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Chapter 3. Controlling Urban Runoff 153 

## 6

. BMP Fact Sheets 1

1 

### 6.1 Introduction 2 The following BMP fact sheets are included in this section. Each fact sheet includes a description 3 of the practice, targeted pollutants, photos/diagra ms, constraints/limitations, effectiveness, 4 design, maintenance, and costs. 5 6.1 Rainwater harvesting 6 6.2 Green roofs 7 6.3 Blue roofs 8 6.4 Bioretention 9 6.5 Soil restoration 10 6.6 Reforestation/urban forestry 11 6.7 Street sweeping 12 6.8 Constructed wetlands 13


### 6.1.1 Additional BMP fact sheets 14 In addition to the fact sheets included in this sec tion, EPA has published information on fact 15 sheets on other BMPs at the Green Infrastructure technology w ebsite: 16 http://cfpub.epa.gov/npdes/greeninfrastructure/tech nology.cfm 17 Fact sheets on these technologies are also availabl e at EPA’s Menu of BMPs website: 18 http://cfpub.epa.gov/npdes/stormwater/menuofbmps/in dex.cfm?action=min_measure&min_meas 19 ure_id=5 20 These BMPs include : 21

• Downspout disconnection • Brownfield redevelopment

• Planter boxes • Infill and redevelopment

• Rain gardens • Green parking

• Permeable pavements • Pocket wetlands

• Vegetated swales • Compost Blanket Downspout disconnection 22 Planter boxes 23 Rain gardens 24 Permeable pavements 25 Vegetated swales 263/15/20 2

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Chapter 3. Controlling Urban Runoff 154 Brownfield redevelopment 1 Infill and redevelopment 2 Green parking 3 Green streets and highways 4 Pocket wetlands 5


### 6.1.2 Performance estimate summaries for Infiltrati on Practices 6 The performance of low-impact development practices varies significantly based on the design 7 and the regional climate. The performance of these practices was recently reviewed for the 8 Chesapeake Bay region to estimate the capability fo r volume control and pollutant reduction. 9 The Mid-Atlantic Water Program (MAWP) housed at the University of Maryland (UMD) led a 10 project during 2006-2009 to review and refine defin ition and effectiveness estimates for BMPs 11 implemented and reported by the Chesapeake Bay wate rshed jurisdictions prior to 2003 12 (Developing Best Management Practice Definitions an d Effectiveness Estimates for Nitrogen, 13 Phosphorus, and Sediment in the Chesapeake Bay, Dec ember 2009 ( “ BMP Effectiveness 14 Report ” ) www.chesapeakebay.net/websitesearchresults.aspx?men uitem=19557 ). The urban 15 stormwater BMPs reviewed by the MAWP are posted at 16 http://archive.chesapeakebay.net/pubs/BMP_ASSESSMEN T_REPORT.pdf . The low impact 17 development BMPs reviewed and their definition as r eported in BMP assessment are as follows: 18
Bioretention: An excavated pit backfilled with engineered media, topsoil, mulch, and vegetation. 19 These are planting areas installed in shallow basin s in which the storm water is temporarily 20 ponded and then treated by filtering through the be d components, and through biological and 21 biochemical reactions within the soil matrix and ar ound the root zones of the plants. 22 Permeable Pavement and Pavers: Pavement or pavers that reduce runoff volume and tr eat water 23 quality through both infiltration and filtration me chanisms. Water filters through open voids in 24 the pavement surface to a washed gravel subsurface storage reservoir, where it is then slowly 25 infiltrated into the underlying soils or exists via an underdrain. 26 Infiltration Trenches and Basins: A depression to form an infiltration basin where se diment is 27 trapped and water infiltrates the soil. No underdra ins are associated with infiltration basins and 28 trenches, because by definition these systems provi de complete infiltration. 29 Filters: Filters capture and treat runoff by filtering thro ugh a sand or organic media. 30 Vegetated Open Channels: Open channels are practices that convey stormwater runoff and 31 provide treatment as the water is conveyed, include s bioswales. Runoff passes through either 32 vegetation in the channel, subsoil matrix, and/or i s infiltrated into the underlying soils. 33 The effectiveness summary from the BMP Assessment R eport in is provided in Table 3-44. The 34 BMP Assessment Report provides a summary of assumpt ions, data sources, maintenance 35 consideration, and other factors related to these L ID practices in the Chesapeake Bay area. 36 Among the assumptions used in preparation of the ef fectiveness estimates was that the BMPs 37 were designed for an approximate 1 inch to 1.5 inch storm event across the impervious drainage 38 area. This 1 inch to 1.5 inch rainfall is approxima tely the 95 th percentile rain event in the 393/15/20 2

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Chapter 3. Controlling Urban Runoff 155 Chesapeake Bay area. In reviewing the effectiveness values in this table, it is important to note 1 the variability in the estimates, and that the majo rity of the pollutant removal is associated with 2 the volume reduction that occur from either infiltr ation or evapotranspiration. 3 Table 3-44. Effectiveness summary from the BMP Asse ssment Report 4

EMC Based Removal (PR) Runoff Reduction (RR) Mass Based Removal

(TR) expressed as removal from collection areas (acres) TP TN* TSS TP TN TSS Bioretention C/D soils, underdrain 37 10 50 15 45 25 55 A/B soils, underdrain 37 10 50 65 75 70 80 A/B soils, no underdrain 37 10 50 80 85 80 90 ± 15 ± 20 ± 15 Filter All (sand, organic, peat) 60 40 80 0 60 40 80 ± 15 ± 10 ± 10 Vegetated Open Channels C/D soils, no underdrain 10 10 50 0 10 10 50 A/B soil, no underdrain 10 10 50 40 45 45 70 ± 20 ± 20 ± 30 Bioswale 37 10 50 65 75 70 80 ± 15 ± 20 ± 15 Permeable Pavement (no sand/veg)

C/D soils, underdrain 10 0 50 10 20 10 55 A/B soils, underdrain 10 0 50 45 50 45 70 A/B soils, no underdrain 10 0 50 75 80 75 85 ± 15 ± 20 ± 15 Permeable Pavement (with sand, veg) C/D soils, underdrain 10 10 50 10 20 20 55 A/B soils, underdrain 10 10 50 45 50 50 70 A/B soils, no underdrain 10 10 50 75 80 80 85 ± 15 ± 15 ± 10 Infiltration Practices (no sand/veg) A/B soils, no underdrain 25 0 95 80 85 80 95 ± 15 ± 15 ± 103/15/20 2

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Chapter 3. Controlling Urban Runoff 156 EMC Based Removal (PR) Runoff Reduction (RR) Mass Based Removal

(TR) expressed as removal from collection areas (acres) TP TN* TSS TP TN TSS Infiltration Practices (with sand/veg) A/B soils, no underdrain 25 15 95 80 85 85 95 ± 15 ± 10 ± 10 Source: Simpson, Thomas, and Sarah Weammert, Developing Best Management Practice Definitions and Effectiveness Estimates for Nitrogen, Phosphorus, a nd Sediment in the Chesapeake Bay, Final Report, December 2009. 

### 6.2 Rainwater Harvesting 1 

### Description of Practice 2 Rainwater harvesting can play an important role in managing stormwater runoff and can reduce 3 both the costs and energy needed to convey and trea t runoff offsite. Rain barrels and cisterns can 4 be used to reduce runoff volume and mitigate peak r unoff flow rates for small and medium storm 5 events. At the present, rainwater collected in harv esting systems is typically only used for non6 potable applications, such as irrigation, toilet fl ushing, and vehicle washing but uses may expand 7 as demand for water increases. In addition to reduc ing stormwater runoff, rainwater harvesting 8 has the secondary benefit of reducing potable water demand because non-potable uses represent 9 up to 40 percent of overall household water demand. Rooftop runoff, because it typically 10 contains low pollutant loads and is easily collecte d , is the source of most water collected in 11 rainwater harvesting systems. 12 Harvested rainwater can be routed and stored in two main types of vessels called cisterns or 13 rainbarrels. Cisterns generally have a much larger capacity than rainbarrels. Cisterns can be 14 designed to hold hundreds or thousands of gallons. Rainbarrels most often hold between 55–250 15 gallons with 55–75 gallon barrels being the most co mmonly used sizes. To capture the rainwater, 16 roof downspouts are piped to the rainbarrel or cist ern. Most residential rainbarrels are installed 17 outside as are many cisterns. However, cisterns can be installed inside residential and non18 residential buildings, outside and above or below g rade. Bypass drains or systems are used to 19 divert excess volume when the rainbarrel or cistern is full. 20 Some systems require the use of filtration or disin fection systems depending on the intended use 21 and the size of the system. Rainbarrels typically d o not require such systems. Filtration and 22 disinfection systems are used to reduce fouling, cl ogging, bacterial growth, slime formation and 23 to treat the rainwater for its intended uses. 24 In most areas of the country, the use of rainbarrel s and cisterns is encouraged mainly to reduce 25 the volume of runoff discharged from impervious sur faces. In arid or semi-arid areas or areas of 26 period drought rainwater harvesting systems can pla y an important role in the provision of 27 supplemental irrigation or wash waters. Around the globe, rainwater collection systems are often 28 used to provide potable water. In the United States the use of harvested rainwater for potable 29 uses is restricted due to public health concerns. 303/15/20 2

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Chapter 3. Controlling Urban Runoff 157 Rainwater harvesting systems are most effectively u sed to reduce runoff volume when they are 1 integrated into a treatment train or system of prac tices that may include green roofs, permeable 2 pavements or raingardens/bioretention cells. 3 To optimize system performance, the system should b e managed either manually or 4 automatically to discharge the captured volume befo re the next significant storm event occurs. 5 Such management strategies help to ensure that the maximum cistern/rain barrel capacity is 6 available when a rain event occurs. For example, so aker hoses can be used with rainbarrels to 7 slowly drain the rainbarrel in periods of non-irrig ation use and automatic real-time control 8 systems can be used for large non-residential syste ms to control the timing of and the release rate 9 of water from the cistern to ensure capacity is ava ilable to capture the next storm. 10 

### Hydrologic Performance and Targeted Pollutants 11 Hydrologic Performance 12
**Volume Reduction Peak Flow Reduction**  **Groundwater Recharge**
  
Key:  High effectiveness  Medium effectiveness  Low effectiveness 13 Targeted Pollutants 14 **Sediment Nitrogen Phosphorus Metals Oil & Grease Ba cteria Temperature** 

       Key:  High effectiveness  Medium effectiveness  Low effectiveness 153/15/20 2

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Chapter 3. Controlling Urban Runoff 158 

### Photos and Diagrams 1

2 Figure 3-22. Typical Rainwater Harvesting System 3 Source: NC Division of Water Quality. Technical Guidance: Stormwater Treatment Credit for Rainwater Harvesting Systems 

### Common Feasibility Constraints and Limitations 4

• Requires a dedicated plumbing system for indoor use 5

• Optimal performance requires active management to e nsure that storage containers are 6 emptied between storms. 7

• Local ordinances may restrict downspout disconnecti on or indoor use of harvested water. 8



### Runoff Volume and Pollutant Load Removal Estimates 9 The volume retained in a storm event is determined by the size of the storage container and its 10 available volume at the time of the storm. Careful operation of the system to ensure that cisterns 11 and rain barrels drain completely prior to a rain e vent can help to maximize the available 12 volume. The use of real-time control systems can in crease performance significantly. 13 Pollutant removal by rainwater harvesting is minima l, and is generally limited to settling of 14 suspended solids. Water quality may degrade in a ci stern if bacteria are allowed to grow. 153/15/20 2

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Chapter 3. Controlling Urban Runoff 159 

### Practice Design 1 Sizing is based on rainfall patterns, drainage area , water demand, and space and/or budgetary 2 constraints. Cisterns should be sized to store wate r from multiple events, or to empty between 3 events, if capacity for back-to-back storms is need ed. 4 Proper cistern capacity is calculated by balancing the expected rainfall volume with the 5 anticipated water demand. Additional capacity may b e incorporated to allow extended storage of 6 rainwater for use during dry periods. 7 Design considerations include : 8

• Piping for harvested rainwater should be labeled to prevent accidental use for potable 9 applications. 10

• Rain barrels and cisterns should be fitted with eme rgency overflows. 11

• Cisterns constructed belowground must be fitted wit h pumps to deliver collected water. 12

• Systems for indoor uses such as toilet flushing sho uld be dual piped with potable water 13 for back-up. A backflow prevention assembly should be used to prevent cross14 contamination of the potable supply line. Local bui lding codes should be consulted. 15

• Pretreatment may be desired prior to storage to pre vent fouling of the storage tank. 16 Screening, settling of suspended solids, and oil an d grease separation (for parking lot 17 runoff) may be beneficial. The first flush of runof f may be diverted from the storage tank 18 to remove debris. 19

• Treatment requirements for stored rainwater vary by municipality and intended end use. 20 Typically, no treatment is required for outdoor irr igation, while filtration and/or UV 21 disinfection may be required for indoor nonpotable uses. 22

• Outdoor cisterns should be screened at each opening to prevent insects from entering. 23 American Rainwater Catchment Systems Association/Am erican Society of Plumbing Engineers 24 issued Rainwater Catchment Design and Installation Standar ds (August 2009) to assist in 25 properly and safely implementing systems. Several l ocalities have implemented or adopted 26 standards as part of their building codes. 27


### Maintenance Considerations and Resources 28 A typical maintenance schedule is provided here. Ma intenance needs will vary based on the type 29 of system and location. 303/15/20 2

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Chapter 3. Controlling Urban Runoff 160 1 Figure 3-23. Typical maintenance schedule for a rai nwater harvesting system. 2 Source: Federico, et. al., Geosyntec Consultants, Technical Memorandum: Large-Scale Cistern Standards , Report to Los Angeles County Department of Public Works, Dece mber 2009. 

### Costs and factors affecting cost 3 55-gallon rain barrels typically cost $50–100 for p refabricated units, or $30 for do-it-yourself 4 kits. 5 For cistern tanks, costs depend on the material use d for construction, and costs are similar to 6 other water storage tank systems. A tool for estima ting tank and pump costs is available from the 7 Water Environment Federation (WERF), the User’s Guide to the BMP and LID Whole Life Cost 8 Model, Version 2.0 , and associated spreadsheet tool. 9

Table 3-45. Cistern tank costs. 10 Cistern Tank Cost by Type ($/gallon, installation n ot included), 2009

Fiberglass Steel Plastic Concrete 10,000 gal and up 500-15,000 gal 50-1,500 gal 2,000 gal and up $ 1.33 $ 2.51 $ 1.43 $ 1.66 Source: WERF BMP and LID Whole Life Cost Model, Version 2.0 Costs for large cistern systems are dependent on ma ny site-specific factors, such as whether 11 excavation is required for underground units. Cost items applicable to systems used for irrigation 12 can include : 13

• Piping and pretreatment (screening) 14

• Tank, pumps, valves 153/15/20 2

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Chapter 3. Controlling Urban Runoff 161 • Site preparation 1

• Concrete pad for above-ground; excavation for burie d 2 Example system costs are provided in Table 3-46. 3 Table 3-46. Summary of Cistern System Costs with Pr oject Characteristics 4

Site Capacity (gallons) Construction

Material New/Retrofit

Yr Installed Location Estimated Cost Landscape Architecture 1 Library, Tucson, AZ 11,600 Steel and Fiberglass New 2007 Aboveground $17,000

(total cost) Fairmount Square 1 Grand Rapids, MI 30,000 Concrete New Buried $40,000 (total cost) Redbud Center 1 Austin, TX 31,000 Steel New 2008 Aboveground $250,000

(total cost) Santa Monica Main 1 Library, CA 200,000 Concrete New 2006 Buried $700,000 (total cost) Mark Miller Toyota 2 Salt Lake City, UT 1 @ 8000 1 @ 2000 Concrete New 2008 Buried $22,000 (total cost) Hypothetical Office 2 Building, Arlington, VA 10,000 Fiberglass New 2008 Buried $179,000 (estimated total) Open Charter Elementary, Westchester CA 2 110,000 Modified RainStore3 Infiltration System New 2004 Buried $500,000 (not incl. design) Hall House, Los Angeles, CA 1 3,600 Polypropylene Retrofit 1998 Partially Buried $25,000

(installed) Center for Community Forestry, Los Angeles, CA 1 216,000 Concrete New 2008 Buried $400,000 (excludes soft costs, distribution system)
1 Federico, et. al., Geosyntec Consultants, Technical Memorandum: Large-Scale Cistern Standards , Report to Los Angeles County Department of Public Works, December 2009.fairmoun 2 Water Environment Research Federation, User’s Guide to the BMP and LID Whole Life Cost Model, Ve rsion 2.0 , 2009.


### References 5 American Rainwater Catchment Systems Association, www.arcsa.org 6 Cabell Brand Center. 2009. Virginia Rainwater Harvesting Manual, Version 2.0 . Salem, VA. 7 (Draft Form) www.cabellbrandcenter.org ; 8 http://cabellbrandcenter.org/RWH_Manual2009.pdf 9 Credit Valley Conservation. 2008 . Credit River Stormwater Management Manual . Mississauga, 10 Ontario; www.creditvalleyca.ca/sustainability/lid/stormwater guidance/index.html 11 Federico, et. al.,Geosyntec Consultants . 2009. , Technical Memorandum: Large-Scale Cistern 12 Standards , Report to Los Angeles County Department of Public Works

. 13 , December 2009 143/15/20 2

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Chapter 3. Controlling Urban Runoff 162 Georgia Department of Community Affairs. 2009. Georgia Rainwater Harvesting Guidelines, 1 Draft , April 2009

. 2 Gowland, D. and T. Younos. 2008. Feasibility of Rainwater Harvesting BMP for Stormwa ter 3 Management . Virginia Water Resources Research Center. Special Report SR38-2008. 4 Blacksburg, VA 5 North Carolina Division of Water Quality. 2008. Technical Guidance: Stormwater Treatment 6 Credit for Rainwater Harvesting Systems . Revised September 22, 2008. Raleigh, NC. 7 http://h2o.enr.state.nc.us/su/documents/RainwaterHa rvesting_Approved.pdf 8 North Carolina State University, Biological and Agr icultural Engineering . Urban Waterways: 9 Permeable Pavements, Green Roofs, and Cisterns

. 10 www.bae.ncsu.edu/stormwater/PublicationFiles/BMPs4L ID.pdf 11 Seattle, Washington Oregon , Department of Planning and Development . 2009. , Rainwater 12 Harvesting for Beneficial Use, Client Assistance Memo 520. April 2009. 13 Texas A&M University, AgriLife Extention Service, 14 http://rainwaterharvesting.tamu.edu/index.html 15 Texas Water Development Board . 2005. , The Texas Manual on Rainwater Harvesting – Third 16 Edition , 2005

. 17 US Environmental Protection Agency, Office of Water

. 2008. Municipal Handbook : Rainwater 18 Harvesting Policies , December 2008

. 19 www.epa.gov/npdes/pubs/gi_munichandbook_harvesting. pdf 20 Virginia Department of Conservation and Recreation, Design Specification No.6 and Design 21 Spreadsheet www.chesapeakestormwater.net/storage/first-draft-ba ywide-design22 specificationsi/BAYWIDE%20No%206%20RAIN%20TANKS%20A ND%20CISTERNS. 23 pdf 24 Water Environment Research Federation . 2009. , User’s Guide to the BMP and LID Whole Life 25 Cost Model, Version 2.0 , 2009

. 263/15/20 2

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Chapter 3. Controlling Urban Runoff 163 

### 6.3 Green roofs 1 

### Description of Practice 2 Green roofs attenuate flow and provide storage and evapotranspiration of stormwater. They are 3 typically designed with an impermeable membrane tha t is root resistant, an engineered soil 4 medium, plants, and in many cases an underdrain sys tem. Some green roofs also have leak 5 detection systems. The design of green roof systems significantly impacts performance. The two 6 main categories of green roof designs are : 7

• Extensive, which have a shallow planting media laye r (typically 2–6 inches ” ) and low8 growing, drought tolerant plants. 9

• Intensive, which have a deeper media layer, and can be planted with a wider variety of 10 plants, including trees and shrubs. Intensive green roofs can be fitted with walkways and 11 used as recreational areas. 12 Rain falling onto green roofs is both detained and retained in the soil medium. When the soil 13 medium becomes saturated, the excess water percolat es through to the drainage layer and is 14 discharged through the roof downspouts. In between storm events, water absorbed by the soil 15 media is returned to the atmosphere by evapotranspi ration. Depending on the design and climate 16 pattern of the region, green roofs can provide sign ificant stormwater volume reduction on an 17 annual basis, decrease peak flow rates and help to restore hydrologic function of the watershed 18 by absorbing and attenuating runoff. 19 In addition to providing stormwater retention, gree n roofs can be designed to provide ancillary 20 benefits, such as enhancing site aesthetics, urban habitat for birds and insects, insulation value 21 for energy conservation and increasing the longevit y of roofing materials. 22 Green roofs are common in Europe, but have only rec ently gained popularity in US as a practice 23 for mitigating stormwater runoff. The International Green Roofs Projects Database 24 ( www.greenroofs.com ) lists over 1,000 green roof projects, mainly in t he United States. 25 

### Hydrologic Performance and Targeted Pollutants 26 Hydrologic Performance 27
**Volume Reduction Peak Flow Reduction Groundwater Re charge** 
  
Key:  High effectiveness  Medium effectiveness  Low effectiveness 28 Targeted Pollutants 29 **Sediment Nitrogen Phosphorus Metals Oil & Grease Ba cteria Temperature** 

       3/15/20 2

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Chapter 3. Controlling Urban Runoff 164 Key:  High effectiveness  Medium effectiveness  Low effectiveness 

### Photos and Diagrams 1
2

3 Figure 3-24. ASLA Headquarters Green roof 4 Source: The Low Impact Development Center 5

6 Figure 3-25. Green Roof Section 7 Source: MDE Stormwater Design Manual 83/15/20 2

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Chapter 3. Controlling Urban Runoff 165 

### Common Feasibility Constraints and Limitations 1

• Slopes should be less than 30 percent % . Installations on pitched roofs require 2 stabilization structures to prevent migration of th e soil medium. Specialized drains are 3 typically required for slopes above 5 percent %

. 4

• Roofs must be able to bear the load of a fully satu rated medium. Extensive green roof wet 5 weight is approximately 6 to 7 pounds per square fo ot per inch of depth. 6

• Construction costs include transporting materials t o a roof, which may require a crane. 7

• Costs of green roof construction typically make it a cost-effective option only in dense 8 urban areas. 9



### Runoff Volume and Pollutant Load Removal Estimates 10 Runoff volume removal is a function of the green ro of area, the specifics of the green roof 11 design, and the local climate and rainfall pattern. Green roofs can retain the full volume of small 12 storms, and they are commonly designed to detain br ief periods of high intensity rainfall. 13 Reported results for extensive roofs are summarized here. 14

Table 3-47. Performance Estimates for Annual Flow R etained, Summer Flow Retained, and Peak 15 Flow Shaving for Green Roofs 16

Performance

Measure Performance

Estimate Location Depth of Media (not including submedia

layers) Source 50% Philadelphia 3.5 to 4 inches EPA, 2009 75% Washington, D.C. 3 - 18 inches Glass, 2007 65-70% East Lansing, MI 1 -2.4 inches VanWoert, 200 5 56% Portland, OR 5 inch Portland BES, 2008 Annual Flow Retained

26% - 86% National Range Various Portland BES, 2008 Summer Runoff 95% Philadelphia 3.5 to 4 inches EPA, 2009

30% to 96% National Range Portland BES, 2008 Peak Flow Shaving 60% Portland, OR 5 inch Portland BES, 2008
Pollutant removal in green roofs is strongly depend ent on the specifics of the design, and on rates 17 of atmospheric deposition. Studies have shown that green roofs do not often provide pollutant 18 reductions, however, it is noted that the concentra tion of pollutants in direct rainfall is very low 19 (therefore, there is relatively little pollutant to remove). Temporary export of nutrient may occur 20 during initial establishment of the media and plant s. Poorly designed green roof soil media can 21 lead to export of low concentrations of nutrients a nd solids from the media, fertilizer and plants. 22 For this reason, it is preferable to discharge the runoff from green roofs into bioretention or other 23 unit if pollutant reduction is needed in addition t o the volume reduction (EPA 2009). Green 24 roofs, however, have been shown to export lower lev els of pollutants than conventional roofs. 253/15/20 2

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Chapter 3. Controlling Urban Runoff 166 Material selection is an important consideration. M any roofing materials can export toxic 1 chemicals that may be used in their construction (C lark et al, 2008). 2 

### Practice Design 3 Green roofs are most often constructed on flat or s hallowly sloped roofs, but roofs with slopes up 4 to 30 percent % accommodate green roofs with the use of mesh, stab ilization panels, or battens. 5 The area covered by green roofs is typically limite d to 50 – 80 percent of the total roof area due 6 to the need to accommodate HVAC (heating, ventilati on and air conditioning) or other 7 equipment (e.g. cell towers or solar panels) and ro of access or other penetrations. Green roofs 8 have also been designed to accommodate solar panels

. 9 A typical green roof profile would include the foll owing layers: 10

• Vegetation layer 11

• Engineered growth media 12

• Separation geotextile 13

• Semi-rigid plastic geocomposite drain or mat 14

• Root barrier 15

• Waterproofing membrane 16
Plant Selection - Plant selection varies depending on the type of g reen roof installed. Extensive 17 green roofs should be planted with low-growing, dro ught tolerant plants, such as succulents. 18 Sedums are frequently used. Intensive green roofs, which have deeper soil media, can 19 accommodate a much wider variety of plants, includi ng trees and shrubs. Intensive green roofs 20 often require irrigation to support the larger plan ts. 21 Soil medium - To minimize the potential for nutrient export, t he soil medium should have a high 22 mineral content. Use of compost has been found to p roduce elevated levels of nitrogen and 23 phosphorus in effluent, at least in the short term (Moran et al, 2004). 24


### Maintenance Considerations and Resources 25 Maintenance requirements vary depending on design s pecifics, with extensive green roofs 26 typically requiring less maintenance than intensive green roofs. Maintenance typically includes : 27

• Periodic irrigation during plant establishment and dry periods. 28

• Periodic weeding, fertilization (if needed), and in fill planting 29

• Periodic inspection of drainage outlets and waterpr oof membrane. 30 

### Costs and factors affecting cost 31 Costs depend on the media depth, the number and typ e of additional structural components in the 32 design, the vegetation selected, and the need for s tructural roof modifications. Costs for 33 extensive green roofs typically range from $8–$14 p er square foot (PADEP, 2006). The 343/15/20 2

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Chapter 3. Controlling Urban Runoff 167 installation cost of the green roof is partially of fset by increasing the life of the underlying roof, 1 and reducing heating and cooling demand within the building. 2 Costs were reported to vary primarily by the instal lation type (WERF , 2009, and Portland BES , 3 2008): 4

• Modular, tray-type installations: $19.50 per square foot 5

• Custom applications with media spread across the su rface: $8.75 per square foot

. 6 Green roofs reduce energy costs and extend roof lif e. Green Roofs for Healthy Cities 7 ( www.greenroofs.org ) provides a calculator to estimate the long term s avings. 8 A cost-benefit analysis of a hypothetical green roo f concluded that green roofs had a higher net 9 present value for the owner and the public, despite higher initial capital and O&M costs 10 (Portland BES, 2008). Not all benefits were examine d, but areas where economic benefits 11 accrued included : 12

• For the public: ( 1) Reduced Stormwater Quantity; ( 2) Avoided Stormwater Infrastructure; 13 ( 3) Improved Air Quality; ( 4) Enhanced Habitat 14

• For the owner or developer: ( 1) Reduced Stormwater Fees; ( 2) Extended Roof Life; 15 ( 3) Increased FAR allowance; ( 4) Reduced energy costs. 16 

### Example Green Roof Design Guides in the Chesapeake Bay Watershed 17 

### Area 18 US General Services Administration (GSA). 2009. Guideline Scope of Work, Design Build 19 Guidance Criteria Retrofitting Low-slope Roofs with a Vegetative Roof System. 20 Pennsylvania Department of Environmental Protection (PADEP). 2006. Pennsylvania 21 Stormwater Best Management Practices Manual, Docume nt Number: 363-0300-002, BMP 6.5.1: 22 Vegetative Roof. www.elibrary.dep.state.pa.us/dsweb/View/Collection- 8305 23 New York State Department of Environmental Conserva tion. New York State Stormwater 24 Management Design Manual, Draft Chapter 4.3.8 Green Roofs. December 2009. 25 Whole Building Design Guide. Extensive Green Roof Resources Page

. 26 www.wbdg.org/resources/greenroofs.php?r=site_potent ial#rcas 27


### References 28 ASTM International. 2006. Standard Guide for Select ion, Installation and Maintenance of Plants 29 for Green Roof Systems. Standard E2400-06. ASTM Int ernational. West Conshohocken, 30 PA . <http:// , available Online: www.astm.org/Standards/ E2400.htm >

. 31 Berhage, R., A. Jarrett, D. Beattie and others. 200 7. Quantifying evaporation and transpiration 32 water losses from green roofs and green roof media capacity for neutralizing acid rain

. 33 Final Report. National Decentralized Water Resource Capacity Development Project 34 Research Project. Pennsylvania State University. 353/15/20 2

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Chapter 3. Controlling Urban Runoff 168 Clark, S., B. Long, C. Siu, J. Spicher and K. Steel e. 2008. Early-life runoff quality: green versus 1 traditional roofs . Low Impact Development 2008. Seattle, WA. America n Society of Civil 2 Engineers. 3 Dietz, M.E . 2007. , Low-Impact Development Practices: A Review of Curr ent Research and 4 Recommendations for Future Directions, Water, Air, Soil Pollution, 186; 351-363 , 2007

. 5 Dunnett, N. and N. Kingsbury. 2004. Planting Green Roofs and Living Walls . Timber Press. 6 Portland, Oregon. 7 Glass, Charles C

. ., et al . 2007. Green Roof Water Quality and Quantity Monitoring , Howard 8 University Department of Civil Engineering, Univers ity Park, MD. 9 Green Roofs for Healthy Cities ( www.greenroofs.org ) 10 International Green Roofs Projects Database ( www.greenroofs.com ) 11 MDE ( Maryland Department of Environment . (MDE ). 2008. Chapter 5. Environmental Site 12 Design. Green Roofs. 13 Moran, A., W. Hunt and G. Jennings. 2004. Greenroof research of stormwater runoff quantity 14 and quality in North Carolina . NWQEP Notes. No. 114. North Carolina State Univer sity. 15 Raleigh, NC. 16 North Carolina State University (NCSU). 2008. Green Roof Research Web Page. Department of 17 Biological and Agricultural Engineering. www.bae.ncsu.edu/greenroofs

. 18 Portland BES ( Bureau of Environmental Services ). 2008 (BES)

. Cost Benefit Evaluation of 19 Ecoroofs, City of Portland, Oregon

. 20 , April 2008 21 Snodgrass, E. , and L. Snodgrass. 2006. Green Roof Plants: a resource and planting guide

. 22 Timber Press. Portland, OR. 23
U SEPA (U .S. Environmental Protection Agency ) , 2009

. , Green Roofs for Stormwater Control , 24 EPA/600/R-09/026. www.epa.gov/nrmrl/pubs/600r09026/600r09026.pdf

. 25 Van Woert, N., D. Rowe, A. Andersen, C. Rugh, T. Fe rnandez and L. Xiao. 2005. Green roof 26 stormwater retention: effects of roof surface, slop e, and media depth. Journal of 27 Environmental Quality

. 34: 1036

– - 1044. 28 Weiler, S. and K. Scholz-Barth 2009. Green Roof Systems: A Guide to the Planning, Design , and 29 Construction of Landscapes over Structure . Wiley Press , . New York, NY. 30 Water Environment Research Federation . 2009. , User’s Guide to the BMP and LID Whole Life 31 Cost Model, Version 2.0 , 2009

. 323/15/20 2

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Chapter 3. Controlling Urban Runoff 169 

### 6.4 Blue Roofs 1 

### Description of Practice 2 A blue roof is a roof design that is explicitly int ended to provide temporary storage and slow 3 release of stormwater runoff. In many locations, th ese approaches are also referred to as “ rooftop 4 detention ” . They are most commonly used in dense urban areas where other methods of 5 stormwater detention are impractical. Blue roofs ar e used to detain rooftop runoff onsite and 6 reduce the rate of runoff from rooftops during rain fall events. A blue roof may be used as a 7 standalone detention method, or because they do lit tle to improve the water quality of runoff, as 8 part of a treatment train that includes other low i mpact development and conventional best 9 management practices (BMPs) such as bioretention, i nfiltration, wetland systems, or green roofs 10 to enhance the function, improve the performance, a nd reduce the cost of those approaches. Blue 11 roofs are one of the least expensive means for temp orarily detaining stormwater on site and can 12 be used where green roofs are not feasible, cost ef fective or otherwise desired due to competing 13 needs. 14 The four primary blue roof types are described belo w: 15

• Roof-integrated Designs

— - Roof-integrated designs are built during new constr uction or 16 as modifications of existing roofs to intentionally store standing water over extended 17 periods. 18 19 These designs utilize a roofing membrane or waterpr oofing system as the primary water 20 detention structure. Therefore water is temporarily ponded directly on the roof surface. 21 Roof integrated designs can be designed to store wa ter as an open water surface or 22 partially or completely within a porous media. 23 24 In addition, structures such as walkways, decks, or plazas can be constructed on top of 25 roof integrated designs to minimize the impact of p onded water on roof access. 26 Alternatively, porous media such as flexible paving tiles or granular media can be used as 27 a permeable walking surface on all or part of the r oof to allow for access, while reducing 28 the amount of standing open water. 29 30 Roof-integrated designs can be constructed as a sec ondary roofing layer on top of an 31 existing surface in the same manner as a physical r oot barrier in green roof designs. 32 33

• Modular Tray Designs

— - Modular tray systems utilize plastic trays to tempo rarily 34 detain water during rainfall events and release thi s water over some period of time 35 following a rainfall event. This approach provides flexibility in both the size and 36 configuration of the detention system and is, there fore, well-suited for retrofit designs. 37 Equipment and other roof penetrations can be avoide d through selective placement of the 38 trays. Loading issues can be addressed though optim al density and placement 39 configurations. The trays can be physically attache d to the roof or underlying supporting 40 grid and/or held in place with ballast composed comprised of coarse stone or other 413/15/20 2

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Chapter 3. Controlling Urban Runoff 170 weighed materials. The depth of the ballast or medi a contained in the trays can be varied 1 depending on the desire to reduce the presence of o pen water surfaces. 2 3 Modular trays can have any number of different outl et designs according to the goals of 4 the installation (e.g., reduce peak flows, achieve specific lag time for target events, etc.). 5 When the water is released, the drainage system for the existing roof continues to 6 function as it did prior to the retrofit (i.e., hyd raulic head and flow depths on the roofing 7 surface during rainfall are not increased). 8 9 Modular tray blue roof designs can be selectively m ixed with green roof components to 10 improve aesthetics and provide some of the addition al benefits of green roofs. 11 The most challenging component of blue roof tray de signs is the robustness of the 12 hydraulic outlet design. Consistent and reliable dr ainage of the trays with little 13 maintenance is a key consideration. Some designs al low for trays to be interconnected to 14 effectively act as a larger “ tank ”

. 15 16

• Roof-Dams/Roof-Checks

— - Roof-dams or roof-checks effectively are impermeabl e or 17 semi-permeable interim breaks in the surface flow p aths installed on existing or new 18 roofs that allow water to pond behind them as tempo rary detention. The dams can 19 incorporate specific overflow or outlet designs to slowly release the stored water. In the 20 same manner as a roof-integrated design, the roof i s utilized as the primary water 21 detention structure with the flows being restricted by the roof-dams. If retrofit onto 22 existing roofs, the ability of the roof to accept a dditional ponding should be assessed and 23 addressed. In older roof installations new roofing and additional water proofing may need 24 to be installed in conjunction with the installatio n of the dams. 25 26

• Actively Controlled Systems

— – Blue roofs that are used for temporary rooftop stor age 27 can be classified as " active " or " passive " depending on the types of control devices used 28 to regulate drainage of water from the roof. Passiv e designs use hydraulic structures such 29 as weirs, orifice plates or hydraulic regulators to control release rates from the roof. 30 Active approaches allow for the use of a valve conf iguration and controller to regulate 31 discharge of flows from rooftops. 32 33 The simplest design for an actively controlled blue roof is the retrofit or installation of a 34 pneumatically or hydraulically actuated pinch valve on the roof leader drain pipe. This 35 valve can be connected to a low cost micro-controll er, which monitors hydraulic head on 36 the valve and timing of storage on the roof surface . The controller can be programmed to 37 release the ponded water according to some predeter mined optimal approach based on 38 analysis of the receiving storm sewer, downstream B MP, or receiving water. More 39 complex designs can integrate communications with s erver-side and/or internet based 40 data feeds, or telemetry to optimize release timing and quantities. 41 42 Blue roofs can be implemented effectively on shallo wly sloped roofs in residential, 43 manufacturing, commercial or industrial settings. R ooftop detention is a particularly good 443/15/20 2

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Chapter 3. Controlling Urban Runoff 171 storage option in densely developed areas where roo fs make up a significant portion of the total 1 site area. 2 Blue roofs are well-suited to applications on comme rcial and residential buildings, which 3 typically have large, flat roofs and little or no a rea available for storage on site surrounding the 4 building. Such large roofs generate significant run off quantities. Rooftop detention using blue 5 roofs represents a cost effective and convenient st orage option that can be applied to new 6 construction in the urban environment to provide ad equate storage volume and runoff reduction 7 to comply with stormwater regulations. 8 In addition to applications in densely developed ar eas, blue roof storage techniques also lend 9 themselves well to implementation on sites with mod erate to large flat roofs where flow from 10 impervious non-roof area (e.g. parking lots, walkwa ys, etc.) also contributes to the total runoff. 11 In these situations, blue roofs are used to control rooftop runoff, while subsurface BMPs are used 12 to control runoff from non-roof areas. The use of r ooftop storage on such sites reduces the 13 required volume for subsurface systems and allows t hese systems to be constructed over a 14 smaller area. 15 Key advantages include : 16

• Often the least expensive means for temporarily sto ring storm water at a site particularly 17 when compared to subsurface storage or green roof s ystems. 18

• Can reduce the size and/or improve the performance of downstream BMPs, such as 19 bioretention cells of infiltration systems. 20

• Easy to install – no additional excavation/construc tion required. 21

• Existing commercially available products for flow c ontrol. 22

• Readily coupled with other storage techniques, such as subsurface or surface storage. 23


### Hydrologic Performance and Targeted Pollutants 24 Hydrologic Performance 25

**Volume Reduction Peak Flow Reduction Groundwater Re charge**     Key:  High effectiveness  Medium effectiveness  Low effectiveness 26 Targeted Pollutants 27 **Sediment Nitrogen Phosphorus Metals Oil & Grease Ba cteria Temperature** 

       Key:  High effectiveness  Medium effectiveness  Low effectiveness3/15/20 2

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Chapter 3. Controlling Urban Runoff 172 

### Common Feasibility Constraints and Limitations 1

• Storage using outlet controls limited to flat roofs or roofs with shallow slopes (e.g., < 1 2 percent) due to increased ratio of ponding depth to available volume for steeper slopes. 3 This problem can be addressed through the use of mo dular tray designs or roof-dams. 4

• Limited benefit on sites where roof area makes up o nly a small portion of total 5 impervious area. 6

• Regular maintenance varies by design, but is an imp ortant consideration. Verification of 7 system performance may be necessary. 8

• Potential tampering must be considered in design. 9

• Pest problems must be avoided through through prope r design and maintenance, e.g., 10 mosquitoes. 11

• Local building codes should be checked to ensure de signs are compliant. 12


### Photos and Diagrams 13

14 Figure 3-26. Rooftop detention being used to contro l runoff at a commercial property 15 Source: with permission from the New York City Depa rtment of Environmental Protection 16


### Common Feasibility Constraints and Limitations 17 Because blue roof designs generally hold less than four inches of ponded water on the roof for 18 times ranging from a few minutes to many hours, blu e roofs typically do not impact the 19 availability of roof space for other uses. 20 If such water ponding is incompatible with anticipa ted future uses of the roof, the blue roof may 21 be designed to occupy a portion of the roof area, l eaving additional roof space available for other 22 purposes. If structures and equipment are mounted t o the roof within the area intended for 23 ponding water, it may be necessary to provide addit ional waterproofing around the structure or 24 equipment or to elevate the equipment above the ant icipated maximum water depth to prevent 253/15/20 2

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Chapter 3. Controlling Urban Runoff 173 damage and provide access for maintenance. Where ro ofs are intended to be used as means of 1 egress or points of rescue for fire safety, walkway pavers should be provided to allow for safe 2 passage to fire escapes from the roof surface. Thes e pavers provide a dry walking surface to 3 allow for safe movement through ponded water. In ad dition, decks, walkways or pavers may be 4 incorporated into the design of a rooftop detention system to provide space on the rooftop for 5 passive recreational use. 6 The application of blue roof systems is most effect ive on roofs with a maximum slope of about 7 1/8 inch per foot (or 1 percent % slope) or those with drainage configurations that can safely 8 allow for the necessary volume detention. 9 To prevent clogging, the owner should inspect drain s and clear snow and ice as necessary after 10 winter precipitation events in accordance with esta blished maintenance procedures. As with 11 conventional flat roofs, maintenance procedures for blue roof systems include the removal of 12 accumulated snow prior to an anticipated rain event to prevent possible overloading. 13 Homeowners or building maintenance staff may remove snow from the blue roof using the same 14 removal methods used for conventional flat roofs. 15


### Runoff Volume and Pollutant Load Removal Estimates 16 Blue roofs primarily provide a means for temporaril y detaining water. Little direct impact on 17 water quality can be achieved through the use of bl ue roofs alone. Some evaporation will occur 18 in systems that detain water for extended periods. Evaporation rates on blue roofs approach pan 19 evaporation rates. Pan evaporation rates can be sig nificant under certain climatic conditions (e.g., 20 hot, windy, low humidity days). 21 

### Practice Design 22 Blue roofs are most often constructed on flat or sh allowly sloped roofs, but tray and roof dam 23 designs can be used on slopes in excess of 5 percent % . On roof integrated designs where the roof 24 is sloped, even very shallow slopes dramatically re duce detention capacity. Typically in retrofit 25 situations the roof is reconstructed as a part of b lue roof installation. With tray designs this may 26 not be necessary. The designer must pay close atten tion to roof system manufacturer’s 27 requirements to ensure that the roofing system and design are compatible with manufacturer’s 28 warrantees and with the blue roof design. 29


### Maintenance Considerations and Resources 30 Maintenance for most blue roof systems are similar to those required for typical flat roofing 31 drainage systems and involve occasional snow and ic e removal, regular inspection for debris 32 clogging inlets, and inspection and repair of the r oof. 33 

### Costs and factors affecting cost 34 Blue roofs are one of the least expensive means for temporarily detaining stormwater on site. 35 The marginal cost of adding a blue roof to new cons truction is typically less than $2 per gallon of 36 temporary storage where structural modifications to building design are not required (e.g., 373/15/20 2

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Chapter 3. Controlling Urban Runoff 174 designs take into account snow loads). As new appro aches (e.g., tray designs) gain wider 1 acceptance in the marketplace it is expected that b lue roof detention may drop below $1 per 2 gallon of temporary storage. 3


### References 4 City of Valparaiso, Indiana . 2004. , Stimson Drain Stormwater Management Study Phase II 5 Report, Appendix B, Rooftop Storage , 2004

. 6 www.valparaisoutilities.org/stormwater/ssph2/Stimso nDrain/Appendices/AppendixB/25% 7 20-%20rooftop%20storage%20040915.pdf 8 Georgia Stormwater Management Manual; Volume Two: T echnical Handbook, 2001. 9 www.georgiastormwater.com 10 Guidebook Of Best Management Practices For Michigan Watersheds, Reprinted October, 1998, 11 Roof Top Storage Pages RTS-1 And RTS-2 in Best Mana gement Practices For 12 Construction Sites, Urban Areas and Golf Courses. 13 www.michigan.gov/documents/deq/deq-wb-nps-Intro_250 601_7.pdf 14 Iowa Statewide Urban Design Standards Manual. 2009. www.iowasudas.org/design.cfm 15 Ontario Stormwater Management Planning & Design Man ual, 2003. 16 www.ene.gov.on.ca/envision/gp/4329eindex.htm 17 Pennsylvania Stormwater Best Management Practices M anual, BMP 6.8.2: Special Detention 18 Areas – Parking Lot, Rooftop. 19 www.stormwaterpa.org/assets/media/BMP_manual/chapte r_6/Chapter_6-8-2.pdf 203/15/20 2

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Chapter 3. Controlling Urban Runoff 175 

### 6.5 Bioretention/Biofiltration 1 

### Description of Practice 2 Bioretention cells are small-scale, vegetated, shal low depressions that are used to reduce runoff 3 volumes and pollutants through the process of soil filtration, interception, vegetative uptake, 4 biological processes, infiltration, retention and e vapotranspiration. Bioretention cells can be used 5 as stand alone systems or as part of a treatment tr ain. Bioretention cells are typically designed 6 with native soils and or/an engineered soil mix, an d plants that are selected to be tolerant of a 7 range of wet and dry conditions. In some cases site conditions or design goals may require the 8 use of gravel for additional volume retention or th e use of overflow devices. Where groundwater 9 recharge is required, bioretention can help protect the quality of infiltrated stormwater. 10 The use of soil based vegetated systems have distin ct advantages over the use of nonbiological 11 infiltration trenches or similar designs for the fo llowing reasons (Davis , et al

. ., 2009): 12

• Roots promote media permeability. 13

• Surface vegetation can be used to slow stormwater f lows and filter sediments. 14

• Roots support microbial populations needed for poll utant biodegradation. 15

• Phytoremediation uptakes and breaks down pollutants

. 16 It is recommended that, where feasible, designs use a variety of hardy native plants that are 17 adapted for both wet and dry soil conditions to ens ure long-term plant survival and vigor. If 18 native plants are not available, the use of nonnati ve, noninvasive species that typically do not 19 require fertilizer, irrigation or pest control exce pt at establishment is appropriate. 20 Bioretention cells can be used in a wide set of app lications in the built environment to manage 21 runoff from roofs, lawns, and streets and other imp ervious areas such as parking lots and 22 sidewalks. Bioretention practice typically fall in to the following categories: 23

• Residential rain gardens 24

• Tree boxes (common and expanded) and shrub bioreten tion cells 25

• Sidewalk or right of way planter boxes 26

• Parking lot islands 27

• Street curbs extensions and bump-outs. 28

• Wooded bioretention areas 29

• Bioretention swales 303/15/20 2

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Chapter 3. Controlling Urban Runoff 176 

### Hydrologic Performance and Targeted Pollutants 1 Hydrologic Performance For Design Storm Events 2

**Volume Reduction Peak Flow Reduction Groundwater Re charge**     Key:  High effectiveness  Medium effectiveness  Low effectiveness 3 Targeted Pollutants 4 **Sediment Nitrogen Phosphorus Metals Oil & Grease Ba cteria Temperature** 

       Key:  High  Medium  Low 5 

### Photos and Diagrams 6

7 Figure 3-27. Bioretention Cell for Street and Yard Drainage. 8 Source: Larry Coffman, Prince George’s County, Some rset Subdivision 93/15/20 2

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Chapter 3. Controlling Urban Runoff 177 1 Figure 3-28. An Urban Bioretention System Treats Si dewalk and Road Runoff. 2 Source: Abby Hall, US EPA 3

4

5 Figure 3-29. Typical Bioretention Cell Cross-Sectio n. Not to Scale. 6 Source: LID Center 7

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Chapter 3. Controlling Urban Runoff 178 1 Figure 3-30. Wooded Bioretention Can Increase Pollu tant Uptake And Requires Specific Design 2 Modifications for Tree Growth and Avoiding Engineer ing Conflicts 3 Source: Urban Watershed Forestry Manual, Part 2, CW P and USDA, 2006 4

5

6 73/15/20 2

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Chapter 3. Controlling Urban Runoff 179 1 Figure 3-31. Bioretention Swales With and Without U nderdrain. 2 Source: Seattle Public Utilities 3

4

Figure 3-32. Infiltration Planter Box. Source: Portland Bureau of Environmental Services

5 

### Common Feasibility Constraints and Limitations 6 Bioretention practices should not be used in some a pplications, including : 7

• slopes are greater than 20 percent 83/15/20 2

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Chapter 3. Controlling Urban Runoff 180 • “ hot spots ” that have a high potential for groundwater contami nation, e.g., gas station 1 runoff or areas where chemicals are stored or manag ed 2

• large drainage areas from impervious areas greater than 15,000 square feet (unless a 3 system of separate cells is used to manage the runo ff) 4

• areas of shallow bedrock or high water tables where infiltration is not feasible (note: 5 design modification may be used to compensate for t hese conditions where surface 6 retention is desired) 7

• applications that have high sediment loadings unles s use pretreatment systems and/or 8 increase maintenance 9 Stormwater infiltration can affect groundwater qual ity; however, the incidence of groundwater 10 contaminated to an unhealthy level from stormwater is low. Many factors contribute to the risk 11 (Clark, et al., 2009) 12


### Estimated Effectiveness for Runoff Volume and Pollu tant Load Reduction 13 Volume Reduction. Guidance manuals are referenced in this fact sheet , and by state and local 14 jurisdictions, that provide instruction on methods for calculating volume reduction based on 15 infiltration rates and storage volumes. Evapotransp iration also provides some volume reduction. 16 The following factors influence the annual stormwat er volume reduction achievable on a broader 17 level: 18

• Local climate and rainfall patterns. 19

• Local soil characteristics, including the soils und erlying the constructed bioretention cell. 20

• Local evapotranspiration rates driven by climate co nditions, vegetation type, and length 21 of growing season. 22

• Site conditions such as location in a sunny area or in deep shade 23

• Ratio of cell media volume to drainage area. Increa sing the volume of media relative to 24 the drainage area has been demonstrated to reduce o utflow. 25

• Use of underdrain versus infiltration to underlying soil 26

• Care during construction to ensure construction sit e erosion does not clog the system 27
Pollutant Reduction. Pollutant concentration reductions can be obtained in the bioretention 28 system to further reduce overall loading. Many fact ors associated with the pollutants, water, soil, 29 plants, microbes, and system design affect pollutan t removal performance. 30 For example, nutrient removal can be influenced by the following factors: 31

• the amount of organic material and the potential fo r the media to decay and leach 32 nutrients. 33

• the form of phosphorus or nitrogen as it enters the cell, and transforms in the cell. 34

• biological transformation of nutrients in the cell in microbial and plant processes 35

• cation exchange capacity and ability to sorb nutrie nts 363/15/20 2

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Chapter 3. Controlling Urban Runoff 181 • the presence of an anaerobic/saturated zone which i nfluences denitrification potential 1

• soil media composition and volume 2

• Plant species, community composition, size, coverag e and health 3 Phosphorus removal requires the use of a low phosph orus index soil mix with a high cation 4 exchange capacity (Li, et al., 2009). Layering of m edia targeted at specific pollutants may 5 enhance water quality benefits (Li, et al., 2009). 6 A summary of some pollutant specific removal inform ation is provided below (Davis, et al., 7 2009). 8

• Suspended Solids – Reductions can be as high as 99 percent. New fac ilities may export 9 TSS from the washout of fines in the media. 10

• Phosphorus – Reduction is highly variable, typically from 50 – 80 percent. Effluent 11 phosphorus at some locations has been higher than i nfluent concentrations, largely due to 12 high initial levels of soil phosphorus. 13

• Nitrogen – Because of the complex interactions of nitrogen species, total nitrogen 14 removal is difficult to achieve. Nitrogen removal m ay be increased with the use of a 15 higher percentage of organic matter in the soil mix (Hinman, et al., 2005), provided the 16 organic matter does not contain high nitrogen conce ntrations. Bioretention effectively 17 removes organic nitrogen in the media’s organic mat erial. Nitrate, however, is very 18 mobile, and only when the media remains saturated f or an extended period denitrification 19 is possible. 20

• Heavy Metals – Dissolved and particulate-bound metals are remov ed by filtration of 21 particulate metals and adsorption of dissolved spec ies in the mulch and bioretention 22 media. Metals have been shown to be primarily remov ed in the first 1 to 2 inches of the 23 surface mulch layer (Hinman, et al., 2005). 24

• Oil & Grease – Sorption of low concentrations of motor oil to o rganic material in the soil 25 mix have resulted in removal efficiencies of 96–99 percent. Native bacteria in the mulch 26 then biodegrade the hydrocarbons in a few days 27

• Chlorides – Bioretention does not treat chlorides and, where exposed to salting practices, 28 has been found to leach chlorides year round. 29

• Bacteria – Removals of bacteria have been monitored to be b etween 70 percent 30 (Hathaway and Hunt, 2008) and 91 percent, through p rocess that include filtration, 31 drying, and exposure to sunlight. 32 The reductions in mass loading of N and P achievabl e with bioretention have been shown to be 33 due to the decrease in runoff volume, not necessari ly decreases in concentration. Field tests have 34 shown considerable mass reductions to be achieved e ven when increases in concentrations occur 35 across the bioretention cell from nutrients contain ed in the media (Hunt, Jarrett, Smith, and 36 Sharkey, 2006). For this reason, a volume reduction performance goal is recommended. 37 Understanding the ranges of effluent concentrations observed, though, is valuable to evaluate 38 performance. 393/15/20 2

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Chapter 3. Controlling Urban Runoff 182 Typical influent and effluent concentration ranges

. The range of observed concentrations of 1 nutrients in stormwater runoff in the National Stor mwater Quality Database is provided in the 2 Table 3-48 , to give an indication of influent concentration r anges. 3 For effluent quality, the following are noted: 4

• Effluent concentration goals of the New York State Design Manual, Chapter 10 5 Enhanced Phosphorus Removal (Quigley, Strecker, Pit t, Karimipou, 2008) 6

– less than or equal to 0.1 mg/l TP 7

– less than equal to 0.06 mg/L dissolved phosphorus 8

• Reported effluent concentration results from field studies in the Mid-Atlantic (Davis, et. 9 al 2009) 10

– from 0.06 to 0.56 mg/l TP 11

– from 0.08 to 2.8 mg/l TN 12 Table 3-48. Selected Median Concentration of Nitrog en and Phosphorus Pollutants from Urban 13 Land Uses 14

NH3 (mg/L) N02+NO3

(mg/L) Nitrogen, Total

Kjeldahl (mg/L) Phosphorus, total (mg/L) Residential 0.32 0.6 1.4 0.3 Commercial 0.5 0.6 1.6 0.22 Industrial 0.5 0.73 1.4 0.26 Freeways 1.07 0.28 2 0.25 Open Space 0.18 0.59 0.74 0.31 Source: Pitt, R., A. Maestre, and R. Morquecho. 200 4. The National Stormwater Quality Database (NSQD, version 1.1). University of Alabama, Department of Civil an d Environmental Engineering, Tuscaloosa, AL. http://rpitt.eng.ua.edu/Research/ms4/Paper/Mainms4p aper.html . Updated February 16, 2004. Accessed February 3, 2 010. Cold weather performance. Bioretention can provide effective infiltration in cold weather. Dietz 15 and Clausen (2007) report that, despite measureable frost, 99 percent of runoff was either 16 evapotranspirated or infiltrated for bioretention i n Connecticut. The University of New 17 Hampshire reports similar favorable performance in winter conditions (Roseen, et al 2009), and 18 rapid thawing of bioretention media is reported whe n runoff enters. 19 

### Summaries of Volume and Pollutant Loading Reduction s Achievable 20 A wide range of performance results have been obser ved in field tests, and authors cite the 21 difficulty of using such data to prepare general pe rformance estimates (Dietz, 2007; Li and 22 Davis, 2009, Allen, et al, 2009). Volume reductions of from 75 percent to greater than 90 percent 23 on an annual average basis have been reported with bioretention (Geosyntec Consultants, Urban 24 Stormwater BMP Performance Monitoring, International Stormwater BMP Database, 25 WERF/ASCE/EPA, 2009); these values typically reflec t precipitation patterns of the study area 26 where most of the annual rainfall occurs in small e vents of approximately an inch depth or less. 273/15/20 2

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Chapter 3. Controlling Urban Runoff 183 For understanding and comparing performance results , estimates should be for an annual basis 1 using long-term, region-specific weather data for a specific design scenario. 2 A review of recent performance estimates provided in Table 3-49 leads to the following 3 observations (Simpson, et al

. 2009): 4

• The majority of the load reduction is from runoff r eduction, therefore reporting the runoff 5 reduction component is essential for understanding system performance (Center for 6 Watershed Protection and Chesapeake Stormwater Netw ork , 2008). 7

• Volume reduction can be a surrogate for, or approxi mate indicator of, the pollutant 8 removal achieved. 9

Table 3-49: Generalized Bioretention Performance Es timates for the Chesapeake Bay Area 10 Demonstrate that the Majority of the Load Reduction is from Runoff Reduction 11

12 Source: Chesapeake Bay Program, Tom Simpson, Sarah Weamert, et al., 2009 Notes:

• Soil classification (A, B, C, D) per USDA National Resource Conservation Service (NRCS) 13

• Event Mean Concentration-based Removal expressed a s Percent Reduction (PR) 14

• Mass Based Removal expressed as percent removal of total load by mass (TR) 15

• Nitrogen concentration reduction is low potentially because the (estimated at 10%). The solubility of nitrate, the 16 potential for organic nitrogen and ammonia to miner alize in the bioretention media to the nitrate form , and the 17 lack of anaerobic conditions , organic matter carbon source, and time needed for denitrification contribute to 18 nitrogen export. 19

• Assumptions included: 1) highly impervious urbaniz ed land use; 2) generalized for design criteria typ ical of Bay 20 area jurisdictions; 3) low phosphorus soil media; 4 ) for annual loading reduced from rain events up to 1” to 1.5” 21 depth. 22

• Total removal estimated by the calculation TR = RR + {(100-RR) * PR)}, rounded to a factor of 5. 23

• Authors caution that the estimates, based on limit ed data and generalized for simplicity, may not rep resent true 24 long-term performance throughout the watershed. Per formance is highly variable even under controlled 25 conditions. 26


### Practice Design 27 Several design considerations influence the overall performance of bioretention, including : 28

• The potential for clogging should be assessed and p retreatment, such as such as mulch, 29 should be provided if necessary. If grass swales ar e used, care should be taken to ensure 303/15/20 2

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Chapter 3. Controlling Urban Runoff 184 that sediment will not accumulate to point where it overtakes the vegetation and becomes 1 costly to remove. 2

• Well draining soils allow for rapid infiltration, b ut if the infiltration rate is too rapid, 3 nitrate may pass though without treatment. 4

• Soils with slow infiltration rates may decrease the overall stormwater volume retention. 5 Infiltration tests at the site should be performed to better estimate expected performance. 6 In these conditions, if a specified volume is to be retain the designer should consider 7 designing the subbase with gravel or other material s to retain the requisite volume. 8

• When conditions necessitate the use of underdrains the discharge rate should be as slow 9 as feasible to maximize infiltration. Overflows are preferred to maintain maximum 10 infiltration. Other options include positioning the discharge orifice on the sidewall above 11 the bottom of the invert. 12

• An impermeable liner, with an underdrain, may be us ed to prevent migration of 13 stormwater from the bioretention cell, if needed. T hese systems provide water quality 14 improvements because of the pollutant reductions av ailable from the vegetated system 15 and moderate volume reductions from evapotranspirat ion. 16


### Hydrology and Volume Reduction 17 Considerations in the hydrologic performance of bio retention design include (Li , et al

. ., 2009; 18 Davis , et al

. ., 2009): 19

• Underdrained systems display the poorest hydrologic performance. 20

• Adding an internal storage zone below the underdrai n improves performance, allowing 21 more time for infiltration, and potentially denitri fication. 22

• Reduced rates have been reported in colder months. 23

• Infiltration and evapotranspiration reduce discharg e volume by 50-90 percent % 24 depending up on system variables. 25



### Maintenance Considerations and Resources 26 Typical maintenance activities are as follows: 27

• Supplemental irrigation may be needed during the fi rst 2 to 3 years after planting. 28 Drought-tolerant species may need little additional water after this period, except during 29 prolonged drought, when supplemental irrigation may become necessary for plant 30 survival. 31

• Weeds should be removed by hand until vegetation is established. Although plants may 32 need pruning to maintain healthy growth, routine mo wing should not be required. Dead 33 or diseased plants should be removed and replaced. Mulch should be re-applied when 34 erosion is evident to maintain a 2-3 inch depth. 35

• Inspect at least two times per year for sediment bu ildup, trash removal, erosion, and to 36 evaluate the vegetation. Sediment should be removed in a manner that minimizes soil 373/15/20 2

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Chapter 3. Controlling Urban Runoff 185 disturbance if buildup reaches 25 percent of the po nding depth. Ensure pretreatment 1 devices, if used, are maintained. 2

• Some manuals recommend replacing the top few inches of bioretention media every few 3 years and/or when infiltration rates slow down too much. 4 

### Costs and factors affecting cost 5 Costs vary according to many factors including soil depth, plant selections, slope conditions and 6 the contractor’s familiarity with the practice. Typ ically costs are (WERF, User’s Guide to the 7 BMP and LID Whole Life Cost Model, Version 2.0 , and associated spreadsheets, 2009) : 8

• For residential raingardens: Between $6 per square foot (installed by the owner) to $16 9 per square foot of raingarden surface area (profess ional installed). 10

• For urban curb-contained bioretention, $16–29 per s quare foot, driven by the cost of 11 curbing and other urban-related infrastructure that may be used for conventional 12 landscaping. 13

• Bioretention cells often replace areas that would h ave been landscaped, so the life-cycle 14 cost can be less than the landscaped alternative. 15 Some factors influencing costs are : 16

• Material availability and transport 17

• Site conditions (e.g. traffic, utilities) 18

• Native soils, subgrade soils such as clay that resu lt in the need for underdrain or overflow 19 device 20

• Specific stormwater management requirements, such a s enhanced nutrient removal. 21

• The need for, and the type of, pretreatment 22

• Vegetation type and scale 23

• Soil medium specifications and availability 24

• Size of installation 25 The Prince George’s County Bioretention Manual (2007) and WERF’s BMP and LID Whole Life 26 Cost Model (2009) provide reported costs and templates to faci litate project cost estimation. 27 

### Example Bioretention Design Manuals in the Chesapea ke Bay Watershed 28 

### Area 29 Delaware Department of Environmental Resources and Environmental Control, Green 30 Technology: Standards, Specifications, and Details for BMPs , Sections 2.4 and 2.5, 2005. 31 Pennsylvania Stormwater Best Management Practices M anual , BMP 6.4.5 Rain 32 Garden/Bioretention, 2006. 333/15/20 2

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Chapter 3. Controlling Urban Runoff 186 Prince George’s County, Maryland, Bioretention Manual , Revised December 2007; and Low1 Impact Development Design Strategies: An Integrated Design Approach , EPA 841-B-00-003, 2 2000. 3 Prince George’s County, Maryland, Low-Impact Development Hydrologic Analysis , EPA 841-B4 00-002, 2000. 5 U.S Fish and Wildlife Service, Bayscapes , www.fws.gov/ChesapeakeBay/Bayscapes.htm 6 Virginia Department of Conservation and Recreation, Stormwater Design Specification No. 9: 7 Bioretention , 2009. 8


### References 9 Caltrans . 2002. , Draft Biofilter Pilot Phosphorus Investigation , 20 02

. 10 Center for Watershed Protection and Chesapeake Stor mwater Network . 2008. , Technical 11 Memorandum: The Runoff Reduction Method , 2008

. 12 Clark, Shirley; R. Pitt, R. 2009. Field Groundwater Contamination Potential from Infiltrati on of 13 Urban Stormwater Runoff. 14 Colwell, Shanti R., R.R. Horner, D. B. Booth. 2000. et al., Characterization of Performance 15 Predictors and Evaluation of Mowing Practices in Bi ofiltration Swales , Center for Urban 16 Water Resources Management, Seattle, WA , 2000

. 17 Davis, Allen P., W.F. Hunt, R.G. Traver, and M. Cla r . 2009. , Bioretention Technology: 18 Overview of Current Practice and Future Needs , Journal of Environmental Engineering, 19 vol. 135, no. 3, pp. 109-117, March 2009. 20 Davis, Allen P., M. Shokouhian, H. Sharma, C. Minami, D. Winogradoff . 2003. et al., Water 21 Quality Improvement Through Bioretention: Lead, Cop per, and Zinc Removal , Water 22 Environment Research, 75, 73-82, January/February 2 003. 23 Davis, Allen P., M. Shokouhian, H. Sharma, C. Minami.. 2006. et al., Water Quality 24 Improvement through Bioretention Media: Nitrogen an d Phosphorus Removal , Water 25 Environment Research, vol. 78, no. 3, pp. 284-293, March 2006. 26 DiBliasi, C., Houng Li, Allen P. Davis, Upal Ghosh . 2009. , Removal and Fate of Polycyclic 27 Aromatic Hydrocarbon Pollutants in an Urban Stormwa ter Bioretention Facility, 28 Environmental Science and Technology, 2009 , 43, 494–502. 29 Dietz, M.E., and J. C. Clausen . 2005. , A Field Evaluation of Rain Garden Flow and Pollutan t 30 Treatment , Water, Air, and Soil Pollution, vol. 167, pp.123- 138 , 2005

. 31 Dietz, M.E . 2007. , Low-Impact Development Practices: A Review of Curre nt Research and 32 Recommendations for Future Directions, Water, Air, Soil Pollution, 186; 351-363 , 2007

. 33 Hathaway, Jon M, and William Hunt

. , Urban Waterways: Removal of Pathogens in Stormwater , 34 North Carolina Cooperative Extension Urban Waterway s Series, AGW-588-16W. 353/15/20 2

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Chapter 3. Controlling Urban Runoff 187 Hinman, Curtis, et al . 2005. ., Low Impact Development Technical Guidance Manual f or Puget 1 Sound , Puget Sound Action Team, Washington State Univers ity Pierce County Extension , 2 May 2005

. 3 Hinman, Curtis . 2007. , Maintenance of Low Impact Development Facilities , Puget Sound Action 4 Team , 2007

. 5 Hon, G.E. et al . 2002. ., Sustainable Oil and Grease Removal from Stormwater Runoff Hotspots 6 using Bioretention , Paper for the 74 th Annual Conference and Exhibition of the 7 Pennsylvania Water Environment Association, State C ollege, PA , June 2002

. 8 Hsieh, Chi-hsu, A.P. Davis, and B.A. Needleman . 2007. , Nitrogen Removal from Urban 9 Stormwater Runoff Through Layered Bioretention Colu mns . Water Environment Research, 10 79(12), p.2404-2411 , 2007

. 11 Hsieh, Chi-hsu, and Allen P. Davis . 2005. , Evaluation and Optimization of Bioretention Media 12 for Treatment of Urban Storm Water Runoff , Journal of Environmental Engineering , vol. 13 131, no. 11, pp 1521-1531, November 2005. 14 Hunt, William F., and Nancy White . 2001. , Designing Rain Gardens (Bioretention Areas) , North 15 Carolina Cooperative Extension Service, 2001, available at: 16 www.engr.uga.edu/service/outreach/Stormwater%20BMP/ BioretentionOverview.pdf , 17 (accessed August 2007). 18 Hunt, William F., A. R. Jarrett, J. T. Smith, and L. J. Sharkey. 200 6. et al., Evaluating 19 Bioretention Hydrology and Nutrient Removal at Thre e Field Sites in North Carolina , 20 Journal of Irrigation and Drainage Engineering, pp. 600-608, November/December 2006. 21 Geosyntec Consultants (Quigley, Strecker), Robert P itt, Shohreh Karimipour . 2009. , New York 22 State Stormwater Design Management Design Manual, C hapter 10 Enhanced Phosphorus 23 Removal Standards, December 2009 Draft. 24 Geosyntec Consultants (Quigley, M, and Clary J., et . al) . 2009. Urban Stormwater BMP 25 Performance Monitoring, International Stormwater BMP Database, WERF/ASCE/EP A 26 and Partners , 2009

. www.bmpdatabase.org 27 Li, Houng and A.P. Davis . 2009. , Water Quality Improvement through Reductions of Pol lutant 28 Loads Using Bioretention , Journal of Environmental Engineering, vol. 135, n o. 8, pp. 567- 29 576, August 2009. 30 Li, Houng, L.J. Sharkey, W.F. Hunt, and A.P. Davis . 2009. , Mitigation of Impervious Surface 31 Hydrology Using Bioretention in North Carolina and Maryland , Journal of Hydrologic 32 Engineering, vol. 14, no. 4, pp. 407-415 , April 2009

. 33 Roseen, R.M., T.P Ballestero, J.J. Houle, P. Avella neda, J. Briggs, G. Fowler, and R. Wildey. 34 2009. Seasonal Performance Variations for Storm-Water Man agement Systems in Cold 35 Climate Conditions ASCE Journal of Environmental Engineering, 135(3): 128-137

. 2009. 363/15/20 2

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Chapter 3. Controlling Urban Runoff 188 Simpson, Tom W., and S.E. Weammert . 2008. , Infiltration and Filtration Practices: Definition 1 and Nutrient and Sediment Reduction Effectiveness E stimates, The Mid-Atlantic Water 2 Program at the University of Maryland , 2008

. 3 http://archive.chesapeakebay.net/pubs/bmp/Infiltrat ion_and_Filtration_Practices.pdf 4 Sun, X., and A. P. Davis . 2007. , Heavy Metal Fates in Laboratory Bioretention System s , 5 Chemosphere, vol. 66, pp. 1601-1609 , 2007

. 6 Tackett, Tracey, Bioretention Soil Specifications , available at: 7 http://depts.washington.edu/urbhort/html/education/ BioretentionSoilSpecs.pdf , (accessed 8 January 2010). 9 University of New Hampshire . 2006. , Low Impact Stormwater Management Project at the 10 University of New Hampshire: A Final Report to the New Hampshire Estuaries Project , 11 2006

. 12 U.S. Department of Agriculture and Center for Water shed Protection . 2006. , Urban Watershed 13 Forestry Manual, Part 2 , Conserving and Planting Trees at Development Sites , 2006

. 14 U.S. Environmental Protection Agency - Region 1 . 2008. , Stormwater Best Management 15 Practices (BMP) Performance Analysis , 2008

. 16 U.S. Environmental Protection Agency . 1999. , Stormwater Technology Fact Sheet: Bioretention , 17 EPA 832-F-99-012, Office of Water, Washington, D.C. , September 1999. 18 Washington State Department of Ecology, Evaluation of Emerging Stormwater Treatment 19 Technologies. 20 Water Environment Research Federation . 2007. , Critical Assessment of Stormwater Treatment 21 and Control Selection Issues , 2007

. 22 Water Environment Research Federation . 2009. , Flow Control and Water Quality Treatment 23 Performance of a Residential Low Impact Development Pilot Project in Western 24 Washington , 2009

. 25 Water Environment Research Federation . 2006. , Infiltration vs. Surface Water Discharge: 26 Guidance for Stormwater Managers , 2006

. 27 Water Environment Research Federation . 2009. , User’s Guide to the BMP and LID Whole Life 28 Cost Model, Version 2.0 , 2009

. 293/15/20 2

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Chapter 3. Controlling Urban Runoff 189 

### 6.6 Soil Restoration 1 

### Description of practice 2 Soil restoration techniques can be , applied after construction , is used to improve deeply till 3 compacted soils . The addition of compost can increase soil organic content, provide beneficial 4 bacteria

and fungi, and improve or restore soil water retention capacity and overall soil their 5 porosity by amending them with compost. Compost is aerobically decomposed organic waste 6 and a mending a soil with compost increases the soil’s permeability . The addition of soil 7 amendments can delay and water holding capacity. This delays and often reduce reduces the peak 8 stormwater run-off flow rate , and volume, and decrease decreases irrigation water requirements. 9 Amending soils will also reduce fertilizer and pest icide requirements. Soil restoration techniques 10 may also be used as part of a system to provide additional retention or infiltration capacity to 11 manage runoff from disconnected gutters to enhance the runoff reduction performance of 12 downspout disconnections , grass channels, filterstrips, and impervious areas. and filter strips 13 

### Volume/specific pollutants addressed 14 The primary water quality improvements which result from restoring soil through tillage and 15 compost amendments are increased infiltration and t he resultin g runoff reduction. 16 

### Development sector(s) in which it is applied 17 Compost amended soils are suitable for any pervious area where soils have been or will be 18 compacted by the grading and construction process. Compost amendments can be applied to the 19 entire pervious area of a development or be targete d in select areas of the site to enhance the 20 performance of runoff reduction practices. Some com mon design applications include : 21 Reduce runoff from compacted lawns and bare 22

• Enhance rooftop disconnections on poor soils 23

• Increase volume of runoff infiltrated from rooftops or other areas 24 Increase volume of runoff infiltrated reduction within a grass channel or 25

• Increase runoff reduction within a filter strip 26

• Increase volume of runoff reduced by a the function of a tree cluster or reforested area of 27 the site (VADCR, 2009). 28


### Hydrologic Performance and Targeted Pollutants 29 The primary water quality improvements which result from restoring soil through tillage and 30 compost amendments are increased infiltration and t he resulting reduction in runoff volumes. 31 Reducing runoff volume with compost generally reduc es pollutant transport and loading off site 32 (Faucette, et al, 2005; Faucette et al, 2007). 33
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Chapter 3. Controlling Urban Runoff 190 

### Photo/diagram 1

2 Figure 3-33. Soil Amendments (Source: VADCR Specifi cation No. 4) 3


### Common feasibility constraints and limitations 4 Compost amendments are not recommended where : 5

• Existing soils have high infiltration rates (e.g., HSG “ A and B ” soils), although compost 6 amendments may be needed at mass-graded B soils to maintain runoff reduction rates. 7

• The water table or bedrock is located within 1.5 fe et of the soil surface. 8

• Slopes exceed 10 percent, unless surface applied as a compost blank et %. 9

• Existing soils are saturated or seasonally wet 10

• The use of tillage with soil amendments They would harm roots of existing trees (stay 11 outside the tree drip line) 12

• The downhill slope runs toward an existing or propo sed building foundation 13

• The contributing impervious surface area exceeds th e surface area of the amended soils 14 (VADCR, 2009). 15
Selection In addition , in many situations, different types of the compost amendments should 16 occur based on the can adversely impact water quality objectives of the jurisdiction or the project. 17 Compost amendments should , therefore precautions must be formulated to not adversely affect 18 water quality taken . Properties such as nutrient content, soil moistur e holding capacity, metals 19 uptake capacity, shrink/swell, product maturity, pa thogen, residual chemical content and weed 20 seed content require a high level of scrutiny to in sure the appropriate amendments are being used 21 (Lenhart, 2007). 223/15/20 2

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Chapter 3. Controlling Urban Runoff 191 

### Runoff volume and pollutant load removal estimates 1 Balousek conducted research that demonstrated that One study concluded that compost2 amended, chisel-plowed, and deep-tilled plot treatm ents showed runoff reductions from 74 to 91 3 percent, compared to the control. Chisel-plowed and deep-tilled treatment showed cumulative 4 runoff reductions of 40 to 53 percent, compared to the control (Balousek, 2003). The runoff 5 reduction volume achieved by soil restoration depen ds on the site application and the pre6 construction hydrologic soil group (VADCR, 2009). 7 The use of compost amendments can reduce or elimina te However, while the need for 8 supplemental continuous fertilization from inorganic fertilizer sources. Some t o establish and 9 maintain the turf is reduced, if not elimi nated, at compost

- amended sites, studies , however, 10 show that the concentrations of many pollutants can increase in the surface runoff after soils are 11 amended amending with compost , hence the need for specification standards where nutrient 12 runoff is to be limited . A study conducted by the USEPA ORD (Pitt et al, 1 999) found that 13 surface runoff from the compost-amended soils had g reater concentrations of almost all 14 constituents, compared to the surface runoff from t he control sites. The concentration increases 15 in the surface runoff and subsurface flows from the compost-amended soil test site were quite 16 large, typically in the range of 5 to 10 times grea ter. Subsurface flow concentration increases for 17 the compost-amended soil test sites were also commo n and about as large. When the decreased 18 surface flow quantities were considered in conjunct ion with the increased surface runoff 19 concentrations, it was found that all of the surfac e runoff mass discharges were reduced by large 20 amounts (to 2 to 50 percent of the unamended discha rges). However, many of the subsurface 21 flow mass discharges are expected to increase, espe cially for ammonia, phosphate, total 22 phosphorus, nitrates, and total nitrogen. The large phosphorus and nitrogen compound 23 concentrations found in surface runoff and subsurfa ce flows at the compost-amended soil sites 24 decreased significantly during the time of the test s (about 6 months). The older test sites also had 25 lower nutrient concentrations than the new sites, b ut still had elevated concentrations when 26 compared to the soil-only test plots. 27 Use of compost and soil amendments with quality con trol specifications will help avoid potential 28 issues such as excess nutrient runoff. 29 The quality type of compost is being used (i.e. feed stock, maturit y, presence of pesticides and 30 herbicides) must be considered to minimize the adve rse effects of water quality. One recent 31 study concluded that due to its high nutrient conte nt, but low leaching properties, mature 32 compost made from deciduous leaves makes suitable c ompost for soil amendment in applications 33 for water quality (Lenhart, 2007). Two studies conducted at the University of Georgia found that 34 when quality compost was used and compared to conve ntional seeding and mulching 35 applications, runoff nitrogen loading was reduced b y 58-92% and runoff phosphorus loading was 36 reduced by 83%-97% (Faucette, et al, 2005: Faucette , et al, 2007). 37 

### Practice design 38

• The depth of compost amendment is based on the rela tionship between the surface area of 39 the soil amendment to the contributing area of impe rvious cover that it receives. VADCR 40 Stormwater Design Specification No. 4 ( www.chesapeakestormwater.net/storage/ 41 first-draft-baywide-design-specificationsi/BAYWIDE% 20No%204%20SOIL 423/15/20 2

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Chapter 3. Controlling Urban Runoff 192 %20AMENDMENT%20SPECIFICATION.pdf ) includes a table (Table 3) which 1 provides guidance as to the depth of compost, incor poration depth, and incorporation type 2 based on the area to be amended and the contributin g impervious area. 3

• USEPA’s Compost Blanket Factsheet includes T o maximize the benefits of compost 4 addition, these guidelines set an amended so il organic content goal of between eight and 5 specifications for compost blankets for constructio n thirteen percent, by weight. As a 6 general rule of thumb this goal can be achieved by incorporating two units of loose soil 7 with one unit of loose compost (a 2: 1 ratio). Final depth of amended soil will be betwe en 8 eight and post-construction use. 9 (http://cfpub.epa.gov/npdes/stormwater/menuofbmps/i ndex.cfm?action=factsheet_results 10 &view=specific&bmp=118. 11 ten inches, dependent upon the equipment used. ( Chollak and Rosenfeld , 1998) 12

• The compost material should be well composted, free of viable weed seeds, and stable 13 with regard to oxygen consumption and carbon dioxid e generation. The compost 14 should shall have a moisture content that has no visible free w ater or dust produced when 15 handling the material. VADCR Stormwater Design Spec ification No. 4 16 ( www.chesapeakestormwater.net/storage/first-draft-ba ywide-design17 specificationsi/BAYWIDE%20No%204%20SOIL%20AMENDMENT %20SPECIFICAT 18 ION.pdf

) and the Low Impact Development Center 19 ( www.lowimpactdevelopment.org/epa03/saspec_print.htm ) provide technical 20 specifications for the compost material. 21

• Soil tests should be conducted are required during two stages of the compost amendment 22 process. The first testing is done to ascertain pre -construction soil properties at proposed 23 amendment areas. The second soil analysis is taken to determine whether any further 24 nutritional requirements, pH, and organic matter ad justments are necessary for plant 25 growth. 26 VADCR Stormwater Design Specification No. 4 27 ( www.chesapeakestormwater.net/storage/first-draft-ba ywide-design28 specificationsi/BAYWIDE%20No%204%20SOIL%20AMENDMENT %20SPECIFICATION.p 29 df ) includes design criteria for soil amendments used to enhance downspout disconnections, 30 grass channels, vegetated filter strips, in additio n to several Bay-specific regional design 31 variations. 32 The City of Redmond, Washington Guidelines for Land scaping with Compost-Amended Soils 33 ( www.redmond.gov/insidecityhall/publicworks/environm ent/pdfs/compostamendedsoils.pdf ) 34 (Chollak and Rosenfeld, 1998) provides detailed justification, design specifications and cost35 benefit analysis of using compost-amended soils. 36 The Composting Council and the Clean Washington Cou ncil developed guidance (Development 37 of a Landscape Architect Specification for Compost Utilization, 38 www.cwc.org/organics/org972rpt.pdf ) which contains a series of short and long compost use 39 specifications for various landscape applications. Both product specifications and end use 40 instructions are provided. 413/15/20 2

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Chapter 3. Controlling Urban Runoff 193 

### Maintenance considerations and resources 1 VADCR recommends specific practices be used during the first year after amendment to help 2 ensure success where turf is the appropriate ground cover. The establishment of other landscape 3 cover types, such as forest cover or native plantin gs, may require fewer or no follow-up chemical 4 inputs after the site has been stabilized. VADCR re commendations for turf are: 5 Successful soil compost amendments require certain tasks be undertaken in the first year. 6

• Initial inspections: For the first six months follo wing amendments, the site should be 7 inspected at least once after each storm event that exceeds a half- inch. 8

• Spot Reseeding: Inspectors should look for bare or eroding areas in the contributing 9 drainage area or around the soil restoration area, and make sure they are immediately 10 stabilized with grass cover. 11

• Fertilization: Depending on the amended soils test, a one-time, spot fertilization may be 12 needed in the fall after the first growing season t o increase plant vigor. 13

• Watering: Water once every three days for first mon th, and then weekly during first year 14 (Apr – Oct), depending on rainfall. (VADCR) 15
Item Unit Estimated unit cost (2005 Dollars) Soil and site preparation S.Y. $5 - $8 Mechanical grading and tilling S.Y. $18 - $27 Soil amendments C.Y. $15 - $30 Blower application S.Y. $0.45 - $1.00 16 

### Costs and factors affecting cost 17 Costs include the amendment and the application int o the existing soil. Typical costs are 18 provided below (http://www.lowimpactdevelopment.org /ffxcty/5-1_soilamendments_draft.pdf): 19
Item Unit Estimated unit cost (2005 Dollars) Soil and site preparation S.Y. $5 - $8 Mechanical grading and tilling S.Y. $18 - $27 Soil amendments C.Y. $15 - $30 Blower application S.Y. $0.45 - $1.00 20 Cost calculations based on amending soils on 1⁄4 acre area to manage runoff for a 1⁄2 acre area 21 were prepared by the Low Impact Development Center for Fairfax County, Virginia, in 2005, as 22 follows: 23 Required Cost per Year (2005 Dollars) Item 0 1 2 3 4 5 6 7 8 9 10

... 25 Installation 25,000 Aerate 250 250 250 250 2503/15/20 2

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Chapter 3. Controlling Urban Runoff 194 Re-amend 25,000 Total cost 25,000 250 250 250 250 250 25,000 Annualized Cost $1,125/year (includes re-amending in year 25)

1 Enhancement of existing soil with well compo sted material derived from yard debris compost or 2 biosolid amendment to form a Tilled Compost

- Amended Turf (TCT) will have higher soil 3 preparation costs than that of Topsoil Amended Turf (TAT) 1 or Minimum Input Turf

(MIT) 2 4 procedures (MIT is the most commo n procedure used in residential and commercial 5 development) . TCT practices will require a larger volume of mat erial to be delivered to the site 6 and more extensive site preparation procedures to e nsure the amendment is well mixed with the 7 existing soil. Add itional soil analyses will be required to determine the optimum quantities of the 8 various soil amendments. 9 However, turf grown on compost

- amended soil can save homeowners, residences, and 10 businesses money on water and fertilizer when compa red to the other types of turf. A study 11 conducted by the City of Redmond, Washington found that turf grown on tilled compost

12 amended soil by hydroseed application pays for itse lf: 13 1) Between the fifth and sixth year when compared t o topsoil

- seed, 14 2) During the first year w hen compared to topsoil

- sod, 15 3) Between the sixth and seventh year when compared to minimum

- seed, and 16 4) Between the second and third year when compared to minimum

- sod ( Chollak and Rosenfeld , 17 1998). 18


### References 19 Balousek. 2003. Quantifying decreases in stormwater runoff from dee p-tilling, chisel-planting 20 and compost amendments . Dane County Land Conservation Department. Madison , 21 Wisconsin. 22 Chollak, T. and P. Rosenfeld. 1998. Guidelines for Landscaping with Compost-Amended Soi ls

. 23 City of Redmond Public Works. 24 www.ci.redmond.wa.us/insidecityhall/publicworks/env ironment/pdfs/compostamendedsoil 25 s.pdf 26

1 The Topsoil Amended Turf method consists of the fo llowing: scarification of subsoil and rock removal, importation and even distribution of additional top soil, fertilizer and lime application, integration of so il layers by rototilling, grading and rolling of soil, seed, sod , or hydroseeding application.

2 The Minimum Input Turf soil preparation consists o f some rock removal and grading, even distribution of imported topsoil, fertilizer and lime application, grad ing and rolling of the soil, seed, sod or hydroseed ing application.3/15/20 2

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Chapter 3. Controlling Urban Runoff 195 Clean Washington Council and Composting Council

. , 1997. Development of a landscape 1 architect specification for compost utilization . Seattle, WA and Bethesda, MD. Prepared 2 by: E&A Environmental Consultants. www.cwc.org/organics/org972rpt.pdf 3 Faucette, L. B., J. Governo, C.F. Jordan, B. G Lockaby, H. F. Carino , and R. Governo. 2007. 4 Erosion control and storm water quality from straw with pam, mulch, and compost 5 blankets of varying particle sizes

. Journal of Soil and Water Conservation. 62:6: 404-4 13. 6 Faucette B, C. Jordan, M. Risse, M. Cabrera, D. Col eman, and L. West. 2005. Evaluation of 7 storm water from compost and conventional erosion c ontrol practices in construction 8 activities . Journal of Soil and Water Conservation. 60:6: 288 -297. 9 Pitt, R. J. Lantrip and R. Harrison. 1999. Infiltration through disturbed urban soils and comp ost10 amended soil effects on runoff quality and quantity . Research Report EPA/600/R-00/016. 11 Office of Research and Development. U.S. EPA. Washi ngton, D.C. 12 Lenhart, J. 2007. Compost as a soil amendment for water quality treat ment facilities

. 13 Proceedings 2007 LID Conference. Wilmington, NC 14 Low Impact Development Center. Guideline for Soil Amendments

. 15 www.lowimpactdevelopment.org/epa03/soilamend.htm 16 VA Department of Conservation and Recreation (VADCR ), 2009. Draft VA DCR Stormwater 17 Design Specification No. 4 – Soil Compost Amendment Version 1.5. July 2, 2009. 18 www.chesapeakestormwater.net/storage/first-draft-ba ywide-design19 specificationsi/BAYWIDE%20No%204%20SOIL%20AMENDMENT %20SPECIFICATI 20 ON.pdf 213/15/20 2

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Chapter 3. Controlling Urban Runoff 196 

### 6.7 Reforestation, Urban Forestry 1 

### Description of Practice 2 Forests are the most beneficial land use to protect the water quality of the Chesapeake Bay 3 (USDA Forest Service , Urban Tree Canopy Goal Setting , 2006). Reforestation is the protection, 4 enhancement and expansion of tree canopy in urban a nd suburban areas, in yards, parks, along 5 streets, and public places. Urban forests provide s ignificant environmental benefits though 6 management of urban stormwater, but also provide mu ltiple other benefits such as increasing 7 property values, reduce energy costs for cooling in the summer, buffer wind and noise, improve 8 air quality, provide habitat for wildlife, and beau tify the landscape. In urban areas, trees provide 9 an important stormwater management function by inte rcepting rainfall that would otherwise run 10 off of paved surfaces and be transported into local waters though the storm drainage system, 11 picking up various pollutants along the way (CWP an d USFS, 2009). Trees also enhance 12 stormwater management by evapotranspirating large q uantities of stormwater, while the roots 13 help to reduce soil compaction, enabling more infil tration of stormwater. In general, trees 14 stabilize soils, reduce stormwater runoff, maintain the base flow of streams and filter nutrients 15 and sediment (CWP, 2007). 16 Reforestion can be achieved using many tools, such as developing an urban tree canopy (UTC) 17 goal for a site or community, and achieving this go al through the use of regulations, policies 18 and/or incentives to plant trees and help ensure co ntinued growth. 19

20 Figure 3-34. Urban Watershed Forestry Objectives, B y Goal 21 Source: Cappiella, K.,et. al . 2005. Urban Watershe d Forestry Manual. Part 1: Methods for Increasing F orest Cover in 22 a Watershed, USDA Forest Service, Newtown Square, P A. 23

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Chapter 3. Controlling Urban Runoff 197 

### Photo/diagram 1

2 Figure 3-35. Urban Tree Canopy (Source: CWP & USDA, 2009) 3


### Common Feasibility Constraints and Limitations 4

• Developers have little incentive to leave or restor e trees on development projects. 5

• Unless regulations or incentives are in place, prop erty owners may not protect existing or 6 plant additional trees. 7

• Utility corridor needs lead to tree losses and dama ge 8

• Human safety (Fire response and transportation proj ects) often require tree removal 9



### Runoff Volume and Pollutant Load Removal Estimates 10 On average, forests approximately 1/10 of the nitro gen to the Chesapeake Bay compared to 11 developed lands (1.7 lbs acre compared to 14.8 lbs/ acre). More specifically, riparian forests that 12 buffer streams significantly reduce the amount of e xcess nutrients that enter the water, 13 sometimes by as much as 30 to 90 percent (CBP, 2007 ). 14 Forested areas have less runoff than developed area s, as indicated by the smaller runoff 15 coefficient used when comparing to disturbed or imp ervious areas. 163/15/20 2

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Chapter 3. Controlling Urban Runoff 198 Table 3-50: Site Cover Runoff Coefficients (Source: Hirschman et al, 2008) 1 1 Soil Condition Runoff Coefficient Forest Cover 0.02 – 0.05 2, 3 Disturbed Soils/Managed Turf 0.15 – 0.252 ,4 Impervious Cover 0.95 Derived from research by Pitt et al (2005), Lichter and Lindsey (1994), Schueler (2001a), Schueler, (2 001b), Legg et al (1996), Pitt et al (1999), Schueler (1987) and C appiella et al (2005) Range dependent on original Hydrologic Soil Group ( HSG) Forest - A: 0.02 B: 0.03 C: 0.04 D: 0.05 Disturbed Soils - A: 0.15 B: 0.20 C: 0.22 D: 0.25

Research has shown that trees are the most effectiv e at reducing the runoff from small, more 2 frequent storms (CWP and USDA, 2009). 3 

### Practice Design 4 There are many local, regional and site-specific pr actices that can be implemented to conserve 5 existing urban forest and increase forest restorati on. Local and state governments can develop 6 policies or plans which incorporate urban forestry, encourage/require practices such as stream 7 buffers, and provide incentives for developers and property owners to conserve or restore urban 8 forests. The following resources will provide more information about these options. 9

• Guidelines for Developing and Evaluating Tree Ordin ances (International Society of 10 Arboriculture) - www.isa-arbor.com/publications/ordinance.aspx 11

• Protecting Water Resources with Higher Density Deve lopment (USEPA) - 12 www.epa.gov/dced/pdf/protect_water_higher_density.p df 13

• Forest Friendly Development (Alliance for the Chesa peake Bay) - 14 www.alliancechesbay.org/pubs/projects/deliverables- 145-8-2005.pdf 15 In addition, local governments can lead by example and invest in urban forestry themselves. For 16 example, the Philadelphia (PA) Water Department Off ice of Watersheds (see 17 www.phillyriverinfo.org/Programs/SubprogramMain.asp x?Id=TreeVitalize ) contends that “trees 18 are one of the most effective, least costly methods of storing and controlling stormwater runoff.” 19 The Office of Watersheds has already contributed to the planting of over 500 trees within the 20 City of Philadelphia and hopes to increase this num ber through its involvement with the regional 21 TreeVitalize Program (see www.treevitalize.net ). As part of this program, Office of Watersheds 22 will partner with the Fairmount Park Commission to receive $300,000 over a three year period to 23 plant up to 84 acres of forested riparian buffers t hroughout Philadelphia’s park system (PWD, 24 2009). 25 Federal Implementation of the Chesapeake Executive Council Directive on Forest Conservation 26 provides specific actions to help achieve the goals of urban forest conservation and restorations. 27 ( www.chesapeakebay.net/press_ec2007forests.aspx?menu item=20276 ) 28 An example of local leadership in reforestation is Baltimore County’s Growing Home Campaign. 29 Benefit information is provided, including links to American Forests “ Personal Climate Change 303/15/20 2

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Chapter 3. Controlling Urban Runoff 199 Calculator ” , and the National “national Tree Benefits Benefits’ calculator from Casey Trees, a 1 local non-profit. These tools help to educate the p ublic on the multiple benefits of trees. The 2 County provides financial incentives to plant trees through a public-private partnership with local 3 nurseries and tree retailers, as follows: 4

• The Growing Home Campaign includes an educational b rochure that provides concise 5 information for homeowners about planting urban tre es and a cash incentive in the form 6 of a $10 coupon. The brochure is distributed throug h public libraries, senior centers and 7 parks facilities, the County web site ( ( www.growinghome.info ), and citizen watershed 8 organizations. 9

• Citizens bring $10 tree coupons to any of 50 partic ipating nursery retailers in Baltimore 10 County and cooperating jurisdictions (Harford Count y and the City of Baltimore). The 11 retailers return coupons used for tree purchases to Baltimore County, which captures data 12 on tree planting locations and costs. The County th en reimburses retailers for $5 of their 13 $10 discount provided to citizens. 14

• The Growing Home Campaign has resulted in the purch ase and planting of some 5,600 15 trees by homeowners since 2006, with a total econom ic impact of >$500,000. Every 16 dollar of County coupon match, which comes from a c apital improvement program 17 project for stormwater retrofits, currently leverag es about $18 of private investment in the 18 urban tree canopy. 19 The Center for Watershed Protection ( www.cwp.org ) and the USDA Forest Service has 20 developed new designs for stormwater management pra ctices for use in incorporating functional 21 tree-based stormwater management systems into devel opments. These “ stormwater forestry 22 practices ” address potential limitations through design modif ications, species selection, and 23 other methods. The designs listed below harness the benefits of trees to increase the effectiveness 24 of stormwater practices, while providing other bene fits to the community, such as cooling and 25 shade, aesthetics, and wildlife habitat (CWP and US DA, 2009). The fact sheets listed below are 26 available at www.forestsforwatersheds.org/reduce-stormwater

. 27

• Wooded wetland 28

• Emergent pond/wetland system 29

• Bioretention and bioinfiltration facilities 30

• Alternating side slope plantings 31

• Tree check dams 32

• Forested filter strip 33

• Multi-zone filter strip 34

• Linear storm water tree pit 35

• Stormwater treatment dry ponds 36 Trees design in dense urban environments presents m any challenges with the infrastructure of 37 streets, sidewalks, and utilities. Resources for ad dressing these issues include Reducing 38 Infrastructure Damage by Tree Roots: A Compendium o f Strategies (Costello and Jones, 2003). 39 Other planning considerations such as neighborhood character in tree selection and placement 403/15/20 2

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Chapter 3. Controlling Urban Runoff 200 are essential for a successful community street tre e program ( The Road to a Thoughtful Street 1 Tree Master Plan: A Practical Guide to Systematic P lanning and Design, Simons and Johnson, 2 2008 ). 3 Practices to prevent root compaction and provide ad ditional space under pavements for tree root 4 growth are gaining acceptance. One example is Minne sota’s MARQ2 project that used an 5 elevated-pavement type structural support system fo r the planting of 179 trees along a 6 redeveloped streetscape in the downtown area. The s ystem was designed to manage stormwater 7 as one of its functions, to help prevent combined s ewer overflows 8 ( http://www.stormh2o.com/march-april-2010/reshaping- minneapolis9 project.aspxwww.ci.minneapolis.mn.us/public

- works/Marq2/about.asp ). 10 More information on using trees to manage stormwate r are can be found at : 11

• Urban Watershed Forestry Manual Part 2: Conserving and Planting Trees at 12 Development Sites - www.forestsforwatersheds.org/storage/part2forestrym anual.pdf 13

• Stormwater Management: Using Trees and Structural S oils to Improve Water Quality - 14 www.cnr.vt.edu/urbanforestry/stormwater 15

• Watershed Forestry Resource Guide – Reducing Stormw ater Runoff - 16 www.forestsforwatersheds.org/reduce-stormwater 17



### Maintenance Considerations and Resources 18 The benefits of urban trees can be extended with ap propriate selection, planting design, and 19 maintenance. American Forests estimates that the av erage life expectancy of a downtown urban 20 street tree is just 13 years, while their rural cou nterparts can live up to 100 years or more. 21 Symptoms of tree decline from urban stressors can t ake years to appear. Common causes of 22 urban tree mortality include : 23

• Damage to roots or soils from nearby construction a ctivities 24

• Air pollution 25

• Physical damage from lawnmowers, vehicles or vandal s 26

• Damage from disease and insects 27

• Trees planted in too small a space 28

• Improper planting and pruning techniques 29

• Tree stakes or grates left on too long 30

• Poor, compacted soils 31

• Lack of watering 32

• Removal or damage during maintenance of nearby util ities or sidewalks 33

• Competition from invasive plant species (CWP and US DA, 2009). 34 The Urban Watershed Forestry Manual Part 3: Urban T ree Planting Guide (CWP, 2006) 35 (available at www.forestsforwatersheds.org/storage/Part3ForestryM anual.pdf )provides detailed 363/15/20 2

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Chapter 3. Controlling Urban Runoff 201 guidance on urban tree planting, including site ass essment, planting design, site preparation, and 1 planting and maintenance techniques. 2 

### Costs and Factors Affecting Cost 3 The costs of reforestation will vary greatly based upon how and where the trees are incorporated 4 into the urban/suburban landscape. A recent source of information on program cost includes the 5 American Public Works Association urban forestry ha ndbook. This project was supported by the 6 USDA Forest Service Urban and Community Forestry Pr ogram on the recommendation of the 7 National Urban and Community Forestry Advisory Coun cil. The handbook series is titled Urban 8 Forestry Best Management Practices for Public Works Managers, and the individual handbooks 9 are : 10

• Volume 1 Budgeting and Funding 11

• Volume 2 Staffing 12

• Volume 3 Ordinances, Regulations, & Public Policies 13

• Volume 4 Urban Forest Management Plan 14
This series is available free for download at APWA Press, 15 www.apwa.net/About/CoopAgreements/urbanforestry

. 16 The cost-benefit of planting trees will also vary, however, and research is being done to attempt 17 to quantify the value of urban tree canopy. America n Forests ( www.americanforests.org ) has 18 developed a tool to calculate the value of urban tr ee canopy in metropolitan areas. For example, 19 American Forests determined that 34 percent % of Montgomery, Alabama was covered by tree 20 canopy in 2002. The stormwater retention capacity o f Montgomery’s urban forest is 227 million 21 ft 3 . The cost to manage this volume of runoff in tradi tional infrastructure is estimated at $454 22 million. In addition, Montgomery’s urban forest is estimated to remove 3.2 million lbs of 23 pollutants from the air annually and this benefit i s valued at $7.9 million (American Forests, 24 2004). Even in arid locations trees are important. In 2007, American Forests found that 25 Albuquerque, New Mexico’s tree canopy provided 20 m illion cubic feet in stormwater detention 26 services, valued at $123 million (American Forests, 2009). 27 Further, forests filter pollutants from runoff ther efore allowing fewer contaminants to reach 28 potable water sources. This results in less treatme nt costs for local governments. 293/15/20 2

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Chapter 3. Controlling Urban Runoff 202 1 Figure 3-36. Relationship between forest cover and water treatment costs. 2


### Practice/program evaluation 3 The USDA Forest Service provides a Guide for Chesap eake Bay Communities (see 4 www.jmorgangrove.net/Morgan/UTC-FOS_files/UTC_Guide _Final_DRAFT.pdf ) to assist them 5 with the setting and evaluation of urban tree canop y goals. Setting tree canopy goals is essential 6 to achieving program success. Principles of an effe ctive urban forest program and several case 7 studies across the United States are provided in th e US Forest Service-supported guide Planning 8 the Urban Forest: Ecology, Economy, and Community D evelopment (Schwab, American 9 Planning Association, 2009). 10


### References 11 American Forests

. , 2009. Urban Ecosystem Analysis Albuquerque, New Me xico: Calculating the 12 Value of Nature. www.americanforests.org/downloads/rea/Alb_5%2022.pd f 13 American Forests

. , 2004. Urban Ecosystem Analysis Montgomery, AL : Calculating the Value 14 of the Urban Forest. www.americanforests.org/downloads/rea/AF_Montgomery .pdf 15 Baltimore County, Maryland, Growing Home Campaign, 16 www.baltimorecountymd.gov/Agencies/environment/grow inghome/index.html 173/15/20 2

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Chapter 3. Controlling Urban Runoff 203 Cappiella, K., T. Schueler, and T. Wright. 2005. Urban Watershed Forestry Manual. Part 1: 1 Methods for Increasing Forest Cover in a Watershed. USDA Forest Service, Newtown 2 Square, PA. 3 Cappiella, K., T. Schueler, and T. Wright. 2005. Urban Watershed Forestry Manual. Part 2: 4 Conserving and Planting Trees at Development Sites . USDA Forest Service, Newtown 5 Square, PA. 6 Center for Watershed Protection (CWP) and the USDA U.S. Forest Service (USDA), 2009. 7 Webpage accessed on December 17, 2009. www.forestsforwatersheds.org 8 Chesapeake Bay Program, 2007. Chesapeake Bay Progra m Announces Forest Conservation 9 Goals for Watershed. Press Release. December 5, 200 7. 10 www.chesapeakebay.net/press_ec2007forests.aspx 11 Costello, L.R., and K.S. Jones, Reducing Infrastructure Damage by Tree Roots: A Com pendium 12 of Strategies, University of California Cooperative Extension, Pub lished by the Western 13 Chapter of the International Society of Arborcultur e. 14 Ernst, C., R. Gullick, and K. Nixon. 2004. Protecti ng the Source: Conserving Forests to Protect 15 Water. OpFlow . American Waterworks Association. Vol. 30, No. 5. 16 Forests for Watersheds, www.forestsforwatersheds.org 17 Hirschman, D., K. Collins, and T. Schueler, 2008. T echnical Memorandum: 18 The Runoff Reduction Method. Center for Watershed P rotection. 19 Legg, A. R. Bannerman and J. Panuska. 1996. Variati on in the relation of runoff from residential 20 lawns in Madison, Wisconsin. USGS Water Resources I nvestigations Report 96-4194. 21 Lichter J. and P. Lindsey. 1994. Soil compaction an d site construction: assessment and case 22 studies. The Landscape Below Ground. International Society of Arborculture 23 Pitt, R. S. Chen, S. Clark and J. Lantrip. 2005. So il structure effects associated with urbanization 24 and the benefits of soil amendments. World Water an d Environmental Resources Congress. 25 Conference Proceedings. American Society of Civil E ngineers. Anchorage, AK. 26 Pitt, R. J. Lantrip and R. Harrison. 1999. Infiltra tion through disturbed urban soils and compost27 amended soil effects on runoff quality and quantity . Research Report EPA/600/R-00/016. 28 Office of Research and Development. U.S. EPA. Washi ngton, D.C. 29 Philadelphia Water Department, 2009. TreeVitalize - Comprehensive Tree Planting Program. 30 www.phillyriverinfo.org/Programs/SubprogramMain.asp x?Id=TreeVitalize Website 31 accessed: December 18, 2009. 32 Schueler, T. 1987. Controlling urban runoff: a prac tical manual for planning and designing urban 33 best management practices. Metropolitan Washington Council of Governments. 34 Washington, DC. 353/15/20 2

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Chapter 3. Controlling Urban Runoff 204 Schueler, T. 2001a. The compaction of urban soils. Watershed Protection Techniques. 3(2): 661- 1 665. 2 Schueler, T. 2001b. Can urban soil compaction be re versed? Watershed Protection Techniques. 3 3(2): 666-669. 4 Schwab, James C., Editor . 2009. , Planning the Urban Forest: Ecology, Economy, and 5 Community Development. American Planning Association, Planning Advisory Se rvice, 6 Report Number 555 , January 2009

. 7 Simons, Ken, and Gary R. Johnson . 2008. , The Road to a Thoughtful Street Tree Master Plan: A 8 Practical Guide to Systematic Planning and Design, University of Minnesota , 2008

. 9 Stormwater Magazine, Editorial Project Profile, Reshaping Downtown Minneapolis. Stormwater 10 Magazine, March-April, 2010. http://www.stormh2o.co m/march-april-2010/reshaping11 minneapolis-project.aspx 12 USDA. 2002. Fact Sheet #4: Control Stormwater Runoff with Trees . Center for Urban Forest 13 Research, Pacific Southwest Research Station, Davis , California. July 2002. 14 USDA, Urban Tree Canopy Goal Setting – A Guide for the Ch esapeake Bay , Forest Service, 15 Northeastern Area, State and Private Forestry, Ches apeake Bay Program Office, Annapolis, 16 MD. 173/15/20 2

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Chapter 3. Controlling Urban Runoff 205 

### 6.8 Street Sweeping 1 

### Description of Practice 2 Street sweeping can provide significant pollutant r emoval, but many municipalities use sweepers 3 that do not perform effectively, or that can actual ly cause more water quality issues ( NURP, 4 Sutherland, Bannerman, Pitt 2004 ). Aesthetics is main reason most municipalities us e sweepers, 5 not water quality, and for this use “ mechanical ” broom sweepers can perform well. However, 6 they do not provide the level of water quality bene fit that can be obtained using improved 7 sweepers. 8 Streets and roads compose comprise up to 20 percent % of total impervious cover in suburban 9 subwatersheds and up to 40 percent % in highly urban subwatersheds. Contaminated partic ulates 10 or “ street dirt ” accumulates along curbed roads between rainfall ev ents. During intense rainfall 11 events additional particulates can be washed on to these paved surfaces from adjoining land 12 areas. This wet weather wash-on has been demonstrat ed to be quite important in understanding 13 the pollutant removal benefits of street sweeping ( Sutherland and Jelen 1996 ). Sources of 14 pollutants include wash-on, atmospheric deposition, vehicle emissions, cargo spills, and wear 15 and tear, breakup of street surface, road salts and deicers, litter, bird droppings, grass clippings, 16 leaves and other organic material and sanding. This results in the accumulation of stormwater 17 pollutants such as sediment, nutrients, metals, hyd rocarbons, bacteria, pesticides, trash and other 18 toxic chemicals (CWP 2008). 19 These pollutants typically remain on streets until they are washed into the storm drain system 20 during a rainfall event. However, some communities use street sweeping to remove some of 21 these pollutants and prevent them from being convey ed into the storm drain system (CWP 2008). 22 Street sweeping and vacuuming includes the use of s elf-propelled and walk-behind equipment to 23 remove sediment from streets and roadways, and to c lean paved surfaces in preparation for final 24 paving. Sweeping and vacuuming prevents sediment fr om entering storm drains or receiving 25 waters (CASQA 2003). 26 

### Targeted Pollutants (Highly Dependent on Equipment Type) 27 Targeted Pollutants 28 **Sediment Hydrocarbons Trash Nutrients**
       Key:  High effectiveness  Medium effectiveness  Low effectiveness3/15/20 2

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Chapter 3. Controlling Urban Runoff 206 

### Photos 1

2 Figure 3-37. The majority of pollutants on streets are closest to the curb 3 Source: www.quincyma.gov/Living 4


### Common Feasibility Constraints and Limitations 5 The following are common feasibility constraints an d limitations of street sweeping: 6

• Sweeping and vacuuming may not be effective when se diment is wet or when tracked 7 soil is caked (caked soil may need to be scraped lo ose) (CASQA 2003). 8

• Be careful not to sweep up any unknown substances o r any object that may be potentially 9 hazardous (CASQA 2003). 10

• The use of kick brooms or some sweeper attachments tend to spread dirt rather than 11 remove it (CASQA 2003). On the other hand, gutter b rooms can be very effective at 12 capturing street dirt. 13

• Access to the curb is paramount to street sweeping efficiency, as the majority of 14 pollutants on streets are closest to the curb. Park ed cars can restrict access. Compliance 15 with an appropriately enforced no-parking zone may provide access for street sweeping 16 to the curb (CWP 2008). 17



### Pollutant Load Removal Estimates 18 The ability of street sweepers to remove common sto rmwater pollutants varies depending on the 19 sweeper technology being used, climate factors such as rainfall patterns, sweeper operation 20 (including sweeper speed), sweeper maintenance (inc luding broom wear), sweeping frequency, 21 pavement conditions, the number of parked cars enco untered, and the chemical and physical 22 characteristics of the pollutants that have accumul ated on the pavement. In addition, it can be 23 difficult to estimate pollutant removal rates for s treet sweepers because of the difficulty in 24 measuring particulate matter transported in runoff (APWA 2009), 25 Pros and cons of sweeper type on pollutant removal performance : 26

• Mechanical street sweepers are more effective at re moving larger-sized particles than 27 fine-grained particles and nutrients. Newer high ef ficiency sweepers pick up much 28 smaller particles, as well (Sutherland and Jelen, 1 997; Pitt, Bannerman, and Sutherland, 29 2004). 303/15/20 2

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Chapter 3. Controlling Urban Runoff 207 • Mechanical sweepers are typically the least expensi ve and are better suited to pick up 1 trash and coarse-grained sediment particles (CWP 20 08). This provides less water quality 2 benefits, but this practice could be used as the fi rst pass of tandem sweeping operations 3 when followed by a sweeper that can remove the poll utant-heavy fine-sized particles left 4 behind by the mechanical sweeper. 5

• Regenerative air and high efficiency sweepers are b etter at removing fine-grained 6 sediment particles, but are less effective on wet s urfaces (although may still out-perform 7 mechanical sweepers) and are more expensive (CWP 20 08). 8

• Street sweeping is presumed to be more effective at reducing stormwater pollutants in 9 arid and semi-arid climates where pollutants can ac cumulate over longer intervals on 10 street and curb surfaces (CWP 2008). 11


### Practice Design 12

• Because they operate as a mobile BMP on-the-go, str eet sweeping may be of particular 13 value in reducing pollutants from ultra-urban areas where few BMPs are feasible (Law et 14 al. 2008). 15

• Street cleaning equipment can be most effective in areas where the surface to be cleaned 16 is the major source of contaminants. These areas in clude freeways, large commercial 17 parking lots, and paved storage areas (Pitt, Banner man, and Sutherland 2004). 18

• Improving or initiating street sweeping activities can reduce the amount of stormwater 19 pollution that is conveyed into local aquatic resou rces. It requires examination of existing 20 street sweeping technology and operations (if any) and identification of where 21 improvements can be made to reduce the amount of po llution that has accumulated on 22 public streets and roadways. (CWP 2008). 23

• Develop a list of areas where street sweeping activ ities could have the greatest influence 24 on water quality. For example, an area with high ac cumulations of pollutants may suggest 25 that more regularly scheduled street sweeping is ne eded. Also, street sweeping may be 26 concentrated on the dirtiest streets in sensitive s ubwatersheds (CWP 2008). 27

• At a minimum, sweeping should occur during periods of heavy accumulation, such as 28 early spring removal of deicing chemicals and sand in temperate climates (CWP 2008). 29 During the fall, leaf removal should be conducted w ith specialized equipment, such as 30 vactor trucks, as seasonal leaves can contribute 25 percent % of nutrient loading in catch 31 basins. 32

• Include municipal parking lots in the sweeping sche dule. 33 

### Costs and factors affecting cost 34 Several factors influence the overall cost of stree t sweeping: 35

• Street sweeping is major investment and operators m ust be specially trained on how to 36 properly drive and maintain them. Training should b e held at least once a year for staff to 37 provide them with a thorough understanding or the p roper implementation of sweeping 383/15/20 2

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Chapter 3. Controlling Urban Runoff 208 and other pollution prevention/good housekeeping pr actices, and safety procedures (CWP 1 2008). 2

• Costs can vary significantly based on the type of s weeper, operation and maintenance 3 expenses, and sweeping frequency. The capital cost for a conventional street sweeper is 4 between $60,000 and $120,000 with newer technologie s approaching $180,000 (CASQA 5 2003). 6

• Rental rates for self

- propelled sweepers vary depending on hopper size an d duration of 7 rental. Expect rental rates from $58/hour (3 yd 3 hopper) to $88/hour (9 yd 3 hopper), plus 8 operator costs. Hourly production rates vary with the amount of are a to be swept and 9 amount of sediment. Match hopper size to the area and expect ed sediment load to 10 minimize time spent dumping (CASQA 2003). 11 

### Practice/Program Evaluation 12 It is important to evaluate the process and measura ble performance goals and implementation 13 milestones made for a street sweeping program. 14 Table 3-51. Examples of measurable goals Measurable Goals and implementation 15 milestones Implementation Milestones for 16 improving municipal street sweeping activities Improving Municipal Street Sweeping Activities 1 17 (adapted from CWP 2008) 18 Example measurable goals Example Measurable Goals Time frame Priority Goals related to program startup Identify and collect basic information about munici pal street sweeping activities Essential
Add the information about street sweeping activitie s to the simple database or binder that contains basi c information about each municipal operation Essential

Develop a digital GIS or hard copy map showing the location of all municipal street sweeping activitie s Complete shortly after program startup; updated regularly after

that Optional but

Recommended Prioritize local pollution prevention/good housekeeping efforts Year 1, repeat every 5 years Essential

Goals related to preventing or reducing stormwater pollution Collect additional information about the way that street sweeping activities are conducted within you r community. Include sweeper type; efficiency of fine sediment fraction removed, sweeping frequency, miles swept/coverage, and parking policies and enforcement along sweeping routes. Essential

Prescribe pollution prevention/good housekeeping practices to improve the way that municipal street sweeping activities are conducted within your community Essential

Develop implementation plan for prescribed street sweeping program Year 1

Essential
Secure funding and resources to implement Begin in Year 1 Essential3/15/20 2

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Chapter 3. Controlling Urban Runoff 209 prescribed street sweeping program Implement prescribed street sweeping program Begin in Year 2 Essential Goals related to program evaluation Develop measurable performance goals and implementation milestones Essential
Evaluate progress in meeting measurable goals and implementation milestones, including pollution prevent/good housekeeping practices Complete shortly after program startup; updated regularly after

that Essential

1) These goals assume that street sweeping is at th e top of your prioritized municipal operations list

. 1 The methods used to evaluate success in meeting mea surable goals and implementation 2 milestones can be as simple as a semi-annual or ann ual inspections used to identify the 3 improvements that have been put in place and the im provements that still need to be made (CWP 4 2008). 5


### References 6 California Stormwater Quality Association (CASQA). 2003. California Stormwater BMP 7 Handbook, Construction. January 2003. 8 www.cabmphandbooks.com/Documents/Construction/SE-7. pdf 9 Center for Watershed Protection (CWP). 2008. Urban Subwatershed Restoration Manual 9: 10 Municipal Pollution Prevention/Good Housekeeping Pr actices. Verison 1. Ellicott City, 11 MD , September 2008

. www.cwp.org/Store/usrm.htm#9 12 Center for Watershed Protection (CWP). 2006. Technical Memorandum 1. Literature Review. 13 Research in Support of an Interim Pollutants Remova l Rate for Street Sweeping and Storm 14 Drain Cleanout Activities. Ellicott City, MD , 2006

. 15 Neely L. Law, et al . 2008. ., Deriving Reliable Pollutant Removal Rates for Munic ipal Street 16 Sweeping and Storm Drain Cleanout Programs in the C hesapeake Bay Basin . Center for 17 Watershed Protection, Ellicott City, MD , September 2008

. 18 www.cwp.org/Resource_Library/Restoration_and_Waters hed_Stewardship/municipal.htm 19 Sutherland, R.C. and Jelen, S.L. 1997. Contrary to Conventional Wisdom: Street Sweeping ca n 20 be and Effective BMP. In James, W. Advances in Modeling the Management o f 21 Stormwater Impacts, vol. 5. Published by CHI, Guelp h, Canada, pp 179-190 , 1997

. 22 Sutherland, R.C. 2009. Recent street sweeping pilot studies are flawed . IN: APWA Reporter, 23 September 2009. 24 Pitt, Robert ; : Roger Bannerman, and Roger Sutherland . 2004. ; The Role of Street Cleaning in 25 Stormwater Management, Water World and Environmenta l Resources Conference 2004 , 26 Environmental and Water Resources Institute of the American Society of Civil Engineers, 27 Salt Lake City, Utah. May 27 – June 1, 2004. 28 http://rpitt.eng.ua.edu/Publications/StormwaterTrea tability/Street%20Cleaning%20Pitt%20 29 et%20al%20SLC%202004.pdf 303/15/20 2

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Chapter 3. Controlling Urban Runoff 210 

### 6.9 Constructed Wetlands 1 

### Description of Practice 2 Wetland systems are designed for flood control and removal of pollutants from stormwater. Like 3 natural wetlands, stormwater wetlands (a.k.a. const ructed wetlands) temporarily store the water 4 and have the capacity to improve water quality thro ugh microbial breakdown of pollutants, plant 5 uptake, retention of stormwater, settling and adsor ption (Barr 2001). Constructed wetlands, like 6 wet ponds, incorporate wetland plants into the desi gn and require relatively large contributing 7 drainage areas. As stormwater runoff flows through the wetland, pollutant removal is achieved 8 through settling and biological uptake. Constructed wetlands have zones and plants similar to 9 wet ponds but often with less fluctuation and the a bility to maintain a higher diversity (Shaw 10 2003). 11 Wetlands are among the most effective stormwater pr actices in terms of pollutant removal and 12 also offer aesthetic and habitat value. Although na tural wetlands can sometimes be used to treat 13 stormwater runoff that has been properly pretreated , stormwater wetlands are fundamentally 14 different from natural wetland systems. Constructed wetlands are designed specifically for the 15 purpose of treating stormwater runoff, and typicall y have less biodiversity than natural wetlands 16 in terms of both plant and animal life. Several des ign variations of the constructed wetland exist, 17 each design differing in the relative amounts of sh allow and deep water, and dry storage above 18 the wetland. Sediment forebays and micropools are o ften designed as part of constructed 19 wetlands to prevent sediment from filling the wetla nd. (Barr 2001) 20 A distinction should be made between using a constr ucted wetland for stormwater management 21 and diverting stormwater into a natural wetland. Th e latter practice is not recommended because 22 altering the hydrology of the existing wetland with additional stormwater can degrade the 23 resource and result in plant die-off and the destru ction of wildlife habitat. In all circumstances, 24 natural wetlands should be protected from the adver se effects of development, including impacts 25 from increased stormwater runoff. This is especiall y important because natural wetlands provide 26 stormwater and flood control benefits on a regional scale. (USEPA 2006) 27 

### Photos and Diagrams 28

29 Figure 3-38. Stormwater Wetland 30 Source: USEPA 2006 313/15/20 2

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Chapter 3. Controlling Urban Runoff 211 1 Figure 3-39. Drawing of a wetland 2 Source: Shaw 2003 3

4 Figure 3-40. Plan Diagram of a Shallow Marsh Constr ucted Wetland 5 Source: Barr 2001/Schueller 1992 6

7 Figure 3-41. Stormwater wetland at the University o f Maryland, College Park. 8 Runoff from the parking lot enters the wetland from the left, flows in a roughly U-shaped 9 counterclockwise pattern, and discharges via a rise r a the top center of the wetland. 10 Photo by A.H. Baldwin. (Source: Simpson 2009) 113/15/20 2

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Chapter 3. Controlling Urban Runoff 212 1 Figure 3-42. Photo of Constructed Wetland Basin 2 Source: VA DCR 2009 3

4 Figure 3-43. Plan View Constructed Wetland Basin 5 Source: VA DCR 2009 63/15/20 2

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Chapter 3. Controlling Urban Runoff 213 1 Figure 3-44. Pond/Wetland Combination 2 Source: VA DCR 2009 3

4 Figure 3-45. Plan and Cross Section of Shallow Wetl and 5 Source: VA DCR 2009 63/15/20 2

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Chapter 3. Controlling Urban Runoff 214 

### Common Feasibility Constraints and Limitations 1 Constructed wetlands are widely applicable and can be applied in most regions of the United 2 States, however, there are limitations in specific climates and areas, including : 3

• Arid and semi-arid climates where evaporation makes it difficult to retain water in a 4 shallow pool 5

• ultra urban areas with little pervious surface avai lable for the large land area required 6

• “ hot spots ” that have a high potential for groundwater contami nation, e.g., gas station 7 runoff or areas where chemicals are stored or manag ed 8

• retrofit or new construction in areas with minimal land 9

• cold water trout streams because of thermal effects of heating a shallow pool which can 10 discharge warmer water 11

• breeding ground for mosquitoes in improperly design ed systems 12

• careful selection of plants that will sustain life over the lifetime of the project 13

• nutrient release may occur during the non-growing s eason 14

• consideration of impact on natural wetlands and for ests 15 (Adapted from US EPA 2006) 16 Pollutant Reduction. Considerable variations exist in both methods of r eporting treatment 17 effectiveness, and a broad range of effectiveness i s noted for individual sites. In a literature 18 review conducted for estimating the effectiveness o f these practices in the Chesapeake Bay 19 region, effectiveness estimates for urban construct ed wetlands were 60 percent % for total 20 suspended solids, 20 percent % for total nitrogen and 45 percent % for total phosphorus, and 21 volume reduction was not noted as significant sourc e of pollutant removal. (Simpson 2009). One 22 study found that an experimental system evaluated e xhibited had little potential long-term, 23 consistent for mass removal of total nitrogen and t otal phosphorus, depending on the 24 concentrations in the incoming runoff (Nietch 2005)

. 25 Results from the studies show that some bacteria re moval and inactivation can occur in 26 constructed wetlands. The factors of light, time, a nd temperature, as well as other factors (e.g., 27 predation, sedimentation, sorption, filtration, pH, BOD, pH, and DO) can also contribute to the 28 inactivation of indicator bacteria in constructed w etland BMPs (USEPA 2006). 29 Cold weather performance. Cold winter temperatures may cause freezing of the permanent pool 30 or freezing at inlets and outlets. Also in the wint er, high salt concentrations in runoff from road 31 salting, as well as high sediment loads from road s anding, can impact wetland vegetation. During 32 the spring snowmelt, can carry a relatively high po llutant load with the high volume of runoff. 33 One of the greatest challenges of stormwater wetlan ds, particularly shallow marshes, is that 34 much of the practice is very shallow. Therefore, mu ch of the volume in the wetland can be lost as 35 the surface of the practice freezes. One study foun d that the performance of a wetland system 36 was diminished during the spring snowmelt because t he outlet and surface of the wetland had 37 frozen. Sediment and pollutants in snowmelt and rai nfall events " skated " over the surface of the 38 wetland, depositing at the outlet of the wetland. W hen the ice melted, this sediment was washed 393/15/20 2

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Chapter 3. Controlling Urban Runoff 215 away by storm events (Oberts, 1994). Several design features can help minimize this problem, 1 including : 2

• " On-line " designs allowing flow to move continuously can hel p prevent outlets from 3 freezing 4

• multiple cells, with a berm or weir separating each cell, can help retain storage for 5 treatment above the ice layer during the winter sea son 6

• freeze-resistant outlets (i.e., weirs or pipes with large diameters) 7

• planting salt-tolerant vegetation, such as pickle w eed or cord grass when wetlands drain 8 highway runoff, or parking lots 9

• using a large forebay can help to capture the sedim ent from road sanding. 10 (Adapted from EPA 2006) 11 

### Summaries of Volume and Pollutant Loading Reduction s Achievable 12
Practice Design 13 Several design considerations influence the overall performance of stormwater wetlands, 14 including : 15

• Sufficient drainage area to maintain water in the p ermanent pool, which is typically about 16 25 acres in humid area and more in drier regions 17

• upstream slopes of up to about 15 percent % with shallow local slopes large enough to 18 ensure hydraulic conveyance (generally about three to five foot drop minimum from inlet 19 to outlet) 20

• minor design adjustments for regions of karst (i.e. , limestone) topography to include an 21 impermeable liner 22

• wetlands can intersect the groundwater table, which might affect pollutant reduction 23 capabilities 24

• incorporation of a sediment forebay, a small pool ( typically about 10 percent % of 25 permanent pool volume), to trap coarse particles 26

• surface area of the stormwater wetland should be at least 1 percent % of the drainage area 27

• length-to-width ratio of at least 1.5:1 to prevent “ short circuiting ” 28

• inclusion of both very shallow (<6 inches) and mode rately shallow (<18 inches) to 29 provide a longer flow path through the wetland and encourage plant diversity 30 (Adapted from USEPA 2006) 313/15/20 2

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Chapter 3. Controlling Urban Runoff 216 Design Variations 1 There are three basic design variations of construc ted wetland: 2

• Shallow Marsh: Most of the wetland volume is in the relatively shallow high marsh or 3 low marsh depths with the only deep portions in the forebay at the inlet and the 4 micropool at the outlet. These systems are appropri ate at the terminus of a storm pipe 5 drain or open channel (usually after upland runoff reduction). 6

• Pond/Wetland System: Combining the Wet Pond and sha llow marsh designs requires less 7 surface area than the shallow marsh alone because o f the relatively deep volume of the 8 Wet Pond. These systems are appropriate in moderate ly to highly urbanized areas. 9

• Linear Wetland Cells: Systems installed within the conveyance system or zero-order 10 stream channels. 11 (Adapted from VADCR 2009) 12


### Maintenance Considerations and Resources 13 Typical maintenance activities are as follows ( US EPA 2009): 14

15 Figure 3-46. Constructed wetland maintenance activi ties. 16


### Costs and factors affecting cost 17 The construction cost of urban constructed wetlands varies depending on the design, location, 18 site-specific conditions, etc, being primarily driv en by the most amount of earthwork and 19 planting. (USEPA Wetlands Fact Sheet, 1999). Constr uction cost estimates and references are 20 provided by EPA in the Menu of BMPs Stormwater Wetland Fact Sheet: 21 ( http://cfpub.epa.gov/npdes/stormwater/menuofbmps/in dex.cfm?action=browse&Rbutton=detail 22 &bmp=74&minmeasure=5 ). 233/15/20 2

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Chapter 3. Controlling Urban Runoff 217 The following table provides an example of costs ta ken from North Carolina case studies 1 provided in (Urban Waterways, North Carolina State University Cooperative Extension, 2000, 2 www.neuse.ncsu.edu/SWwetlands.pdf ). 3

4 Figure 3-47. Constructed wetland construction costs

. 5

6 Unit costs for typical wetlands maintenance items a re located in Appendix A of EPA’s 2009 7 Stormwater Wet Pond and Wetland Management Guideboo k 8 ( www.epa.gov/npdes/pubs/pondmgmtguide.pdf ) 9 Example Constructed Wetland Design Manuals in the C hesapeake Bay Watershed Area 10 Virginia Department of Conservation and Recreation Stormwater Design Specification No. 13 11 Constructed Wetlands , Version 1.6, September 30, 2009. 12 www.vwrrc.vt.edu/swc/NonProprietaryBMPs.html 13


### References 14 Barr Engineering Company

. 2001. Minnesota Urban Small Sites BMP Manual, Stormwater Best 15 Management Practices for Cold Climates . Prepared for the Metropolitan Council. 16 www.metrocouncil.org/environment/Water/BMP/CH3_STCo nstWLSwWetland.pdf 17 Hunt, William, B.A. Doll. 2000. et. al. Urban Waterways , Designing Stormwater Wetlands for 18 Small Watersheds , North Carolina State University Cooperative Exten sion, 2000, 19 www.neuse.ncsu.edu/SWwetlands.pdf 203/15/20 2

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Chapter 3. Controlling Urban Runoff 218 Nietch, Chris, et.al. 2005. Nutrient-based ecological consideration for stormwa ter Management 1 basins: Ponds and Wetlands, Paper in the Proceedings of the World Water and 2 Environmental Congress, Anchorage, Alaska, May 15-1 9, 2005. 3 Schueler, T. R., 1992. Metropolitan Washington Coun cil of Governments. Design of Stormwater 4 Wetland System: Guidelines for Creating Diverse and Effective Stormwater Wetlands in 5 the Mid-Atlantic Region. Washington D.C., 1992. 6 Shaw, Daniel and Rusty Schmidt, 2003. Plants for Stormwater Design: Species Selection for the 7 Upper Midwest . Minnesota Pollution Control Agency, Saint Paul, M N, July 2003. 8 Simpson, Tom, Sarah Weammert and Andrew Baldwin

. , 2009. Urban Wet Ponds and Wetlands 9 Best Management Practice

. 10 Struck, Scott, A. Selvakumar, M. Borst. 2006. et.al. Performance of Stormwater Retention Ponds 11 and Constructed Wetlands in Reducing 12 Microbial Concentrations

. USEPA Urban Watershed Management Branch , Water Supply and 13 Water Resources Division , National Risk Management Research Laboratory , EPA/600/R14 06/102 . www.epa.gov/nrmrl/pubs/600r06102/600r06102.pdf , September 2006. 15 U.S. Environmental Protection Agency (USEPA ). ), 2006. NPDES Stormwater Wetland Fact 16 Sheet: Minimum Measure: Post-Construction Stormwate r Management in New 17 Development and Redevelopment , Office of Wastewater Management, Washington, D.C. , 18 May 2006. 19 http://cfpub.epa.gov/npdes/stormwater/menuofbmps/in dex.cfm?action=browse&Rbutton=d 20 etail&bmp=74&minmeasure=5 21 U.S. Environmental Protection Agency (USEPA ). ), 2009. Stormwater Wet Pond and Wetland 22 Management Guidebook , EPA 833-B-09-001. Office of Wastewater Management , 23 Washington, D.C., February 2009. http://www.epa.gov/npdes/pubs/pondmgmtguide.pdf 24 Virginia Department of Conservation and Recreation (VADCR ). ), 2009. Draft VA DCR 25 Stormwater Design Specification No. 13: Constructed Wetlands Version 1.5 , July 2, 2009 26