Street, west along South Columbia Street and the upper end of Kenan Stadium as shown in Figure 5-3.

Figure 5-3 ME-1 SUB-WATERSHED SHOWING EXISTING UTILITY INFRASTRUCTURE AND THE DIVISION INTO 27 CATCHMENT AREAS FOR STUDY PURPOSES

As a result of this study, additional BMPs are recommended for sub-watershed ME-1 and are included in this chapter of the Stormwater Management Plan. The main recommendations of this study are to provide enough detention to reduce surcharging in the existing pipe system. However, detention will not significantly reduce volume or improve water quality.

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Although the model analysis focused on flooding during the 10 year and 100 year storms, and led to stormwater measures that mitigate peak rates, the opportunity for any BMP to address issues of volume reduction and water quality improvement should always be considered. Vegetation measures such as Rain Gardens, or storage/infiltration measures such as Infiltration Trenches can also be used when appropriate. Additionally, traditional rate control measures, such as storage in perforated pipes will allow gradual infiltration in small storms. However this type of storage must be used with caution to avoid flooding basements. The idea of “leaky pipes” is often a good one in the right location, and volume reduction means less water downstream.

The University intends to complete a more detailed rate and flood flow analysis in the future within other campus watersheds.

5.4 SPECIFIC RECOMMENDATIONS TO MITIGATE FLOODING

In looking for solutions to prevent and reduce downstream flooding, the analysis began at the top of the sub-watershed, Within the ME-1 sub-watershed a number of locations were reviewed to evaluate their potential for BMPs that would reduce flooding. The following descriptions of proposed campus projects and recommended measures within each project are intended to address this issue, as well as to reduce the flow rates in the pipes beneath Keenan Stadium.

WESTERN PORTION OF ME-1

Beginning at the western most side of campus, flooding has been observed along McCauley Street and at the Science Complex.

Global Education Center

The Global Education Center is currently under design, and includes a number stormwater management BMPS, but there is also the opportunity at this project to increase the size, variety and numbers of stormwater management measures.

The Global Education Center provides a major opportunity to reduce the flows to McCauley Street. It is recommended that the stormwater detention capabilities be increased to 20,000 cubic feet of storage in a 10-year storm event, with a peak discharge downstream of the project area of 12 cubic feet per second. Stormwater management here can take the form of a variety of measures, including a green roof, underground cisterns/storage, or pipe storage along the alley. The combination of two or more measures will create greater benefits if one of the measures provides detention along the existing alley, intercepting runoff from the Tate Turner Kuralt Building. The effect of this storage on the 10-yr storm hydrograph at McCauley and Pittsboro is to reduce the peak rate by 65% from 15.9 to 5.6 cubic feet per second and delay it by almost 10 minutes.

Whitehead and Miller Lawns

The lawn areas in front of Whitehead and Miller provide opportunity for stormwater management in the form of Rain Gardens and Storage/Infiltration Trenches. Rather than one element, several small measures located as opportunity allows and designed to overflow to the storm sewers, can provide reduction in the flows and flooding along McCauley Street. These measures also reduce the flow rates at Venable. The Rain Gardens should be designed to act

as small, very shallow detention facilities, with a low flow discharge and appropriate plantings, essentially creating “puddles” in extreme storm events. A total volume of 4,700 cubic feet of storage is recommended, or approximately 3,600 square feet of Rain Gardens. The effect of this storage, combined with the Global Education Center storage (since it is upstream) on the 10-yr storm hydrograph is to reduce the peak rate by 57% from 30.4 to 12.9 cubic feet per second and to delay water arriving at this location by almost 10 minutes. These measures will eliminate the flooding along McCauley Street during the 10-year storm.

Carolina Inn Area

Behind the Carolina Inn, there appears to be opportunity for the installation of an Infiltration Trench or other similar measure. Like the recommendations for the Whitehead and Miller lawns, this measure would reduce flows at McCauley Street and at Venable. A small rain garden of 900 cubic feet is recommended in this area.

Off-Campus Areas

Although the residential area on McCauley Street (across from the Carolina Inn) is not mapped as part of the drainage to Meeting of the Waters, it appears that this area may possibly drain down McCauley Street and onto the campus. In this area, both roof drains and other impervious surfaces discharge to the curb gutter and flow from the crest of the hill to the intersection, where surface inlets appear to connect with pipe elements on the southeast corner, and thence along McCauley Street toward the low point at Venable.

The streetscape along McCauley Street offers a unique opportunity to reduce this runoff by the construction of Infiltration Trenches beneath the sidewalks, with the walks reconstructed in open graded brick or retained as gravel, if desired. Roof leaders could also be mitigated by these simple trench/beds, and the road drainage itself could be included with the use of water quality inlets. As a cooperative measure between UNC and the town, this could serve as a model effort to better manage stormwater impacts. A program of cost sharing could support this construction, and the overall improvement could be considered a municipal investment as well as a campus measure, with both parties receiving benefit. While this opportunity is not included in the model analysis, it is presented here for future consideration, and as another measure to reduce flows on McCauley Street.

Peabody

In the northern portion of the drainage area, above the Science Complex, the model analysis indicates that there is an existing 12-inch diameter pipe downstream of Peabody that is undersized for the flows from this very impervious area. Although flooding has not been reported here, there is an opportunity to install small measures such as Rain Gardens or Pipe Storage with a volume of 2,000 cubic feet. Such a BMP is recommended to reduce the peak flows. Because the model indicates that the undersized pipe is already “detaining” flows, there is limited downstream benefit in terms of flooding. The recommendation is primarily to reduce local surcharging. However, because Rain Gardens have additional water quality and volume benefits, their implementation is encouraged. During a 10-year storm event, this storage reduces the peak flow rate of sub-area 1 from 9.5 to 6.1 cubic feet per second and eliminates the predicted surcharge.

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Science Complex Phase I

The Science Complex Phase I project included stormwater management in the form of storage/detention/infiltration beds that provide a total of approximately 17,600 cubic feet of storage. This measure is not a recommendation (as the improvement is under construction). It was incorporated into the model analysis so that the benefits of this measure were considered. During a 10-year storm event, the Science Complex stormwater beds reduce the peak flow rate from the entire upstream drainage area from 26.1 cubic feet per second to 13.3 cubic feet per second, a substantial reduction.

Science Complex Phase II

Phase II of the Science Complex provides additional opportunities for stormwater management, and in light of the flooding in the area of Venable, stormwater management is required. It is recommended that Phase II of the Science Complex provide a minimum storage/detention capability of 20,000 cubic feet. Similar to the Global Education Center, this may take the form of several measures as appropriate to the project, including the use of a simple green roof, vertical storage, cisterns, and underground pipes. If additional storage can be incorporated into the project cost-effectively it is encouraged. This storage reduces the 10-yr peak flow rates from sub-area 11 by 83% (from 16.2 to 2.8 cfs) and delays the peak by 18 minutes.

In addition to providing stormwater management as part of this project, it is suggested that the University evaluate the opportunity to redirect the storm sewer to avoid the low area in front of Venable, and instead convey upstream flows in a new storm sewer along South Road. The existing storm sewers were probably placed in the historic streambeds, and a low point exists at Venable where the pipes are near to the surface and flooding occurs. All of the upstream drainage is conveyed through this area. While the above recommendations should eliminate flooding in the 10-year event, a further recommendation would be to relocate the pipes so that the upstream drainage is not conveyed through this area. This involves a new storm sewer from below Catch Basin 3177 to Catch Basin 2313. Preliminary evaluation of existing utilities and grades indicates that this option may be feasible. This is similar to the approach taken at the Rams Head project, where upto 21 acres of drainage area were diverted around the new building instead taken underneath it.

Additionally, it appears that the area in front of Kenan Labs was designed to provide stormwater management, or at least to handle flooding as it occurs in this area. In the model analysis this area is considered as a small detention area, and the only recommendation is to verify that this area was intended for small, localized stormwater management.

EASTERN PORTION OF ME-1

The eastern drainage area along South Road originally drained towards Fetzer Gym, and was redirected towards the Stadium drainage area because of flooding problems. The storm sewers from this 11-acre area appear to go against grade, and consequently are rather deep. Consideration was given to re-directing this sub-area back to its natural drainage, but the opportunities are limited and expensive. In this analysis, this option was evaluated but not included in the BMP recommendations.

Alexander-Conner-Winston

The model analysis only indicates flooding during the 10-year event at the corner of South Road and Raleigh, and because the details on the storm sewers are limited in this area (and a number of assumptions have been made), potential flooding in the 100-year storm is uncertain. To address this flooding, and reduce overall flows to the Stadium, 2,000 cubic feet of stormwater management in the form of Rain Gardens, Beds beneath walkways, and Infiltration Trenches is recommended in the Alexander-Conner-Winston area. This area appears to provide opportunities for such measures, while there are few remaining available locations along South Road.

Additionally, the walkways, paths, and lawn areas provide other locations for similar measures, although these measures have not been considered in the model. As improvement or restoration is undertaken in these areas, it is recommended that stormwater measures be included.

PORTION OF ME-1 ABOVE THE STADIUM

Coker Woods

All of the areas discussed above, eventually drain into Coker Woods, and then under the Stadium. Coker Woods, a naturally shaped small bowl, is the last remaining unburied stream segment in the drainage area. Three pipes discharge into the woods, and a single 42-inch pipe conveys all of the flows out and back into the storm sewers. This 42-inch pipe and headwall was recently rebuilt as part of the Stone Center project.

The model analysis indicates that during large storm events such as the 10-year storm, the 42-inch pipe cannot convey all of the flow that the three incoming pipes discharge into Coker Woods. The woods, in effect, presently serve as a detention basin. This has considerable downstream benefits in mitigating flooding. The following minor recommendations are intended to assure that this area can safely continue to function.

1. The current configuration is an open pipe at the headwall, which in extreme events could clog from fallen trees or debris, modification to the outlet to reduce this possibility is recommended. This could include some control for retention of smaller storms, as well as an overflow that is not easily clogged during extreme events.

2. Slightly raising the existing headwall by three feet and verifying waterproofing will prevent any overtopping of the wall during the 10-year event with other recommended BMPs in place. During the 100-year event, the wall is slightly overtopped and appears (and is modeled) to run overland to the next inlet. The as-built grades in the Stone Center area should be confirmed and evaluated to assure that the facility will not experience damage.

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SOUTHERN PORTION OF ME-1

The following measures are intended to reduce the flows that ultimately drain through the Bell Tower Parking Lot area and combine with the flows from Coker Woods to flow beneath Kenan Stadium.

South Columbia near Wilson

Much of the drainage along South Columbia Street makes it way towards the intersection in front of Wilson, which is scheduled for improvement and reconstruction. As part of this effort, it is recommended that stormwater management be incorporated into the improvement efforts. A volume of 5,200 cubic feet, in the form of sub-surface pipes and storage, Rain Gardens in front of Wilson, or other measures is recommended.

Beard/Public Health Area

In this area, there are again opportunities for stormwater management in the form of Rain Gardens, storage beneath walkways, and Infiltration Trenches. A total volume of 5,000 cubic feet is recommended in this area.

Medical Drive

Within sub-area 18 there are existing storm sewers both along Medical Drive and in front of Mitchell. A partially buried cistern, located along the wall area of Medical Drive, or a storage pipe or cistern in this area provides significant peak rate reduction. A storage volume of 7,700 cubic feet is recommended.

Mitchell

There are existing parking areas adjacent to Mitchell and upstream of the Bell Tower area that can serve as sub-surface storage areas. These areas should be examined in detail to determine the preferred location for stormwater in terms of existing roof leaders and connections, a volume of 7,500 cubic feet is recommended in this area.

Bell Tower Building

The proposed Bell Tower building is intended to be a multi-function facility, providing parking capacity for 1,600 vehicles in a multiple deck structure, a 25-thousand ton chilled water plant and a Science Laboratory Building of 200,000 SF capacity. Since this structure will effectively overlie an existing surface parking area which is totally impervious, the resultant net increase in stormwater generated by the structure will be close to zero. Additional roadway construction will add slightly to the total net impact. Under the Town of Chapel Hill Stormwater Ordinance requirements, the reduction in runoff volume during the 2-year frequency rainfall will be minimal, and the resultant water quality produced from the building structure should be significantly less than the present pavement parking site.

The responsibility of the Bell Tower building is not only for its own footprint. The combined inflows from the 4 different segments of sub-basin ME-1 produces a peak flow of concern above the stadium. Only 2 of the 4 flows go directly under the proposed Bell Tower building footprint but all 4 contribute to the problem of potential flooding at the stadium. New modeling analysis is re-examining the impact of this project on the potential for flooding above the stadium.

However, the use of this new facility to significantly reduce the impact of stormwater runoff from the 83-acre drainage above the stadium is absolutely critical, and in fact offers the single greatest opportunity to reduce both the volume and the resultant rate of runoff responsible for the potential flooding above the stadium. In addition, the new construction will totally replace and reconstruct the existing storm sewers situated beneath the pavement, conveying runoff from the west and southwest catchments of sub-watershed ME-1.

The model analysis indicates that a volume reduction on the order of 55,000 CF is required to meet the flow capacity of the existing storm system down gradient of the new building site during the design rainfall. While this is a significant volume, in light of the 2.5-acre footprint of the project it is not unreasonable. If opportunity allows, it is recommend that additional stormwater capacity be incorporated into the project. If this storage is incorporated into the design of the Bell Tower building, the WBE model predicts significant benefits. During a 10-yr storm, there is the potential to reduce the peak from sub-area #20 by 81% or 23.5 to 4.5 cubic feet per second, to reduce the peak from sub-area #25 by 48% or 18.2 to 9.4 cubic feet per second, and to considerably reduce and delay the peak from the entire southern drainage area to the stadium, while preventing localized surcharges.

The new structure is assumed to include a “roofprint” of 99,000 square feet. During a 2-year rainfall (3.6”/24 hours), this area will receive 29,700 cubic feet of rain, and during the 100-year rainfall the total will be 66,000 cubic feet. The model analysis indicates that the greatest peak flow reduction downstream can be achieved by capturing the total runoff from the project area. By designing the building to capture the rain that falls upon the roof, and either return it to the atmosphere, hold it in short term storage, or reuse it as a raw water source in the chiller system or surrounding irrigation, the required peak rate reduction can be achieved. It may ultimately be determined that all three solutions are both feasible and desirable from both an environmental and fiscal perspective.

It will also be possible to capture and store a portion of the upland runoff from the contributing landscape in the west and southwest drainage areas, but the existing plumbing system is deep relative to the potential storage areas adjacent to or within the new structure, and will be significantly more polluted, especially during heavy rainfalls. The use of internal space for stormwater storage could be an expensive option with minimal cost benefit, but warrants detailed consideration in the Concept Development process.

The roof area presents the best opportunity to capture rainfall in a relatively unpolluted condition, but the use of the upper surface as a parking deck introduces major water pollution potential. One solution would be to design a vegetated canopy system, with partial volume reduction by evapo-transpiration and partial detention storage within the vegetated roof system. A simple green roof system can capture and return up to 65% of the annual rainfall (29 inches/year) to the atmosphere, with the overflow conveyed to vertical storage units configured within the roof drain system. Storage units would be located at each point of vertical drainage, and could be constructed in plastic, metal or fiberglass. The advantage of vertical storage is that the stored rainfall has the ability to discharge at the ground surface without additional pumping, and if used for irrigation, could be applied without energy costs.

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It is assumed that the three upper roof areas would not be available for any type of vegetated system, and so this runoff could go directly to the vertical storage units or to the canopy over the parking deck, depending on the potential value and need for reuse. Since the opportunities for reuse are significantly greater during the 20-week growing season and similar cooling season, the final capture and storage system could be flexible, with capture/retention varying with actual rainfall conditions.

A storage chamber could also be built within the building itself, but the economics of this option should be carefully considered, since the loss of functional space within the structure would be a negative consideration. In addition, any retained storage at ground level or below requires pumping, even for slow release to the storm sewer system, and may be prone to failure during storm events. Although not considered in the model application, there also appears to be an opportunity to store or divert a considerable amount of runoff under the proposed new driveway entrance to the Bell Tower building.

5.5 CASE STUDIES / PILOT PROJECTS DEMONSTRATING BMP APPLICATIONS

As the Eight-Year Development Plan has evolved over the past three years, a number of projects have used at least one or more of the BMPs recommended in this study. A number of other development projects, presently in the planning and design stages, also intend to incorporate these recommended measures. Table 5-3 summarizes these current projects for Meeting of the Waters watershed and compares the probable volume reduction of these projects to the volume reduction with the comprehensive stormwater management program described.

As the stormwater program has evolved at UNC-Chapel Hill the University has made a very strong commitment to the implementation of many of the stormwater management measures discussed in this report. The following Case Studies/Pilot Projects highlight specific stormwater applications that have been considered in detail. Several of these have already been constructed such as Carmichael Field, The Friday Center and Estes Remote Parking Lots, Rams Head and Ehringhaus Field.

CASE STUDY 1 | Permeable Pavement with Storage/Infiltration Beds at the Friday Center Park and Ride Lot and the Estes Drive Storage Parking Lot

The Friday Center and the Estes Drive Parking lots are the first applications of permeable paving at UNC-Chapel Hill and the first large-scale application of permeable pavement in North Carolina. As described in Chapter 4, this BMP is a system that combines a water permeable pavement surface over a storage bed filled with uniform aggregate to hold water and provide structural support. The stone bed provides a 40% void space for holding stormwater. This BMP also allows slow infiltration of stormwater into the ground beneath where soils permit. It assumes that this system is capable of infiltrating the total amount of rain during 95% of all rainfall events annually.

Both these parking lots were paved with an area of pervious asphalt as well as an area of permeable concrete. Installing both types of surface will allow the University to monitor and record the maintenance, long-term performance, and overall costs, of each.

Both lots also include a stepped bed system to minimize stone bed depth and maximize infiltration surfaces. These beds are sized for the 2-year storm volume and will mitigate the peak flow in larger storms with the result that total site runoff on the paved, post development site, is actually less than total site runoff on the wooded predevelopment site.

Figure 5-5 FRIDAY CENTER PARK AND RIDE LOT, AERIAL AND GROUND VIEWS SHOWING PERMEABLE CONCRETE, PERMEABLE ASPHALT, THE AERIAL PHOTOGRAPH ALSO SHOWS THE PORTION OF THE PARKING LOT WHERE THE OLD PAVEMENT WAS RE-SURFACED. THIS PAVEMENT RUNS OFF INTO THE SURROUNDING LAND.

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CASE STUDY 2 | Alexander Connor Courtyard with Infiltration Trenches

Because the new Town ordinance mandating no increase in volume run-off for the 2-year, 3.6” Storm would apply to this project, this case study was developed to illustrate how the increase in stormwater runoff could be handled on this particular site. Designs included three layout options for infiltration trenches and beds in the courtyard area of the dormitory.

Figure 5-7 PLACEMENT OF UNDERDRAINS

Figure 5-8 INSTALLATION OF PERMEABLE ASPHALT PAVING

Figure 5-9 BUCKETS TRAP SOLIDS TO IMPROVE WATER QUALITY

Figure 5-10 FINISHED PARKING LOT AT FRIDAY CENTER DURING A RAINSTORM OF 6.5 INCHES

Figure 5-6 INSTALLATION OF BED LINER

Figure 5-11 COURTYARD WITH HISTORIC STREAM

Figure 5-12 INFILTRATION TRENCH PROFILE

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CASE STUDY 3 | Carmichael Field

The UNC-Chapel Hill Intramural Field #3 Drainage, Water Storage & Irrigation Project includes a subsurface stormwater infiltration bed beneath the Athletic Field. This BMP stores runoff from the field and the surrounding drainage area for re-use and infiltration. Stormwater drains into a large stone bed underneath the playing field, from an upland drainage area. This area includes the intramural field above the storage system, the east half of the adjacent artificial turf playing fields, the indoor track east roof above the classrooms, most of the Institute of Government roof area, the Institute of Government Parking Deck, and South Road from the entrance road to Carmichael Gym to the parking deck entrance ramp, as well as approximately half of the South Road graveyard. The bed provides storage capacity of 73,000 cubic feet of runoff. Stormwater from the bed is conveyed to a wet well with a submerged pump and controller which allows water to be pumped from the wet well to an intramural field irrigation system.

In addition to the stormwater storage and potential re-use of the water for irrigation , the design of this system at Carmichael Field includes BMPs to clean the water. Stormwater from existing pipes is directed into two solids separator units located at the north and south ends of the intramural field. These units consist of three chambers, the first with a cylindrical stainless steel insert to cause the water to spin with centrifugal force, enabling solids to settle. The next two baffled chambers allow additional floatables as well as solids which may have passed through the first chamber to settle. Each unit has two manholes to enable solids to be removed by septic tank pump trucks. Baskets are in place in other pipes draining into the stone bed to separate out solids. These baskets need to be emptied periodically so as not to impede water flow. Since this project was built in 2002, operation and maintenance costs should be closely monitored to evaluate performance versus cost.

Figure 5-16 CONTAMINATED MATERIAL WAS REMOVED FROM THE SITE.Figure 5-17 APPROXIMATELY 550,000 GALLONS OF STORAGE IS AVAILABLE WITHIN THE STONE BED.Figure 5-18 OFFSITE DRAINAGE WAS TREATED TO REDUCE SOLIDS, OILS, AND METALS.Figure 5-19 INTRAMURAL FIELDS 3 AND 4, IRRIGATED FROM SUBSURFACE STORAGE.

Figure 5-13 OPTION A UTILIZED AN EXISTING SAND VOLLEYBALL COURT FOR THE LOCATION OF A PROPOSED INFILTRATION BED. THE INFILTRATION BED WOULD HANDLE THE RUNOFF FROM BOTH ROOF LEADERS AND ADJACENT IMPERVIOUS AREAS, SATISFYING THE ORDINANCE REQUIREMENTS.

Figure 5-14 OPTION B PROPOSED AN INFILTRATION BED CREATED IN AN EXISTING LAWN AREA.

Figure 5-15 OPTION C ALSO PROPOSED AN INFILTRATION BED IN THE SAME AREA, BUT WITH NEW PLANTINGS THAT WOULD ALSO SCREEN THE VOLLEYBALL ACTIVITY, WHICH WAS A DESIGN GOAL FOR THIS PROJECT.

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CASE STUDY 4 | Rams Head Center and Ehringhaus Field

The Rams Head Center is a three story parking garage, surrounded on the south, east and west by a Campus Recreation Building and a Student Dining Facility. These buildings rise one and one half stories above the garage roof where a Roof Garden has been built, (Figure 5-22). The design of this Roof Garden includes cisterns to collect stormwater from the higher roofs to supply the irrigation system on the plaza, (also augmented by the UNC-Chapel Hill water supply). Stormwater storage will also occur in a layer of RainStore 3, a honeycomb of interlocking recycled plastic mini-storage containers, installed beneath the plaza (Figure 5-26 to Figure 5-28) This system provides both storage and transpo-evaporation.

Planting beds on the Plaza will absorb the first flush of runoff from the impervious surfaces, which include paved walkways and adjacent roofs. Roof leaders from the Campus Recreation Building and a Student Dining Facility are connected directly to perforated pipes below the finished grade of the plaza to help supply water to the lawn and plantings (Figure 5-24).

In addition to stormwater capture and reuse, as well as transpo-evaporation on the plaza, storage and infiltration is provided under Ehringhaus Field. Prior to the construction of the Rams Head facility, Ehringhaus Field was reconstructed as a temporary parking lot with a gravel surface. The existing soil was removed and a stormwater storage/infiltration system constructed beneath the temporary parking. This storage/infiltration system connects to the stream on the south side of the field (Figure 5-25).

When the garage is complete, the temporary parking lot will be demolished and the field restored with an irrigation system and turf sod. The stormwater infiltration system remains in place and the sod is established on a 12-inch layer of top soil.

Figure 5-20 CONCEPTUAL PLAN OF STORMWATER MANAGEMENT FOR RAMS HEAD CENTER

Figure 5-21AERIAL VIEW OF RAMS HEAD CENTER UNDER

CONSTRUCTION

Figure 5-22SECTION THROUGH PLAZA

SHOWING GREEN ROOF AND RECEIVING SWALE

IN LANDSCAPE FOR STORMWATER OVERFLOW

Figure 5-23CONCEPTUAL SECTION

THROUGH EHRINGHAUS FIELD SHOWING

STORMWATER STORAGE/ INFILTRATION SYSTEM

CONSTRUCTED UNDER TEMPORARY PARKING

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Previously buried and piped springs, surrounding the new buildings, will be “day-lighted” in a newly created stream. Extensive riparian corridor plantings will be installed along the banks to stabilize the slopes and establish a layered woodland at the edge of the channel. Coconut fiber logs will also be used to stabilize the stream banks. Large canopy trees, understory trees and shrubs provide shade for the stream channel and a separation between the riparian zone and the adjacent Athletic Field, (Figure 5-25).

Figure 5-24RAMS HEAD PLAZA WITH

“RAINSTORE” WAITING FOR INSTALLATION

Figure 5-25RAMS HEAD PLAZA WITH

“RAINSTORE” INSTALLED

Figure 5-26DETAILS SHOWING PLACEMENT OF “RAINSTORE”

CASE STUDY 5 | Coker Arboretum Channel Restoration/ Pond

Areas of the campus with important plant displays, like the Coker Arboretum, need water for irrigation and stormwater runoff can become a resource. The five-acre Coker Arboretum has an irrigation demand of 20,000 to 45,000 gallons of water per week to maintain its collections and displays.

The Arboretum staff had concerns about:• Erosion on the Arboretum grounds. • Conflicts of future stormwater management with a planned new irrigation system.• Conflicts with a new well was drilled for Arboretum for irrigation

A demonstration capture and reuse system that included treatment wetlands was designed to address those concerns and create a new landscape amenity for the campus in the low lying area on the common area south of McIver Hall where a small wetland already exists. The design does not preclude future development plans for the eastern edge of the common and is sensitive to existing large trees.

Coker Arboretum

Alderman Kenan

McIver

Figure 5-27THREE DIMENSIONAL PLAN OF THE CAMPUS SHOWING THE LOCATION OF COKER ARBORETUM

Figure 5-28CONCEPTUAL PLAN OF PROPOSED STORMWATER TREATMENT PONDS IN THE COKER ARBORETUM

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The stormwater management system captures stormwater runoff from roof leaders and direct rainfall, pumping this water back to the Arboretum for irrigation. Stormwater from this system would be first delivered to a pre-treatment catch basin and then to a series of treatment wetlands.

In the Arboretum, an existing paved drainage channel would be removed and replaced with a widened channel with stone riffles to slow runoff and encourage infiltration into the soil. The design avoided the large trees to ensure there would be no damage to their roots. New wetland plantings would enhance the Arboretum’s collection and display. A 25 foot diameter cistern, partially above and partially below ground would serve as additional storage for irrigation water and would be integrated into the path system. Paths, drainage channel and pond would demonstrate the integration of arboretum display with sustainable stormwater management.

Surface Ponds for Stormwater treatment and re-use

A pond is proposed on the lawn south of McIver Dormitory. New stormwater infrastructure will intercept the run-off from the Arboretum and the roof drains of McIver and carry this water to the pond. This pond is designed with both a hard and a soft edge to include a wetland as well as a sitting terrace and direct access to the water. The soft edge should be planted with wetland plants at several water depths. These plants demonstrate the relationship of plant to water depth following a gradient that begins with aquatics such as water lilies, emergent species such as sedges, rushes and finishes with lowland trees and shrubs at the pond edge. The pond edge should be constructed with pockets to provide habitat for fish, frogs, etc. The pond edge can incorporate water features and provide additional length to accommodate stormwater overflow. Secondary ponds can also be added to this design.

Figure 5-29 McIVER LAWN COULD ACCOMMODATE TREATMENT WETLANDS

Pond Section

For a “balanced life pond”, pond depth should be 4 to 6 feet deep. The pond bottom should be constructed in a series of layers— geotextile fabric under 6 inches of clean gravel, a 45 mil polypropylene liner over 2 inches of sand liner padding, over a layer of large stones, topped with 2 inches of gravel. Pond mechanical and plumbing would include: sumps, pumps, pipes and a concrete vault.

Constructed Treatment Wetlands

In the Coker Arboretum a series of constructed wetlands to hold sediment and filter pollutants are proposed as part of the stormwater system. The existing channelized swale would be removed in some sections and a series of small wetlands created, with check dams to decrease the velocity and peak flows of runoff. Wetland vegetation would filter sediments and take up nutrients from the runoff, as well as provide arboretum displays.

Figure 5-30 CONCEPTUAL PLAN AND SECTION FOR TREATMENT WETLANDS AND POND IN THE COKER ARBORETUM

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CASE STUDY 6 | Ambulatory Care Center Storage and Reuse

A planned addition to the Ambulatory Care Center is located in sub-watershed MO-1 (a direct tributary of Morgan Creek) that drains from the southwest corner of the campus. This portion of the campus contains 45% impervious surface and with the new building this percentage will increase.

In order to mitigate the greater volume of stormwater, as required by Town Ordinance for this proposed addition, a corresponding reduction in runoff volume must be provided. A system was developed for the Ambulatory Care Center that captures and detains but does not infiltrate 6,700 cubic feet of runoff. However, water must be continuously removed from this system or there will be no volume mitigation.

The Ambulatory Care Center parking lot is located in sub–watershed MO-1. This parking lot is in high demand and provides over 217 parking spaces for the facility. The initial proposal was to retrofit the islands in the existing parking lot to serve as landscape infiltration structures—to convey, store, and infiltrate runoff from the road and the parking lot. As stormwater from parking areas and adjacent roads is more prone to concentrate sediments, such a retrofit would also have provided water quality improvement by filtering out NPS pollutants and coarse sediments.

In the initial scheme, four of the existing small islands would be consolidated and expanded, while three of the existing islands would be removed, resulting in the loss of only one parking space. Construction of infiltration beds beneath the parking islands would involve excavating several feet of soil below the existing planting island and replacing it with clean, washed aggregate beneath a layer of soil, with approximately a 10’ x 20’ x 2.5’ bed of stone and a foot of planting soil. Geotextile fabric lining the walls of the bed would prevent clogging sediments from filling the voids between the stones and impermeable synthetic liners along the perimeter would prevent water from migrating under the asphalt.

Figure 5-31 INFILTRATION IN PLANTED ISLANDS AT THE AMBULATORY CARE CENTERFigure 5-32 CONCEPTUAL PLAN FOR STORMWATER MANAGEMENT, AMBULATORY CARE CENTER

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Slotted curbs would replace the existing continuous curbs to allow run-off to be evenly dispersed between the plantings of the islands. A curbless design would function in the same way. Check dams are recommended at regular intervals to slow the run-off and allow for infiltration. These check dams would be constructed of coir logs and planted with shrubs. Infiltration would be enhanced by incorporating french drains lined with filter fabric into the design of the planting islands. The system would also provide for potential overflow to the storm system (Figure 5-33, Figure 5-34).

Native riparian species are suited to both wet and dry conditions typical of these island swales and would tolerate periods of inundation as well as very dry conditions. Sediment deposition will occur over time and periodic maintenance would be required to remove accumulated sediments. Since all the adjacent forest was removed to install the pipes that provide storage for this BMP and since trees are the most effective BMP, it is recommended that the forest be replanted on the slopes.

CASE STUDY 7 | School of Public Health

An important level of protection from stormwater runoff can be provided for a cleared woodland slope by creating a low earth berm with Infiltration Trenches. The berm reduces the frequency and velocity of over-slope water movement and provides limited stormwater infiltration. It is critical that the berm be placed at right angles to the slope and filled with 3-4 inch stones to create a linear soak pit. Sediment must be controlled with filter fabric or the trench will silt in rapidly. Soil from the trench should be used to create the berm, separating the topsoil from the subsoil and replacing the topsoil on the top of the berm. The berm should be planted to prevent erosion, increase the roughness of the ground and slow movement of any water not retained.

This BMP is proposed for the southern perimeter of the School of Public Health—currently a Cleared Woodland cover type, with many areas of bare, eroded soil. This is a low cost, effective technique that could have wider application on the many wooded slopes of the UNC-Chapel Hill campus.

Figure 5-34 SECTION AT EDGE OF WOODED SLOPE, SCHOOL OF PUBLIC HEALTH

Figure 5-35 CONCEPTUAL PLAN SHOWING INFILTRATION TRENCHES AT EDGE OF WOODED SLOPE, SCHOOL OF PUBLIC HEALTH

Figure 5-33 PROPOSED SLOTTED CURBS REPLACE EXISTING CONTINUOUS CURBS. PROPOSED PARKING LOT ISLANDS WITH INFILTRATION BEDS.

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5.6 SUMMARY

This Stormwater Management Plan is a small but critical portion of an ambitious UNC-Chapel Hill program to become a “green campus” and a model for other universities around the country. A remarkable amount of the stormwater management program has already been put in place including:

• Acceptance by the University administration• Development of design and construction guidelines• Close coordination with Town officials on the Town of Chapel Hill Zoning Ordinance for

New Development.• Illicit discharge elimination• Public stormwater education programs• Street sweeping• Incorporation of the many BMPs recommended here in new campus projects.

With the present Stormwater Management Plan and its list of proposed BMPs, the University will be able to comply with the town of Chapel Hill 01-4 Zoning Ordinance. The volume of stormwater that can be reduced with the projects presently proposed by the University will provide substantially more volume reduction than the 139,000 cubic feet required under the Town Ordinance. Even this volume reduction is only a small portion of the potential estimated for the full mix of BMPs shown in Table 5-2.

However, despite these remarkable and innovative efforts, the burden of existing conditions still remains. With over 70% impervious surfaces in the most highly developed campus sub-watersheds, especially ME-1 and ME-2, problems of runoff generated during heavy rainfalls will still not be significantly reduced.

What is needed in the future is a greater investment in comprehensive Stormwater Management, particularly in the uplands where run-off originates and where no projects may currently be planned. Further study is also needed, particularly in sub-watersheds ME-1 and ME-2, to address existing conditions and impacts, as well as the increased impervious surfaces created by building projects to be realized in the Eight-Year Development Plan. It is hoped that the recommendations of this Stormwater Management Plan will continue to evolve as they are monitored and tested in these projects.

This innovative undertaking is a work in progress in which the process is one of learning by doing. In order to succeed, the guiding principles of this report should be re-iterated: 1. It is best to manage stormwater where the problem is generated. This approach prevents exacerbation of downstream problems. 2. A number of Stormwater management options–large and small–distributed throughout a drainage area is inherently better than a single large solution, which if it fails, will have far larger consequences.

As long as these principles are followed, this evolving project should continue to grow and flourish.

UNC-Chapel Hill Stormwater Management ProgramTable 2-2. Water Balance Model Values for Existing and Future Land Use Conditions

Lead Copper Zinc (CN) (TSS) (TP) (NO3 & NO2) (Pb) (Cu) (Zn)

Impervious SurfacesBuildings* 98 1 0.1 0.23 0.4 0.004 0.024 0.193Roads/Parking 98 180 0.6 0.55 6 0.015 0.047 0.111Pedestrian Pathways & Recreation** 98 80 0.3 0.33 0.27 0.012 0.014 0.027Pervious & Semi-pervious SurfacesForest 55 53 0.2 0.17 0 0.002 0.008 0.01Managed Woodland 65 53 0.2 0.17 0 0.002 0.008 0.01Fertilized Planting Area 70 200 1.3 0.6 0 0.007 0.01 0.013Rough Grass 74 104 1.7 0.73 0 0.007 0.01 0.013Lawn 79 133 2 0.87 0 0.007 0.01 0.013Grass Playfield 79 160 2.5 1.13 0 0.007 0.01 0.013*Includes existing and proposed buildings as well as roof gardens/plazas.**Includes pathways, recreation areas, artificial turf playfields, and sand courts.

Sources: (1) U.S. EPA (Results of the Nationwide Urban Runoff Program - 1983) (2) FHWA (Pollutant Loadings and Impacts from Highway Stormwater Runoff - 1990) (3) Characterization of Nonpoint Sources and Loadings to Corpus Christi Bay (1996)(4) Philadelphia Water Department Technical Memorandum No. 3 (2000)(5) Technical Note #105 from Watershed Protection Techniques (1997)(6) Center for Watershed Protection (Design of Stormwater Filtering Systems - 1995)

Curve NumberLand Use Categories

Total Suspended Solids

Total Phosphorus

Event Mean Concentrations (mg/L)Nitrate &

NitritePetroleum

HydrocarbonsHeavy Metals

UNC-Chapel Hill Stormwater Management ProgramWater Balance Model Values for Landscape Plan Conditions

Lead Copper Zinc (CN) (TSS) (TP) (NO3 & NO2) (Pb) (Cu) (Zn)

Impervious SurfacesBuildings* 98 1 0.1 0.23 0.4 0.004 0.024 0.193Roads/Parking 98 180 0.6 0.55 6 0.015 0.047 0.111Pedestrian Pathways & Recreation** 98 80 0.3 0.33 0.27 0.012 0.014 0.027Pervious & Semi-pervious SurfacesForest 55 53 0.2 0.17 0 0.002 0.008 0.01Managed Woodland 65 53 0.2 0.17 0 0.002 0.008 0.01

Fertilized Planting Area 70 200 1.3 0.6 0 0.007 0.01 0.013Rough Grass 74 104 1.7 0.73 0 0.007 0.01 0.013Lawn 79 133 2 0.87 0 0.007 0.01 0.013Grass Playfield 79 160 2.5 1.13 0 0.007 0.01 0.013*Includes existing and proposed buildings as well as roof gardens/plazas.**Includes pathways, recreation areas, artificial turf playfields, and sand courts.

Sources: (1) U.S. EPA (Results of the Nationwide Urban Runoff Program - 1983) (2) FHWA (Pollutant Loadings and Impacts from Highway Stormwater Runoff - 1990) (3) Characterization of Nonpoint Sources and Loadings to Corpus Christi Bay (1996)(4) Philadelphia Water Department Technical Memorandum No. 3 (2000)(5) Technical Note #105 from Watershed Protection Techniques (1997)(6) Center for Watershed Protection (Design of Stormwater Filtering Systems - 1995)

0.010.27 0 0.002 0.008Un-fertilized Planting Area, Old Field Meadow, Rain Garden

70 200 0.4

Event Mean Concentrations (mg/L)

Land Use CategoriesCurve

NumberTotal Suspended

SolidsTotal

Phosphorus Nitrate &

NitritePetroleum

HydrocarbonsHeavy Metals

UNC-Chapel Hill Stormwater Management ProgramLand Cover Area Comparison

Existing 9.5 11.2 12.3 75.0 1.1 0.0 10.1 0.1 16.8 0.0 136.0 24.26%8-Yr Development 9.7 11.2 12.2 75.0 1.1 0.0 9.5 0.1 17.0 0.0 136.0 24.34%Landscape Plan 9.7 11.2 12.2 76.1 0.0 6.0 8.7 0.0 13.5 0.0 136.0 24.34%





Land Use Area SummaryLand Use Change between Existing and 8-yr Development

Area (acre)Change in Impervious Area 6.4Increase in Buildings 23.8Decrease in Roads -19.7Increase in Lawns 28.1Decrease in Forest -21.2

TotalPercent

ImperviousLand Use Condition

Fertilized Planting

Area

Un-Fertilized Planting Area, Old Meadow

Rain GardenManaged WoodlandForest

Pedestrian Pathways & Recreation

Rough Grass Lawn

Grass Playfield

AREA (Acres)

Roads/ParkingBuildings

Meeting of the Waters Creek

Morgan Creek

Watershed

Battle Creek

Bolin Creek

Chapel Creek

Rainfall (inches/24 hours)1-yr 2-yr 5-yr 10-yr 100-yr2.8 3.6 4.7 5.38 8.0

Land Cover Land Uses Included CN S Ia (in)Runoff (inches/24 hours)

Impervious Roofs, pavements, roads 98 0.20 0.04 2.57 3.37 4.46 5.14 7.76

Pervious Forest 55 8.18 1.64 0.14 0.38 0.83 1.18 2.78Managed Woodland 65 5.38 1.08 0.42 0.81 1.46 1.91 3.89Planting Areas 70 4.29 0.86 0.61 1.07 1.82 2.32 4.46Rough Grass 74 3.51 0.70 0.78 1.31 2.13 2.67 4.93Lawns 79 2.66 0.53 1.04 1.64 2.55 3.13 5.51Grass Playfields 79 2.66 0.53 1.04 1.64 2.55 3.13 5.51

UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINSCS Curve Numbers and Runoff Volumes

(Based on all soil series of Hydrologic Soil Group C except Woodland)

UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINRunoff Coefficients and Event Mean Concentrations (EMCs)

Land Cover ForestManaged Woodland

Fertilized Planting Area Rough Grass Lawn Grass Playfield Building

Road/ Parking

Pedestrian Pathway & Rec. Area*

Runoff Coeff. (Annual) 0.1 0.15 0.25 0.3 0.35 0.35 0.95 0.95 0.95Runoff Coeff. (1" Storm) 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80

EMCs (mg/L)TSS 40 40 150 78 100 120 1 135 60

NO3 + NO2 (as N) 0.3 0.3 0.9 1.1 1.3 1.70 0.34 0.83 0.5TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19

COD 40 40 53 53 60 65 1 85 50Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.003 0.011 0.009

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.290 0.167 0.04

Oil & Grease 0 0 0 0 0 0 0.6 9 0.4

* Includes impervious recreational areas, artificial turf fields, and sand courts.

(1) U.S. EPA (Results of the Nationwide Urban Runoff Program - 1983) (2) FHWA (Pollutant Loadings and Impacts from Highway Stormwater Runoff - 1990) (3) Characterization of Nonpoint Sources and Loadings to Corpus Christi Bay (1996)(4) Philadelphia Water Department Technical Memorandum No. 3 (2000)(5) Technical Note #105 from Watershed Protection Techniques (1997)(6) Center for Watershed Protection (Design of Stormwater Filtering Systems - 1995)

Pervious & Semipervious Impervious

UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINSub-Basin: Battle Creek (BA)Land Cover: EXISTING 8-YR DEV.Loading: ANNUAL 1" STORM 2-YR STORM


Fertilized Planting Area

Rough Grass

Lawn Grass Playfield BuildingRoad/

Parking


Water

TOTAL**

Area (ac) 75.00 1.15 9.67 0.10 16.86 0.00 9.56 11.29 12.32 136.0Runoff Coefficient 0.1 0.15 0.25 0.3 0.35 0.35 0.95 0.95 0.95 0.35Rain & Irrigation (in) 46.2 46.2 49.4 46.2 51.9 70.2 46.2 46.2 46.2 47.1Runoff Volume (ac-in) 346 8 125 2 327 0 431 508 622 2369EMCs (mg/L)

TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---

Oil & Grease 0 0 0 0 0 0 0.6 9 0.4 ---Loadings (lb/yr)

TSS 3132.4 72.0 4049.4 24.4 6927.7 0.0 94.8 15118.3 7332.2 36751.2NO3 + NO2 19.6 0.5 24.3 0.3 90.1 0.0 32.2 92.9 61.1 321.0

TP 11.4 0.3 27.0 0.4 103.9 0.0 7.6 48.2 23.2 221.9COD 3132.4 72.0 1430.8 16.6 4156.6 0.0 94.8 9518.9 6110.2 24532.3Lead 0.1 0.0 0.1 0.0 0.3 0.0 0.3 1.2 1.1 3.2

Copper 0.6 0.0 0.3 0.0 0.7 0.0 2.3 5.3 1.7 10.9Zinc 1.2 0.0 0.5 0.0 1.4 0.0 27.5 18.7 4.9 54.2

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 56.9 1007.9 48.9 1113.7

* Includes impervious recreational areas, artificial turf fields, and sand courts.** Includes surface water that is not included in Land Cover categories.



Land Cover Forest Managed Woodland


Rough Grass

Lawn Grass Playfield Building Road/ Parking


Water

TOTAL**

Area (ac) 75.0 1.2 9.7 0.1 16.9 0.0 9.6 11.3 12.3 136.0Curver Number (CN) 55 65 70 74 79 79 98 98 98 70Runoff (in) 0.38 0.81 1.07 1.31 1.64 1.64 3.37 3.37 3.37 1.32Runoff Volume (ac-in) 28.5 0.9 10.8 0.2 29.6 0.0 33.1 39.0 47.7 190EMCs (mg/L)***

TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---

Oil & Grease 0 0 0 0 0 0 0.4 6.0 0.27 ---Loadings (lb/storm)

TSS 343.6 11.2 467.8 3.1 835.3 0.0 9.7 1546.0 749.8 3966.4NO3 + NO2 1.1 0.0 1.4 0.0 5.4 0.0 1.6 4.8 3.1 17.5

TP 1.2 0.0 3.1 0.0 12.5 0.0 0.8 4.9 2.4 25.1COD 343.6 11.2 165.3 2.1 501.2 0.0 9.7 973.4 624.8 2631.2Lead 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.3

Copper 0.1 0.0 0.0 0.0 0.1 0.0 0.2 0.4 0.1 0.8Zinc 0.1 0.0 0.0 0.0 0.1 0.0 1.4 1.0 0.2 2.8

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 2.9 51.5 2.5 56.9


*** Annual EMC Adjustment for 2-Yr StormParticulate Pollutants 1.33 (TSS, TP, Pb, COD)Soluble Pollutants 0.67 (N, Zn, O+G)





Rough Grass



Water

TOTAL**

Area (ac) 75.0 1.2 9.7 0.1 16.9 0.0 9.6 11.3 12.3 136.0Runoff Coefficient 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80 ---Runoff (in) 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80 0.23Runoff Volume (ac-in) 0.0 0.0 1.5 0.0 3.8 0.0 7.9 9.3 11.3 34EMCs (mg/L)***

TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---

Oil & Grease --- --- 0 0 0 0.00 0.80 12 0.53 ---Loadings (lb/storm)

TSS --- --- 34 0 57 0 1.2 189 103 384.4NO3 + NO2 --- --- 0.4 0.0 1.5 0.0 0.8 2.3 1.7 6.7

TP --- --- 0.2 0.0 0.9 0.0 0.1 0.6 0.3 2.1COD --- --- 12 0 34 0 1.2 119 86 252.3Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.2Zinc --- --- 0.0 0.0 0.0 0.0 0.7 0.5 0.1 1.3

Oil & Grease --- --- 0 0 0 0 1.4 25 1.4 28.0


*** Annual EMC Adjustment for 1" StormParticulate Pollutants 0.67 (TSS, TP, Pb, COD)Soluble Pollutants 1.33 (N, Zn, O+G)


UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINSub-Basin: Bolin Creek (BO)Land Cover: EXISTING 8-YR DEV.Loading: ANNUAL 1" STORM 2-YR STORM



Rough Grass



Water

TOTAL**


TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 0.0 0.0 1098.6 0.0 5077.9 0.0 47.6 5356.3 2916.2 14496.7NO3 + NO2 0.0 0.0 6.6 0.0 66.0 0.0 16.2 32.9 24.3 146.0

TP 0.0 0.0 7.3 0.0 76.2 0.0 3.8 17.1 9.2 113.6COD 0.0 0.0 388.2 0.0 3046.8 0.0 47.6 3372.5 2430.2 9285.2Lead 0.0 0.0 0.0 0.0 0.3 0.0 0.1 0.4 0.4 1.3

Copper 0.0 0.0 0.1 0.0 0.5 0.0 1.1 1.9 0.7 4.3Zinc 0.0 0.0 0.1 0.0 1.0 0.0 13.8 6.6 1.9 23.5

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 28.6 357.1 19.4 405.1






Rough Grass



Water

TOTAL**

Area (ac) 0.0 0.0 2.6 0.0 11.0 0.0 4.8 4.0 4.9 27.4Runoff Coefficient 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80 ---Runoff (in) 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80 0.50Runoff Volume (ac-in) 0.0 0.0 0.5 0.0 2.4 0.0 4.4 4.3 4.3 16EMCs (mg/L)*

TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 10 0 37 0 0.7 89 39 175.5NO3 + NO2 --- --- 0.1 0.0 1.0 0.0 0.4 1.1 0.7 3.3

TP --- --- 0.1 0.0 0.6 0.0 0.1 0.3 0.1 1.1COD --- --- 4 0 22 0 0.7 56 33 114.8Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1Zinc --- --- 0.0 0.0 0.0 0.0 0.4 0.2 0.1 0.7

Oil & Grease --- --- 0 0 0 0 0.8 12 0.5 13.1







Rough Grass



Water

TOTAL**

Area (ac) 0.0 0.0 2.6 0.0 11.0 0.0 4.8 4.0 4.9 27.4Curver Number (CN) 55 65 70 74 79 79 98 98 98 87Runoff (in) 0.38 0.81 1.07 1.31 1.64 1.64 3.37 3.37 3.37 2.44Runoff Volume (ac-in) 0.0 0.0 3.3 0.0 19.0 0.0 18.4 18.3 18.2 77EMCs (mg/L)*

TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 0.0 0.0 125.8 0.0 544.9 0.0 4.9 547.7 298.2 1802.9NO3 + NO2 0.0 0.0 0.4 0.0 3.5 0.0 0.8 1.7 1.2 8.8

TP 0.0 0.0 0.8 0.0 8.2 0.0 0.4 1.7 0.9 13.5COD 0.0 0.0 44.4 0.0 327.0 0.0 4.9 344.9 248.5 1146.6Lead 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2

Copper 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 0.4Zinc 0.0 0.0 0.0 0.0 0.1 0.0 0.7 0.3 0.1 1.4

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 1.5 18.3 1.0 27.6




UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINSub-Basin: Chapel Creek (CH)Land Cover: EXISTING 8-YR DEV.Loading: ANNUAL 1" STORM 2-YR STORM



Rough Grass



Water

TOTAL**


TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 2018.0 71.4 90.1 0.0 8129.5 0.0 4.0 5624.2 1660.5 17597.5NO3 + NO2 12.6 0.4 0.5 0.0 105.7 0.0 1.3 34.6 13.8 169.0

TP 7.3 0.3 0.6 0.0 121.9 0.0 0.3 17.9 5.3 153.6COD 2018.0 71.4 31.8 0.0 4877.7 0.0 4.0 3541.1 1383.7 11927.7Lead 0.1 0.0 0.0 0.0 0.4 0.0 0.0 0.5 0.2 1.2

Copper 0.4 0.0 0.0 0.0 0.8 0.0 0.1 2.0 0.4 3.7Zinc 0.8 0.0 0.0 0.0 1.6 0.0 1.2 7.0 1.1 11.6

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 2.4 374.9 11.1 388.4






Rough Grass



Water

TOTAL**


TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 1 0 69 0 0.0 67 19 155.1NO3 + NO2 --- --- 0.0 0.0 1.8 0.0 0.0 0.8 0.3 2.9

TP --- --- 0.0 0.0 1.0 0.0 0.0 0.2 0.1 1.3COD --- --- 0 0 41 0 0.0 42 16 99.3Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1Zinc --- --- 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.2

Oil & Grease --- --- 0 0 0 0 0.0 9 0.3 9.1







Rough Grass



Water

TOTAL**


TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 219.9 11.1 11.1 0.0 1089.9 0.0 0.4 575.1 169.8 2037.2NO3 + NO2 0.7 0.0 0.0 0.0 7.1 0.0 0.1 1.8 0.7 10.2

TP 0.8 0.0 0.1 0.0 16.3 0.0 0.0 1.8 0.5 19.4COD 219.9 11.1 3.9 0.0 653.9 0.0 0.4 362.1 141.5 1365.5Lead 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.1

Copper 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.2 0.0 0.3Zinc 0.0 0.0 0.0 0.0 0.1 0.0 0.1 0.4 0.1 0.6

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 0.1 19.2 0.6 19.2




UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINSub-Basin: Meeting of the Waters (ME)Land Cover: EXISTING 8-YR DEV.Loading: ANNUAL 1" STORM 2-YR STORM



Rough Grass



Water

TOTAL**


TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 4068.9 968.5 11456.0 1378.4 26657.5 7929.4 783.6 116634.2 29281.3 199157.8NO3 + NO2 25.4 6.1 68.7 19.4 346.5 112.3 266.4 717.1 244.0 1806.1

TP 14.7 3.5 76.4 22.1 399.9 125.5 62.7 371.5 92.7 1169.0COD 4068.9 968.5 4047.8 936.6 15994.5 4295.1 783.6 73436.4 24401.1 128932.4Lead 0.2 0.0 0.4 0.1 1.3 0.3 2.1 9.5 4.4 18.3

Copper 0.8 0.2 0.8 0.2 2.7 0.7 18.8 40.6 6.8 71.5Zinc 1.5 0.4 1.5 0.4 5.3 1.3 227.2 144.3 19.5 401.5

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 470.2 7775.6 195.2 8441.0






Rough Grass



Water

TOTAL**


TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 92 12 216 45 9.5 1421 356 2152.3NO3 + NO2 --- --- 1.1 0.3 5.6 1.3 6.5 17.5 5.9 38.2

TP --- --- 0.6 0.2 3.2 0.7 0.8 4.5 1.1 11.2COD --- --- 33 8 129 25 9.5 895 297 1396.0Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.2

Copper --- --- 0.0 0.0 0.0 0.0 0.3 0.7 0.1 1.3Zinc --- --- 0.0 0.0 0.1 0.0 5.5 3.5 0.5 9.7

Oil & Grease --- --- 0 0 0 0 11.5 189 4.8 205.6







Rough Grass



Water

TOTAL**


TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 443.9 145.5 1316.0 172.3 3368.8 707.4 80.1 11927.1 2994.3 21209.3NO3 + NO2 1.4 0.5 3.9 1.2 21.9 5.0 13.6 36.7 12.5 96.9

TP 1.6 0.5 8.8 2.8 50.5 11.2 6.4 38.0 9.5 129.7COD 443.9 145.5 465.0 117.1 2021.3 383.2 80.1 7509.7 2495.3 13695.1Lead 0.0 0.0 0.0 0.0 0.2 0.0 0.2 1.0 0.4 1.9

Copper 0.1 0.0 0.1 0.0 0.3 0.0 1.4 3.1 0.5 5.6Zinc 0.1 0.0 0.1 0.0 0.3 0.1 11.6 7.4 1.0 20.7

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 24.0 397.6 10.0 432.7




UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINSub-Basin: Morgan Creek (MO)Land Cover: EXISTING 8-YR DEV.Loading: ANNUAL 1" STORM 2-YR STORM



Rough Grass



Water

TOTAL**


TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 413.5 479.9 1247.5 334.5 3036.1 0.0 78.0 19912.2 1803.3 27305.0NO3 + NO2 2.6 3.0 7.5 4.7 39.5 0.0 26.5 122.4 15.0 221.2

TP 1.5 1.7 8.3 5.4 45.5 0.0 6.2 63.4 5.7 137.8COD 413.5 479.9 440.8 227.3 1821.6 0.0 78.0 12537.3 1502.7 17501.2Lead 0.0 0.0 0.0 0.0 0.2 0.0 0.2 1.6 0.3 2.4

Copper 0.1 0.1 0.1 0.0 0.3 0.0 1.9 6.9 0.4 9.8Zinc 0.2 0.2 0.2 0.1 0.6 0.0 22.6 24.6 1.2 49.6

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 46.8 1327.5 12.0 1386.3






Rough Grass



Water

TOTAL**


TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 8 3 22 0 0.8 211 19 263.2NO3 + NO2 --- --- 0.1 0.1 0.6 0.0 0.6 2.6 0.3 4.2

TP --- --- 0.1 0.0 0.3 0.0 0.1 0.7 0.1 1.2COD --- --- 3 2 13 0 0.8 133 16 167.1Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.2Zinc --- --- 0.0 0.0 0.0 0.0 0.5 0.5 0.0 1.0

Oil & Grease --- --- 0 0 0 0 1.0 28 0.3 29.3







Rough Grass



Water

TOTAL**


TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 45.4 72.8 150.0 40.0 379.5 0.0 8.0 2036.2 184.4 2554.5NO3 + NO2 0.1 0.2 0.4 0.3 2.5 0.0 1.4 6.3 0.8 10.5

TP 0.2 0.3 1.0 0.6 5.7 0.0 0.6 6.5 0.6 13.7COD 45.4 72.8 53.0 27.2 227.7 0.0 8.0 1282.1 153.7 1644.9Lead 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.2

Copper 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.5 0.0 0.7Zinc 0.0 0.0 0.0 0.0 0.0 0.0 1.2 1.3 0.1 2.2

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 2.4 67.9 0.6 61.7




Rainfall (inches/24 hours)1-yr 2-yr 5-yr 10-yr 100-yr2.8 3.6 4.7 5.38 8.0

Land Cover Land Uses Included CN S Ia (in)Runoff (inches/24 hours)

Impervious Roofs, pavements, roads 98 0.20 0.04 2.57 3.37 4.46 5.14 7.76

Pervious Forest 55 8.18 1.64 0.14 0.38 0.83 1.18 2.78Managed Woodland 65 5.38 1.08 0.42 0.81 1.46 1.91 3.89Planting Areas 70 4.29 0.86 0.61 1.07 1.82 2.32 4.46Rough Grass 74 3.51 0.70 0.78 1.31 2.13 2.67 4.93Lawns 79 2.66 0.53 1.04 1.64 2.55 3.13 5.51Grass Playfields 79 2.66 0.53 1.04 1.64 2.55 3.13 5.51

UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINSCS Curve Numbers and Runoff Volumes

(Based on all soil series of Hydrologic Soil Group C except Woodland)

UNC-CHAPEL HILL, NON-POINT SOURCE LOADING ANALYSIS BY SUB-BASINRunoff Coefficients and Event Mean Concentrations (EMCs)


Fertilized Planting Area Rough Grass Lawn Grass Playfield Building

Road/ Parking


Runoff Coeff. (Annual) 0.1 0.15 0.25 0.3 0.35 0.35 0.95 0.95 0.95Runoff Coeff. (1" Storm) 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80

EMCs (mg/L)TSS 40 40 150 78 100 120 1 135 60

NO3 + NO2 (as N) 0.3 0.3 0.9 1.1 1.3 1.70 0.34 0.83 0.5TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19

COD 40 40 53 53 60 65 1 85 50Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.003 0.011 0.009

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.290 0.167 0.04

Oil & Grease 0 0 0 0 0 0 0.6 9 0.4

* Includes impervious recreational areas, artificial turf fields, and sand courts.

(1) U.S. EPA (Results of the Nationwide Urban Runoff Program - 1983) (2) FHWA (Pollutant Loadings and Impacts from Highway Stormwater Runoff - 1990) (3) Characterization of Nonpoint Sources and Loadings to Corpus Christi Bay (1996)(4) Philadelphia Water Department Technical Memorandum No. 3 (2000)(5) Technical Note #105 from Watershed Protection Techniques (1997)(6) Center for Watershed Protection (Design of Stormwater Filtering Systems - 1995)





Rough Grass



Water

TOTAL**

Area (ac) 74.96 1.15 9.59 0.1 16.87 0.00 9.72 11.24 12.28 136Runoff Coefficient 0.1 0.15 0.25 0.3 0.35 0.35 0.95 0.95 0.95 0.35Rain & Irrigation (in) 46.2 46.2 49.4 46.2 51.9 70.2 46.2 46.2 46.2 47.1Runoff Volume (ac-in) 346 8 125 2 327 0 431 508 622 2369EMCs (mg/L)

TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 3130.7 72.0 4015.9 24.4 6931.8 0.0 96.4 15051.3 7308.4 36631.0NO3 + NO2 19.6 0.5 24.1 0.3 90.1 0.0 32.8 92.5 60.9 320.8

TP 11.3 0.3 26.8 0.4 104.0 0.0 7.7 47.9 23.1 221.5COD 3130.7 72.0 1418.9 16.6 4159.1 0.0 96.4 9476.7 6090.4 24460.9Lead 0.1 0.0 0.1 0.0 0.3 0.0 0.3 1.2 1.1 3.2

Copper 0.6 0.0 0.3 0.0 0.7 0.0 2.3 5.2 1.7 10.9Zinc 1.2 0.0 0.5 0.0 1.4 0.0 28.0 18.6 4.9 54.6

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 57.8 1003.4 48.7 1110.0






Rough Grass



Water

TOTAL**

Area (ac) 75.0 1.2 9.6 0.1 16.9 0.0 9.7 11.2 12.3 136Runoff Coefficient 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80 ---Runoff (in) 0.00 0.00 0.15 0.18 0.21 0.21 0.80 0.80 0.80 0.23Runoff Volume (ac-in) 0.0 0.0 1.5 0.0 3.8 0.0 7.9 9.3 11.3 34EMCs (mg/L)***

TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 34 0 57 0 1.2 189 103 384.4NO3 + NO2 --- --- 0.4 0.0 1.5 0.0 0.8 2.3 1.7 6.7

TP --- --- 0.2 0.0 0.9 0.0 0.1 0.6 0.3 2.1COD --- --- 12 0 34 0 1.2 119 86 252.3Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.2Zinc --- --- 0.0 0.0 0.0 0.0 0.7 0.5 0.1 1.3

Oil & Grease --- --- 0 0 0 0 1.4 25 1.4 28.0







Rough Grass



Water

TOTAL**

Area (ac) 75.0 1.2 9.6 0.1 16.9 0.0 9.7 11.2 12.3 136Curver Number (CN) 55 65 70 74 79 79 98 98 98 70Runoff (in) 0.38 0.81 1.07 1.31 1.64 1.64 3.37 3.37 3.37 1.32Runoff Volume (ac-in) 28.5 0.9 10.8 0.2 29.6 0.0 33.1 39.0 47.7 190EMCs (mg/L)***

TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 343.4 11.2 464.0 3.1 835.8 0.0 9.9 1539.2 747.4 3953.7NO3 + NO2 1.1 0.0 1.4 0.0 5.4 0.0 1.7 4.7 3.1 17.5

TP 1.2 0.0 3.1 0.0 12.5 0.0 0.8 4.9 2.4 25.0COD 343.4 11.2 163.9 2.1 501.5 0.0 9.9 969.1 622.8 2623.8Lead 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.3

Copper 0.1 0.0 0.0 0.0 0.1 0.0 0.2 0.4 0.1 0.8Zinc 0.1 0.0 0.0 0.0 0.1 0.0 1.4 1.0 0.2 2.8

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 3.0 51.3 2.5 56.8







Rough Grass



Water

TOTAL**


TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 0.0 0.0 781.7 0.0 5539.6 0.0 49.6 4552.9 3451.9 14375.6NO3 + NO2 0.0 0.0 4.7 0.0 72.0 0.0 16.9 28.0 28.8 150.3

TP 0.0 0.0 5.2 0.0 83.1 0.0 4.0 14.5 10.9 117.7COD 0.0 0.0 276.2 0.0 3323.7 0.0 49.6 2866.6 2876.6 9392.7Lead 0.0 0.0 0.0 0.0 0.3 0.0 0.1 0.4 0.5 1.3

Copper 0.0 0.0 0.1 0.0 0.6 0.0 1.2 1.6 0.8 4.2Zinc 0.0 0.0 0.1 0.0 1.1 0.0 14.4 5.6 2.3 23.5

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 29.8 303.5 23.0 356.3






Rough Grass



Water

TOTAL**


TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 10 0 37 0 0.7 89 39 175.5NO3 + NO2 --- --- 0.1 0.0 1.0 0.0 0.4 1.1 0.7 3.3

TP --- --- 0.1 0.0 0.6 0.0 0.1 0.3 0.1 1.1COD --- --- 4 0 22 0 0.7 56 33 114.8Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1Zinc --- --- 0.0 0.0 0.0 0.0 0.4 0.2 0.1 0.7

Oil & Grease --- --- 0 0 0 0 0.8 12 0.5 13.1







Rough Grass



Water

TOTAL**


TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 0.0 0.0 89.5 0.0 594.5 0.0 5.1 465.6 353.0 1802.9NO3 + NO2 0.0 0.0 0.3 0.0 3.9 0.0 0.9 1.4 1.5 8.8

TP 0.0 0.0 0.6 0.0 8.9 0.0 0.4 1.5 1.1 13.5COD 0.0 0.0 31.6 0.0 356.7 0.0 5.1 293.1 294.2 1146.6Lead 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.2

Copper 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.1 0.4Zinc 0.0 0.0 0.0 0.0 0.1 0.0 0.7 0.3 0.1 1.4

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 1.5 15.5 1.2 27.6







Rough Grass



Water

TOTAL**

Area (ac) 48.0 1.13 0.23 0 22.0 0.00 0.39 4.27 2.79 79.2Runoff Coefficient 0.1 0.15 0.25 0.3 0.35 0.35 0.95 0.95 0.95 0.25Rain & Irrigation (in) 46.5 46.2 46.2 46.2 46.7 70.2 46.2 46.2 46.2 46.3Runoff Volume (ac-in) 224 6 2 0 355 0 7 179 115 888EMCs (mg/L)

TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 2018.0 70.8 90.1 0.0 8118.4 0.0 3.9 5717.9 1660.5 17679.4NO3 + NO2 12.6 0.4 0.5 0.0 105.5 0.0 1.3 35.2 13.8 169.4

TP 7.3 0.3 0.6 0.0 121.8 0.0 0.3 18.2 5.3 153.7COD 2018.0 70.8 31.8 0.0 4871.0 0.0 3.9 3600.2 1383.7 11979.4Lead 0.1 0.0 0.0 0.0 0.4 0.0 0.0 0.5 0.2 1.2

Copper 0.4 0.0 0.0 0.0 0.8 0.0 0.1 2.0 0.4 3.7Zinc 0.8 0.0 0.0 0.0 1.6 0.0 1.1 7.1 1.1 11.7

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 2.3 381.2 11.1 394.6






Rough Grass



Water

TOTAL**


TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 1 0 69 0 0.0 67 19 155.1NO3 + NO2 --- --- 0.0 0.0 1.8 0.0 0.0 0.8 0.3 2.9

TP --- --- 0.0 0.0 1.0 0.0 0.0 0.2 0.1 1.3COD --- --- 0 0 41 0 0.0 42 16 99.3Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1Zinc --- --- 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.2

Oil & Grease --- --- 0 0 0 0 0.0 9 0.3 9.1







Rough Grass



Water

TOTAL**


TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 219.9 11.0 11.1 0.0 1088.4 0.0 0.4 584.7 169.8 2037.2NO3 + NO2 0.7 0.0 0.0 0.0 7.1 0.0 0.1 1.8 0.7 10.2

TP 0.8 0.0 0.1 0.0 16.3 0.0 0.0 1.9 0.5 19.4COD 219.9 11.0 3.9 0.0 653.0 0.0 0.4 368.2 141.5 1365.5Lead 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.1

Copper 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.2 0.0 0.3Zinc 0.0 0.0 0.0 0.0 0.1 0.0 0.1 0.4 0.1 0.6

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 0.1 19.5 0.6 19.2







Rough Grass



Water

TOTAL**


TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 3237.5 742.5 9097.4 787.6 36379.6 9475.3 987.9 92262.9 30055.0 183025.8NO3 + NO2 20.2 4.6 54.6 11.1 472.9 134.2 335.9 567.2 250.5 1851.3

TP 11.7 2.7 60.6 12.6 545.7 150.0 79.0 293.9 95.2 1251.5COD 3237.5 742.5 3214.4 535.2 21827.8 5132.5 987.9 58091.4 25045.8 118815.1Lead 0.1 0.0 0.3 0.1 1.8 0.4 2.7 7.5 4.5 17.4

Copper 0.6 0.1 0.6 0.1 3.6 0.8 23.7 32.1 7.0 68.8Zinc 1.2 0.3 1.2 0.2 7.3 1.6 286.5 114.1 20.0 432.4

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 592.8 6150.9 200.4 6944.0






Rough Grass



Water

TOTAL**


TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 92 12 216 45 9.5 1421 356 2152.3NO3 + NO2 --- --- 1.1 0.3 5.6 1.3 6.5 17.5 5.9 38.2

TP --- --- 0.6 0.2 3.2 0.7 0.8 4.5 1.1 11.2COD --- --- 33 8 129 25 9.5 895 297 1396.0Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.1 0.1 0.2

Copper --- --- 0.0 0.0 0.0 0.0 0.3 0.7 0.1 1.3Zinc --- --- 0.0 0.0 0.1 0.0 5.5 3.5 0.5 9.7

Oil & Grease --- --- 0 0 0 0 11.5 189 4.8 205.6







Rough Grass



Water

TOTAL**


TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 353.2 111.6 1045.0 98.5 4597.4 845.4 101.0 9434.9 3073.4 21209.3NO3 + NO2 1.1 0.3 3.1 0.7 29.9 6.0 17.2 29.0 12.8 96.9

TP 1.3 0.4 7.0 1.6 69.0 13.4 8.1 30.1 9.7 129.7COD 353.2 111.6 369.2 66.9 2758.4 457.9 101.0 5940.5 2561.2 13695.1Lead 0.0 0.0 0.0 0.0 0.2 0.0 0.3 0.8 0.5 1.9

Copper 0.1 0.0 0.1 0.0 0.3 0.1 1.8 2.5 0.5 5.6Zinc 0.1 0.0 0.1 0.0 0.5 0.1 14.6 5.8 1.0 20.7

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 30.3 314.5 10.2 432.7







Rough Grass



Water

TOTAL**


TSS 40 40 150 78 100 120 1 135 60 ---NO3 + NO2 (as N) 0.25 0.25 0.9 1.1 1.3 1.7 0.34 0.83 0.5 ---

TP 0.145 0.145 1 1.25 1.5 1.9 0.08 0.43 0.19 ---COD 40 40 53 53 60 65 1 85 50 ---Lead 0.0015 0.0015 0.005 0.005 0.005 0.005 0.0027 0.011 0.009 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.015 0.015 0.02 0.02 0.02 0.02 0.29 0.167 0.04 ---


TSS 354.6 308.4 1155.0 110.6 4165.7 0.0 105.1 18466.0 2225.9 26891.3NO3 + NO2 2.2 1.9 6.9 1.6 54.2 0.0 35.7 113.5 18.5 234.6

TP 1.3 1.1 7.7 1.8 62.5 0.0 8.4 58.8 7.0 148.6COD 354.6 308.4 408.1 75.2 2499.4 0.0 105.1 11626.7 1854.9 17232.5Lead 0.0 0.0 0.0 0.0 0.2 0.0 0.3 1.5 0.3 2.4

Copper 0.1 0.1 0.1 0.0 0.4 0.0 2.5 6.4 0.5 10.1Zinc 0.1 0.1 0.2 0.0 0.8 0.0 30.5 22.8 1.5 56.1

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 63.1 1231.1 14.8 1309.0






Rough Grass



Water

TOTAL**


TSS --- --- 100 52 67 80 0.7 90 40 ---NO3 + NO2 (as N) --- --- 1.2 1.5 1.7 2.3 0.5 1.1 0.7 ---

TP --- --- 0.7 0.8 1.0 1.3 0.1 0.3 0.1 ---COD --- --- 35 35 40 43 0.7 57 33 ---Lead --- --- 0.003 0.003 0.003 0.003 0.002 0.007 0.006 ---

Copper --- --- 0.010 0.010 0.010 0.010 0.024 0.047 0.014 ---Zinc --- --- 0.027 0.027 0.027 0.027 0.387 0.223 0.053 ---


TSS --- --- 8 3 22 0 0.8 211 19 263.2NO3 + NO2 --- --- 0.1 0.1 0.6 0.0 0.6 2.6 0.3 4.2

TP --- --- 0.1 0.0 0.3 0.0 0.1 0.7 0.1 1.2COD --- --- 3 2 13 0 0.8 133 16 167.1Lead --- --- 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Copper --- --- 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.2Zinc --- --- 0.0 0.0 0.0 0.0 0.5 0.5 0.0 1.0

Oil & Grease --- --- 0 0 0 0 1.0 28 0.3 29.3







Rough Grass



Water

TOTAL**


TSS 53 53 200 104 133 160 1 180 80 ---NO3 + NO2 (as N) 0.17 0.17 0.60 0.73 0.87 1.13 0.23 0.55 0.33 ---

TP 0.2 0.2 1.3 1.7 2.0 2.5 0.1 0.6 0.3 ---COD 53 53 71 71 80 87 1.3 113 67 ---Lead 0.002 0.002 0.007 0.007 0.007 0.007 0.004 0.015 0.012 ---

Copper 0.008 0.008 0.01 0.01 0.01 0.01 0.024 0.047 0.014 ---Zinc 0.010 0.010 0.013 0.013 0.013 0.013 0.193 0.111 0.027 ---


TSS 38.9 46.8 138.9 13.2 520.7 0.0 10.8 1888.3 227.6 2554.5NO3 + NO2 0.1 0.1 0.4 0.1 3.4 0.0 1.8 5.8 0.9 10.5

TP 0.1 0.2 0.9 0.2 7.8 0.0 0.9 6.0 0.7 13.7COD 38.9 46.8 49.1 9.0 312.4 0.0 10.8 1189.0 189.7 1644.9Lead 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.0 0.2

Copper 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.5 0.0 0.7Zinc 0.0 0.0 0.0 0.0 0.1 0.0 1.6 1.2 0.1 2.2

Oil & Grease 0.0 0.0 0.0 0.0 0.0 0.0 3.2 62.9 0.8 61.7




��

APPENDIX B STORMWATER INFRASTRUCTURE INVENTORY AND ANALYSIS The Rose Group began a field inventory of the stormwater infrastructure on the campus of UNC-Chapel Hill in September of 2001 to determine the location and condition of the stormwater structures and pipes on campus. The campus was divided into five major sub-basins. The major sub-basins are noted below:

• Meeting of the Waters Creek –ME-1 through ME-8 • Morgan Creek – MO-1 • Chapel Creek - CH-1 • Bolin Creek – BO-1 • Battle Creek – BA-1

The inventory originally concerned the location of all storm pipes greater than 12” in diameter and more than 24 feet in length (to eliminate driveway pipes). During field inventories it was observed that the campus storm water system contained an unusually large number of small diameter pipes ranging in size from 4-10” in diameter. Thus small diameter pipes were added to our data collection efforts. Approximately 3300 structures and pipes were located by the stormwater inventory. Pipe sizes range from as small as 4” in diameter to as large as 84” in diameter on the campus. Structures range in material type, construction technique, and accessibility. Data Dictionary Information The development database for the stormwater infrastructure consists of an ESRI ArcInfo coverage and a Microsoft Access database. The coverage contains the spatial data with very little attribute information. This is what is seen when a map is printed. The information in the coverage is linked to the Access database containing all the field collected attribute data through a unique identifier. The stormwater system at UNC consists of the following structure types:

TABLE 1. STRUCTURE TYPES

Structure Type Code Notes Catch Basin CB Inlet with a throat and a grate* Curb Inlet CI Inlet with a throat, but no grate Drop Inlet DI Inlet with a grate, but no throat

End Section ES Pipe end Junction

Box JB Typically a box with no surface opening (could be

underground) Manhole MH Any structure with a circular, non-grated lid

Other OT Slab Inlet SI Structure with a large, concrete lid

Pipe Junction PJ change in pipe size or material

*A throat is an elongated opening in a curb

��

There is only one coverage containing all the structures listed above. The Access database contains a separate table for each structure type. The table on the following page contains a complete listing of the attributes for point structures in the database, though individual attributes will not be in every point structure table.

��

TABLE 2. POINT STRUCTURE ATTRIBUTES

Attribute In Tables Notes ID All Unique identifier

Node Shape All Primary shape of structure (rectangular, circular, etc.) Length All Primary length dimension of structure parallel to road

Width All Primary width dimension of structure perpendicular to

road Depth All Depth of structure

Material All Primary material makeup of structure (brickwork,

cement, precast concrete, etc.)

Condition All Primary condition of structure (good, cracked,

sediment, etc.) %Obstructed All Percent obstruction of the outlet pipe of the structure

PictureID All Name of digital photograph Comment All

End Section Type ES Flared end, Headwall, Socket, Bell, etc.

In Sump? CB, CI, DI,

OT, SI Is there a sump in bottom of structure Grate Length CB, DI, OT Length of grate measured parallel to road Grate Width CB, DI, OT Width of grate measured perpendicular to road

Grate Obstruction CB, DI, OT Percent obstruction of the grate

Throat Length CB, CI, OT Length of throat Throat Height CB, CI, OT Height of throat Slab Height SI Height of opening between ground and slab top

Basin All Indicates which basin the structure is in Has Riser? DI, MH, OT Is there a riser in the structure?

Riser Material DI, MH, OT If there is a riser, what type of material X All X-coordinate at the vertical control point (paint dot) Y All Y-coordinate at the vertical control point (paint dot)

Elevation All Z-coordinate at the vertical control point (paint dot)

��

The following table lists the attributes in the pipe table.

TABLE 3.

PIPE ATTRIBUTES Attribute Notes

ID Unique identifier Upstream ID Identifier of the upstream point structure

Downstream ID Identifier of the downstream point structure Upstream Depth Pipe depth at the upstream point structure

Downstream Depth Pipe depth at the downstream point structure Upstream Elevation Pipe invert elevation at the upstream point structure

Downstream Elevation Pipe invert elevation at the downstream point structure Material Material makeup of pipe (cast iron, clay, pvc, rcp, etc.)

Condition Primary condition of structure (good, cracked, sediment, etc.) %Obstructed Percent obstruction of the pipe

Comment Pipe Shape Shape of pipe (arc, box, circular, elliptical)

Rise Pipe height (diameter if circular) Span Pipe width if pipe not circular, otherwise blank Type Type of pipe (Major, Minor, Channel, Unknown) Basin Indicates which basin the structure is in

Data Collection Process The process used to gather the stormwater information consisted of a multi-pass approach. The first pass consisted of the collection of attribute data and development of connectivity. Field personnel familiar with stormwater systems worked within each sub-basin collecting the information listed in the tables noted above. Attribute crews determined pipe connectivity and noted findings on maps and data collection forms. Each point or structure was also given a unique ID number and painted with a “dot” to represent the vertical control point. The vertical control point is the point to which all depth measurements were taken. Once the first pass was completed in a basin area, maps were distributed to a survey crew depicting the general location point and connectivity of structures. The survey crew visited each point structure and collected coordinates (x, y, and z) at the vertical control point. Each survey point was assigned a unique ID number created by the attribute crew. These two sets of data are then combined and incorporated into the ArcInfo coverage and the Access database. Once the GIS and database are populated, the system connectivity was defined and even revisited for quality control/quality assurance. (This effort generally reveals where field revisits are necessary). It should be noted that connectivity of the stormwater network for this project was limited to point structures containing pipes 12” in diameter and larger. Components and areas where connectivity could not be determined during the first pass were revisited to perform a more exhaustive reconnaissance. In many cases sediment accumulation and maintenance prevented actual validation of connection assumptions.

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Because our inventory included the smaller pipes (pipes less than 12” in diameter) these pipes were depicted in the GIS and the database. However, the source point structure for the minor system was not collected (upstream information not collected). In summary, all minor collection systems that drain into the “major” stormwater system were captured at the point they entered the “major” system. We observed that much of the minor system is randomly located with no particular attention to material type, elevation, or location. Not all systems were logically connected to roof drains as anticipated and a significant amount of minor drainage system connects to landscape and/or french drains. With concern for illicit connections, we have attempted to validate as much of the minor system drainage as possible by reviewing existing site plans where available. Structure Condition As might be expected, the majority of the structures within the sub-basin areas were catch basin and drop inlets. In most cases, junction boxes were visible only by looking into pipes within other nearby structures. Therefore, there may be some junction boxes in the sub-basin areas, which are not reflected in the inventory. The following table provides the number of structures by type within each of the sub-basin areas.

TABLE 4. NUMBER OF STRUCTURES BY TYPE

Basins Sub-

Basins Catch Basin

s

Curb Inlets

Drop Inlets

End Sections

Junction

Boxes

Manholes Total

MO MO-1 20 2 37 18 0 9 86 ME ME-1 54 4 108 6 10 31 213

ME-2 42 21 101 1 2 31 198 ME-3 34 1 107 6 3 21 172 ME-4 20 1 72 11 0 12 116 ME-5 90 8 116 28 2 15 259 ME-6 7 0 2 4 0 2 15

ME-7 24 0 6 11 0 1 42 ME-8 2 0 4 2 0 2 10

BO BO-1 8 2 29 0 0 6 45 BA BA-1 30 0 157 16 5 10 218 CH CH-1 5 0 0 1 0 0 6

Unknown 21 2 82 1 15 23 144 During the attribute collection in each sub basin area, the feature survey crews classified the condition of each structure. The surveyors classified the condition of the structures as:

• Good -Structure is undamaged and storm water can flow freely into and out of the structure.

• Cracked-Structure is cracked or broken. Crushed Structure has been crushed.

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• Bent-Structure has been bent, usually refers to corrugated metal endsections. • Sediment -Debris -Structure is severely obstructed with trash and debris such

that water cannot flow into (or out) of the structure. • Unknown -The structure is inaccessible. Unknown usually refers to pipes and

junction boxes but also could refer to inlets which have grates covered in asphalt.

TABLE 5.

CONDITION OF STRUCTURES BY TYPE Basin

s Sub-basin

Cracked

Debris

Fair Good

Missing Grate

Poor

Sediment

Submerged

Unknown

Total

MO MO-1 1 13 0 55 0 0 5 1 14 89 ME ME-1 5 1 0 172 1 0 14 0 20 213

ME-2 0 19 0 157 0 2 8 0 12 198 ME-3 4 8 0 128 0 0 24 1 7 172 ME-4 0 22 1 68 0 1 13 0 11 116 ME-5 0 3 0 215 0 0 3 0 38 259 ME-6 0 0 0 8 0 0 4 0 03 15 ME-7 0 5 0 31 0 0 4 0 02 42 ME-8 0 0 0 9 0 0 0 0 01 10

BO BO-1 2 4 0 29 0 0 10 0 0 45 BA BA-1 3 6 1 174 0 0 10 0 23 218 CH CH-1 0 0 0 3 0 0 3 0 0 6

Unknown

1 8 0 100 0 0 12 0 23 144

Pipe Condition Similar to above the attribute crew classified the condition of each pipe. The surveyors classified the condition of the structures as:

• Fair - Good -Structure is undamaged and storm water can flow freely into and out of the structure.

• Sediment -Structure is severely obstructed with trash and debris such that water cannot flow into (or out) of the structure.

• Unknown -The structure is inaccessible. Unknown usually refers to pipes and junction boxes but also could refer to inlets which have grates covered in asphalt.

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Major Pipe Summary Approximately 1260 major pipes were located. A summary of the major pipe condition is presented in the following table.

TABLE 6. CONDITION OF MAJOR CIRCULAR PIPE

Basins Sub-

basin Good Debris Sediment Unknown Total

MO MO-1 78 2 0 19 99 ME ME-1 267 0 2 55 324

ME-2 211 1 0 47 259 ME-3 287 2 7 103 399 ME-4 129 3 8 41 181 ME-5 241 0 0 46 287 ME-6 8 0 3 1 12 ME-7 42 1 2 8 53 ME-8 10 0 0 2 12

BO BO-1 80 0 4 28 112 BA BA-1 287 0 0 150 437 CH CH-1 2 1 1 0 3

Unknown 14 0 1 4 19

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Minor Pipe Summary Approximately 511 minor pipes were located. A summary of the minor pipe and condition is presented in the following table.

TABLE 7. CONDITION OF MINOR PIPE

Basins Sub-

basin Good Debris Sediment Cracked Total

MO MO-1 19 0 0 0 19 ME ME-1 54 0 0 1 55

ME-2 46 1 0 0 47 ME-3 102 1 0 1 104 ME-4 37 2 2 0 41 ME-5 45 0 0 0 45 ME-6 0 0 1 0 1 ME-7 8 0 0 0 8 ME-8 2 0 0 0 2

BO BO-1 27 0 1 0 28 BA BA-1 148 0 0 0 148 CH CH-1 0 0 0 0 0

Unknown 04 0 0 0 4

Complete and comprehensive tables detailing illicit discharges, pipe conflicts, and problem areas identified by our inventory and reported by grounds and housing representatives can be found in the report Infrastructure Inventory UNC Stormwater - April 2002 (Revised October 2002) along with a Digital database of Infrastructure Inventory. Approximately 120 specific stormwater problems have been defined to date that are either attributed to system capacity (flooding) or water quality (illicit discharge). Stormwater problems presented in these tables are categorized and ranked in severity from 0 to 3, with Category 0 representing limited concern for flooding or water quality to Category 3 representing severe problems and potential structural damage. A Category 3 ranking represents a system or problem that we believe requires immediate attention and/or further investigation. Pipe Conflicts The inventory revealed 13 scenarios where a larger pipe system was draining into a smaller pipe system along a major drainage system. Some of these systems likely contribute to the storm water concerns identified by the various departments. A summary of the pipe conflicts is presented in Table 9: Pipe Conflict Summary. Based on desktop analysis of the thirteen scenarios presented in Table 9, seven are not believed to cause flooding problems. However, there are six areas that appear likely to present potential flooding problems as a result of a pipe conflict. These pipes are near

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Phillips, Whitehead, Thurston Bowles, and Lineberger buildings, as well as Davis Library. The recommended solution is to analyze the entire system of concern and remove the undersized pipes and replace said pipes with pipe of appropriate diameter and material to convey the necessary stormwater flow for protection of flooding. This effort should also include a review of surface features and landscapes such that proper inlet placement can occur with respect to drainage and building protection without influencing overall site aesthetics. Further analysis of these areas is recommended to accomplish this task because in many instances the solution is not likely to create a series of interconnected pipes and infrastructure but rather a unique stormwater service that accommodates the local building topographic requirements, roof drain, associated basement drains, and landscapes. Trouble Spot Survey and Campus Interview(s) Department interviews were conducted with Grounds, Housing, Building, and Dean E. Smith Center Representatives. The purpose of these interviews was to identify known areas of flooding concerns and to relate these findings to our field inventory results. The Grounds Department provided detailed written records of repairs and maintenance from August 1994 to January 2002. Table 10 presents a summary of Grounds Department comments and records. Key individuals with Housing and Building Departments provided summaries of known flooding areas. These flooding concerns were limited to either building or equipment damage and did not include minor or nuisance flooding. Table 11 presents a summary of the interviews with Dean E. Smith Center, Building and Housing Departments. Representatives with the Dean E. Smith Center were also interviewed. Further interviews are recommended with the Medical and Hospital departments.

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WORKSHEET 5. VOLUME REDUCTIONS FOR PROJECT SPECIFIC MEASURES

PROJECT: Carrington Hall Addition

Green Roof Stormwater Storage

Layer Storage Storage(gal/sf) (cf/sf)

Hydrodrain FD60 0.20 0.027

SSm45 Moisture Mat 0.12 0.016

8" Soil at 20% capacity 1.00 0.134

Total: 1.32 0.18

Roof Area: 4475

TOTAL STORAGE: 4475 sf 0.18 (cf/sf) = 806 cfRoof Area (sf) x Storage (cf/sf) =

Infiltration Bed

Rain Garden

WORKSHEET 3 . VOLUME REDUCTION MEASURES

PROJECT: SUB-BASIN:

Required Storage Volume (from Worksheet 2): #DIV/0! cf

Proposed Measures

Measure Type AreaStorage Volume Provided per SF*

Net Storage Volume

(sf) (cf/sf) (cf)

Infiltration Bed 0Porous Pavement 0Infiltration Swale 0Tree Trench 0Green Roof 0Cistern � � �

� �

� � �

TOTAL STORAGE : ��

REQ'D STORAGE (WS 2): ��

EXCESS STORAGE: ��

* Provide supporting Design Calculations for each measure proposed

WORKSHEET 4 . PEAK HYDROGRAPH MITIGATION

Unit Peak Hydrograph Values For SCS TYPE II Rainfall Distribution

Tc = 0.1 hr Tc = 0.15 hrIa/P qu (csm/in) qu (csf/in) Ia/P qu (csm/in) qu (csf/in)

0.1 1010 3.6E-05 0.1 889 3.2E-050.2 973 3.5E-05 0.2 841 3.0E-050.3 936 3.4E-05 0.3 793 2.8E-05

0.35 885 3.2E-05 0.35 735 2.6E-050.4 806 2.9E-05 0.4 660 2.4E-05

Based on TR-55 Graphical Peak Discharge Tables and Formulas

Qp = qu x A x Q Note: User should input qu based on Ia/P and provided values. For other Tc values, refer to TR-55 Chapter 4, Exhibit 4-II and convert csm/in to csf/in by dividing csm/in by 52802

Volume Abstracted by Approved Methodsa (cf): ��

1-yr Storm, P = 3.0"Condition Area Ia

b Ia/P qu Runoff Qc Volume (cf) Qp

(ac) (in) (csf/in) (in) (Area x Q) (cfs)Before Dev �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! After Dev �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

W/Storage �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!








W/Storage �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!a From Worksheet 3b From Worksheet 2c Runoff Q (in) = (P - 0.2S)2/(P + 0.8S)

WORKSHEET 4 CONT. PEAK HYDROGRAPH MITIGATION

Unit Peak Hydrograph Values For SCS TYPE II Rainfall Distribution

Tc = 0.1 hr Tc = 0.15 hrIa/P qu (csm/in) qu (csf/in) Ia/P qu (csm/in) qu (csf/in)

0.1 1010 3.6E-05 0.1 889 3.2E-050.2 973 3.5E-05 0.2 841 3.0E-050.3 936 3.4E-05 0.3 793 2.8E-05

0.35 885 3.2E-05 0.35 735 2.6E-050.4 806 2.9E-05 0.4 660 2.4E-05

Based on TR-55 Graphical Peak Discharge Tables and Formulas

Qp = qu x A x Q Note: User should input qu based on Ia/P and provided values.

Volume Abstracted by Approved Methodsa (cf): ��



(ac) (in) (csf/in) (in) (Area x Q) (cfs)Before Dev � #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! After Dev �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!




(ac) (in) (csf/in) (in) (Area x Q) (cfs)Before Dev � #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! After Dev �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!


a From Worksheet 3b From Worksheet 2c Runoff Q (in) = (P - 0.2S)2/(P + 0.8S)

WORKSHEET 1 . CURVE NUMBERS AND 2-YR STORM RUNOFF

PROJECT: SUB-BASIN:

Existing Conditions: Land Use Types Within DrainageCover Type Area Area CN A * CN

(sf) (ac)

Woodland 0.00 55 0.00Cleared Woodland 0.00 65 0.00Planting Beds 0.00 70 0.00Meadow Lawns 0.00 74 0.00Lawn 0.00 79 0.00Grass Playfields 0.00 79 0.00 Buildings 0.00 98 0.00Roads/Parking 0.00 98 0.00Pathways & Rec 0.00 98 0.00

TOTAL: 0 0.000 0

WEIGHTED CN: #DIV/0! (A x CN) / A

Future Conditions: Land Use Types Within DrainageCover Type Area Area CN A * CN

(sf) (ac)

Woodland 0.00 55 0.00Cleared Woodland 0.00 65 0.00Planting Beds 0.00 70 0.00Meadow Lawns 0.00 74 0.00Lawn 0.00 79 0.00Grass Playfields 0.00 79 0.00Buildings 0.00 98 0.00Roads/Parking 0.00 98 0.00Pathways & Rec 0.00 98 0.00

TOTAL: 0 0.000 0

WEIGHTED CN: #DIV/0! (A x CN) / A

WORKSHEET 2 . CHANGE IN RUNOFF VOLUME FOR 2-YEAR STORM EVENT (3.6"/ 24 HR)

PROJECT: SUB-BASIN:

Condition Area CN S Ia Runoff Q*Runoff Volume

(ac) (in) (cf)

Before Dev �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! After Dev �� #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

�� #DIV/0!

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(REQ'D STORAGE VOLUME)

S = 1000/CN - 10Ia = 0.2S*Runoff Q (in) = (P - 0.2S)2/(P + 0.8S)

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I

R E F E R E N C E S

REFERENCES

Allen, Eldon P. and Wilson, William F., Geology and Mineral Resources of Orange County, North Carolina. North Carolina Department of Conservation and Development, Raleigh, NC. Bulletin 81, 1968.

Arendt, Randall. Growing Greener, Putting Conservation into Local Plans and Ordinances. Natural Lands Trust, American Planning Association, American Society of Landscape Architects. Island Press, Washington, DC. 1999.

Baird, Charles F., Dybala, Timothy J., Jennings, Marshall, Ockerman, Darwin J., Characterization of Nonpoint Sources and Loadings to Corpus Christi Bay National Estuary Program Study Area. 1996.

Cape Fear River Basinwide Water Quality Plan. North Carolina Department of Environment and Natural Resources, Division of Water Quality. February, 2000.

Center for Watershed Protection. Design of Stormwater Filtering Systems. Prepared for the Cheasapeake Research Consortium. 1996.

Center for Watershed Protection, Stormwater Pollution Source Areas. Technical Note #105 from Watershed Protection Techniques. 3(1): 609-612. 1997.

Center for Watershed Protection, New Developments in Street Sweeper Technology. Technical Note #103 from Watershed Protection Techniques. 3(1): 601-604. 1997.

Craul, Philip J., Urban Soils Applications and Practices. John Wiley & Sons, Inc. New York, New York. 1999.

Epperson, D.L., Johnson, G.L., Davis, J.M. and Robinson, P.J., Weather and Climate in North Carolina. Agricultural Extension Service, North Carolina State University, Raleigh, North Carolina. 1987.

Ferguson, Bruce K., Stormwater Infiltration, Lewis Publishers, Boca Raton, Florida. 1994.

Federal Highway Administration, Ultra Urban Best Management Practices (Draft, Fact Sheet - Street Sweepers. Office of Environment and Planning, FHWA, Washington, DC, pp.127-130. 1997.

Driscoll, E.D., Shelley, P.E., and Strecker, E.W., Pollutant loadings and impacts from highway stormwater runoff, Volume III: Analytical investigation and research report: Federal Highway Administration Final Report FHWA-RD-88-008. 1990.

Godfrey, Michael A. Field Guide to the Piedmont. The Natural Habitats of America’s Most Lived-in Region, from New York City to Montgomery, Alabama. University of North Carolina Press. 1997.

II

R E F E R E N C E S

III

R E F E R E N C E S

Federal Register Phase II Stormwater NPDES Regulations. Vol 64 #235 p.68722-68852 Dec. 1999.

Hoffman, Charles W. and Gallager, Patricia E., Geology of the Southeast Durham and Southwest Durham 7.5 Minute Quadrangles, North Carolina. Bulletin 92, North Carolina Geological Survey, Division of Land Resources, Raleigh, NC. 1989.

Horton, Wright J., and Zullo, Victor A., The Geology of the Carolinas. Carolina Geological Society Fiftieth Anniversary Volume. The University of Tennessee Press, Knoxville, TN. 1991.

Ku, Henry F.H., and Simmons, Dale L., Effect of Urban Stormwater Runoff on Groundwater Beneath Recharge Basins on Long Island, New York, Water-Resources Investigations Report 85-4088, Syosset, New York Geological Survey. 1986.

New Jersey Stormwater Best Management Practices Manual. New Jersey Department of Environmental Protection, Division of Watershed Management, Trenton, NJ. April 2004.

Rogers, John J.W., History and Environment of North Carolina’s Piedmont. Department of Geology, University of North Carolina at Chapel Hill, July 1999.

Schueler, T. Environmental Land Planning Document Series: Site Planning for Urban Stream Protection. Center for Watershed Protection, Metropolitan Washington Council of Governments, and the US Environmental Protection Agency. Washington DC. 1995.

Soil Survey of Durham County, North Carolina. United States Department of Agriculture. Soil Conservation Service in cooperation with North Carolina Agricultural Experiment Station. 1960.

Soil Survey of Orange County, North Carolina, United States Department of Agriculture, Soil Conservation Service in cooperation with North Carolina Agricultural Experiment Station and Orange County Board of Commissioners. June 1977.

State Climate Office of North Carolina. Aspects of NC Climate. www.nc-climate.ncsu.edu.

Stormwater Utility, Development and Implementation Study Committee. Recommendations for a Comprehensive Stormwater and Floodplain Management Program for the Town of Chapel Hill and southern Orange County. Final Report to Chapel Hill Town Council, Chapel Hill, NC. November 26, 2001.

Suthersand, R.C., and S.L. Jelen. “Contrary to Conventional Wisdom, Street Sweeping Can be an Effective BMP.” Advances in Modeling the Management of Stormwater Impacts, Vol.5 Ed., W. James. Computational Hydraulics International. Guelph, Ontario. Pp. 170-190. 1997.

Thompson, William J. and Sorvig, Kim. Sustainable Landscape Construction: A guide to green building outdoors. Island Press, Washington, DC. 2000.

Town of Chapel Hill Data Book. Planning for Chapel Hill’s Future: Annual Compilation of Town and Regional Data. Chapel Hill Planning Department, Chapel Hill, NC. February 2000.

Town of Chapel Hill. Development Ordinance. Stormwater Management Performance Standards for development and redevelopment in the Office/Institutional-4 (O1-4) Zoning District, Chapel Hill, NC. July 2001.

U.S. Environmental Protection Agency, Results of the Nationwide Urban Runoff Program, Volume 1: Final Report. Water Planning Division, Washington, DC., December 1983.

Walker, Laurence C. and Oswald, Brian P., The Southern Forest. Geography, Ecology and Silviculture. CRC Press LLC, Boca Raton, Florida. 2000.

STUDIES BY THE ROSE GROUP AS PART OF THE STORMWATER MANAGEMENT PLAN

The Rose Group. Infrastructure Inventory UNC Stormwater Infrastructure Inventory - Prepared for UNC-CH. April 2002. (Revised October 2002).

The Rose Group. Preliminary Backbone Study Rams Head Plaza - November 7, 2002. Prepared for UNC-CH.

The Rose Group. Preliminary Study Hospital Parking -January 14, 2003. Prepared for UNC-CH.

The Rose Group. UNC Comprehensive Backbone Study –January 30, 2003. Prepared for UNC-CH.

The Rose Group. UNC Volume Reduction Study April 4, 2003 (Revised April 10, 2003). Prepared for UNC-CH.

The Rose Group. UNC Volume Reduction Study-Kenan, Boshamer, North Campus, Hospital - April 16, 2003.

STUDIES BY T.H. CAHILL ASSOCIATES AS PART OF THE STORMWATER MANAGEMENT PLAN

Hydrologic & Hydraulic Model Analysis of Potential Flooding Conditions with Stormwater Mitigation Recommendations, University of North Carolina - Chapel Hill, Meeting of the Waters Watershed, Sub-basin ME-1 (March 19, 2004)

Hydrologic & Hydraulic Model Analysis of Potential Flooding Conditions with Stormwater Mitigation Recommendations: UPDATE, University of North Carolina - Chapel Hill, Meeting of the Waters Watershed, Sub-basin ME-1 (November 5, 2004)

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