Created to deliver targeted training on new tools and practices to improve the quality of stormwater runoff.

Transcription

1 BMP Terminology and Design Comparisons Created to deliver targeted training on new tools and practices to improve the quality of stormwater runoff.

2 Outline: 1. Introduction ti 2. Documenting Performance 3. Critical Water Resource Constraints 4. Channel and Flood Protection Design 5. Short Term and Long Term Considerations Chesapeake Bay Stormwater Training Partnership 2

3 A New Generation of Stormwater Management Programs has led to A New Generation of Stormwater Management BMPs Chesapeake Bay Stormwater Training Partnership 3

4 A New Generation of Stormwater Management Programs Stormwater Programs are being updated to: Support S t pollutant t reduction requirements outlined in TMDLs; Waste Load Allocations (WLA) for new and redevelopment may exceed the performance capabilities of current (traditional) Best Management Practices (BMPs); Some TMDLs may address the volume of stormwater runoff as a surrogate pollutant; Chesapeake Bay Stormwater Training Partnership 4

5 A New Generation of Stormwater Management Programs Offer a broader menu of options for achieving compliance; Numerous site design options with associated compliance credits are being recognized by State stormwater programs (MD, VA, WV, DE, etc.) On-site vs off-site compliance options (trading or offset fees) Chesapeake Bay Stormwater Training Partnership 5

6 A New Generation of Stormwater Management Programs Provide a readily implemented method for measuring compliance Site Design Checklists; Concept Design (preliminary) Review; Spreadsheet compliance tools; Chesapeake Bay Stormwater Training Partnership 6

7 A New Generation of Stormwater Management BMPs New SWM programs require a new or updated BMP menu: Achieve superior pollutant t removal performance as demonstrated by sound science and up-to-date research; International Stormwater BMP Database/EPA Urban BMP Performance Tool National Pollutant Removal Database v.3 (CWP 2007); Additional performance credits associated with the volume reduction capabilities of certain BMPs. Chesapeake Bay Stormwater Training Partnership 7

8 A New Generation of Stormwater Management BMPs Consist of a broad selection of structural and non-structural practices; 15 stormwater BMP design specifications 6 new practices Credit for implementing non-structural (environmental site design) practices that preserve or mimic the pre-developed hydrologic response. Chesapeake Bay Stormwater Training Partnership 8

9 A New Generation of Stormwater Management BMPs Easy to understand design and review criteria Detailed comprehensive design specifications; Design review checklists and details; Chesapeake Bay Stormwater Training Partnership 9

10 A New Generation of Stormwater Management BMPs Address construction and long-term maintenance issues through design features Specific requirements for pre-treatment; BMP geometry and flow path criteria intended to enhance performance and longevity; Specific maintenance recommendations. Chesapeake Bay Stormwater Training Partnership 10

11 A New Generation of Stormwater t Management BMPs The new generation of BMPs requires an expanded d approach to BMP Selection and Design: Step 1: Where is your site (state, watershed)? Step 2: What are the critical water resource issues or constraints? ts Step 3: Does the downstream condition require channel or flood protection? Step 4: Are there site-specific physical constraints? Step 5: Are there initial or long-term acceptance considerations? Chesapeake Bay Stormwater Training Partnership 11

12 A New Generation of Stormwater Management BMPs Stormwater BMP Selection: Steps p 1 through 5 may not always follow the same sequence or ranking for BMP selection. However, Step 1 will always be the most important (and maybe easiest) to resolve! Chesapeake Bay Stormwater Training Partnership 12

13 A New Generation of Stormwater Management BMPs Step 1: Where are you? Low Impact Development (LID) Revisited: How low is low? States have established individual metrics for determining the minimum level of implementation. Terminology and Definitions: same term may have different meaning on the other side of the border! Each State is developing or has developed a new or updated stormwater manual. Chesapeake Bay Stormwater Training Partnership 13

14 A New Generation of Stormwater Management BMPs Step 1:Where are you? (what state are you in?) Each State has unique regulatory criteria; Each State has developed compliance criteria and corresponding BMP performance credits; Chesapeake Bay Stormwater Training Partnership 14

15 A New Generation of Stormwater t Management BMPs Terminology: The Maryland Stormwater program utilizes Environmental Site Design (ESD) to replicate pre- development conditions to the Maximum Extent Practicable (MEP); Virginia utilizes the Runoff Reduction Method (RRM) to achieve compliance with a site-based load limit using a selection structural and non- structural management practices; Other Bay watershed States are similarly adopting criteria that require treatment or management of a specified volume of runoff. Chesapeake Bay Stormwater Training Partnership 15

16 Stormwater Management Terminology: We need some new acronyms!! PE ESD ESD v P E ASTM ICP CBSTP IP MEP NRCS Tc P PC PA ESC CA Q RRv ED WQv Tv E Rv Q SA EMC CSN CDA LOD CEC HSG RCA TP Cp v CN SRP TN H:V RCS IC RCN RCN* RSC CPO LDA IDA Chesapeake Bay Stormwater Training Partnership 16

17 Stormwater Management Terminology: A Site Area (acres) MEP Maximum Extent Practicable ASTM A. Society of Testing Materials P Annual Precipitation CA Compost Amendments P E Target Rainfall Depth for Sizing ing ESD Practices (inches) CBSTP Chesapeake Bay Stormwater PA Porous Asphalt Training Partnership CDA Contributing Drainage Area PC Porous Concrete CEC Cation Exchange Capacity Q Runoff Depth (inches) Cpv Channel Protection Volume Q E Target Runoff Depth for Sizing ESD Practices (inches) CSN Stormwater Network Rv Runoff Coefficient CWP Center for Watershed Protection RCN/CN NRCS Runoff Curve Number ED Extended Detention RCN* Composite Curve Number when alternative surfaces are used (IP, PA, PC, Green Roofs, etc.) ESC Erosion and Sediment Control RCA Resource Conservation Area ESD Environmental Site Design RRv Runoff Reduction Volume EMC Event Mean Concentration SA Surface Area of Practice ESC Erosion and Sediment Control SPSC/RSC/ CPO Step Pool Storm Conveyance/Regenerative Storm Conveyance/Coastal Plain Outfalls H:V Horizontal to Vertical (slopes) SRP Secondary RRv Practice HSG Hydrologic Soil Group Tc Time of Concentration IC Impervious Cover TN Total Nitrogen IDA Intensely Developed Area TP Total Phosphorus IP/ICP /C Interlocking Concrete Pavers Tv Water Quality Treatment e t Volume LDA Limited development Area TP Total Phosphorus LOD Limits of Disturbance TN Total Nitrogen WQv Really means Tv Chesapeake Bay Stormwater Training Partnership 17

18 A New Generation of Stormwater t Management BMPs Terminology: Designers should consult the latest stormwater manual or guidance in their respective states. Chesapeake Bay Stormwater Training Partnership 18

19 SWM Program and BMP Design Manual Links: Maryland: 2009 Updates to the 2000 Manual Virginia: Runoff Reduction Practices Pennsylvania: Stormwater BMP Manual 2006 West Virginia: Stormwater Program Delaware: Sediment and Stormwater Program District of Columbia: DDOE SWM Division New York: Stormwater Program Chesapeake Bay Stormwater Training Partnership 19

20 Different Terminology Same Goal Runoff Reduction/Environmental Site Design: The total annual runoff volume reduced through canopy interception, soil infiltration, evaporation, transpiration, rainwater harvesting, engineered infiltration, or extended filtration. Chesapeake Bay Stormwater Training Partnership 20

21 Documenting Runoff Reduction (RR) and Pollutant Removal (PR) Capabilities As expected, stormwater practices vary sharply in their ability to reduce runoff volume Wet Ponds, ED Ponds and Constructed Wetlands and Filters Reduce Runoff Volumes by zero to 10% Bioretention, Infiltration, Dry Swales, Disconnection, and Related Practices Reduce Runoff Volumes by 50 to 90% Chesapeake Bay Stormwater Training Partnership 21

22 Sampling of Compiled Data Sample Runoff Reduction (RR) for Selected BMPs Practice RR (%) Impervious 25 to 50 Disconnection Permeable Pavement 45 to 75 Grass Channel 10 to 20 Bioretention 40 to 80 Infiltration 50 to 90 ED Pond 0 to 15 Constructed Wetland 0 Wet Pond 0 Sample EMC based TP Pollutant Removal (PR) for Selected BMPs Practice TP PR (%) Impervious 0 Disconnection Permeable Pavement 25 Grass Channel 15 Bioretention 25 to 50 Infiltration 25 ED Pond 15 Constructed Wetland 50 to 75 Wet Pond 50 to 75 Range of RR values shown represent median and 75 th percentile RR and PR rates from the research; RR data for some practices were limited, it so some values are considered provisional. Chesapeake Bay Stormwater Training Partnership 22

23 Comparative Runoff Reduction and Nutrient Removal Table BMP design factors that enhance nutrient pollutant removal and runoff reduction were e isolated based on the evaluation ation of the BMP performance literature and research. These factors are incorporated into the BMP design specifications as Level 1 and Level 2 specifications in order to provide increased nutrient reductions. Level 1 achieves the median value of the RR and PR performance values from the research; Level 2 achieves the 75 th percentile value of the RR and PR performance values from the research Virginia utilizes these criteria to achieve the site specific load limits. Maryland is reviewing these specification and performance levels as part of the Critical Areas compliance (but otherwise are not incorporating them into the ESD criteria). Chesapeake Bay Stormwater Training Partnership 23

24 Practice Design Runoff TN EMC TN Load TP EMC TP Load Level Reduction Removal 3 Removal Removal Removal 6 Rooftop Disconnect to to to 50 1 No Level 2 Design Sheet Flow to Veg. Filter 1 25 to to to 50 1 or Conserv. Open Space to to to 75 1 Grass Channels 1 10 to No Level 2 Design Can be used to Decrease Runoff Coefficient for Turf Cover at Site. See the design specs for Soil Compost Rooftop Disconnection, Sheet Flow to Vegetated Filter or Conserved Open Space, and Grass Amendment Channel Vegetated Roof RainwaterHarvesting 1 Up to 90 3, 5 0 Up to 90 3, 5 0 Up to 90 3, 5 No Level 2 Design Permeable Pavement Infiltration Practices Bioretention Practices Urban Bioretention No Level 2 Design Dry Swales Wet Swales Filtering Practices Constructed Wetlands Wet Ponds (20) (20) (45) (45) (30) (30) (65) (65) 4 Ext. Det. Ponds Refer To Next Slide for Footnotes Chesapeake Bay Stormwater Training Partnership 24

25 Notes for Comparative Runoff Reduction and Nutrient Removal Table Notes 1 Lower rate is for HSG soils C and D, Higher rate is for HSG soils A and B. 2 The removal can be increased to 50% for C and D soils by adding soil compost amendments, and may be higher yet if combined with secondary runoff reduction practices. 3 Credit up to 90% is possible if all water from storms of 1-inch or less is used through demand, and the tank is sized such that no overflow occurs. The total credit may not exceed 90%. 4 Lower nutrient removal in parentheses apply to wet ponds in coastal plain terrain. 5 See BMP design specification for an explanation of how additional pollutant removal can be achieved. 6 Total mass load removed is the product of annual runoff reduction rate and change in nutrient EMC. Chesapeake Bay Stormwater Training Partnership 25

26 Level 1 and Level 2 Design Specifications Standard Design Features (included in all designs) needed to maintain proper BMP: Function Safety Appearance Safe conveyance Performance longevity Maintenance Enhanced Design Features include specific design features to improve the BMP s Total Performance (RR, PR, or both). Chesapeake Bay Stormwater Training Partnership 26

27 A New Generation of Stormwater Management BMPs The new generation of BMPs requires an expanded approach to BMP Selection and Design: Step 1: Where are you? Step 2: What are the critical water resource issues or constraints? Step 3: Does the downstream condition i require channel or flood protection? Step 4: Are there site-specific specific physical constraints? Step 5: Are there initial or long-term acceptance considerations? Chesapeake Bay Stormwater Training Partnership 27

28 A New Generation of Stormwater Management BMPs Step 2: What are the critical water resource issues or constraints? Different water resources settings will often limit the selection of BMPs (i.e., performance requirements in certain watersheds); The type of development (highly impervious) paired with certain downstream conditions (cold water fisheries) may further limit the or dictate the BMP options Chesapeake Bay Stormwater Training Partnership 28

29 Application of Stormwater BMPs in Different Water Resource Settings Location and Permit Issues Perennial Streams Wetlands Buffers (RPA, Riparian, etc) 100-year Flood Plain Utilities Roads Chesapeake Bay Stormwater Training Partnership 29

30 Application of Stormwater BMPs in Different Water Resource Settings (continued): Watershed Factors Tributary Strategies Total Maximum Daily Loads Sensitive Waters Water Supply Cold Water Streams Threatened and Endangered Species Chesapeake Bay Stormwater Training Partnership 30

31 Application of Stormwater BMPs in Different Water Resource Settings (continued): Trout Waters: Stormwater transfers heat from pavement and rooftops to receiving streams with runoff temperatures at times exceeding 110 F (CSN Technical Bulletin_); Many aquatic organisms are ectotherms meaning body temperatures are regulated by their surroundings; Trout are especially sensitive to water temperatures, requiring temperatures between 40 and 70 F Higher temperatures also yield lower dissolved oxygen; Some BMPs, especially small volume wet ponds and detention ponds similarly warm during summer months with extremly warm and low DO discharges. Chesapeake Bay Stormwater Training Partnership 31

32 Application of Stormwater BMPs in Different Water Resource Settings (continued): Terrain Factors Physiographic Regions Coastal Piedmont Mountain & Valley Karst Topography Chesapeake Bay Stormwater Training Partnership 32

33 Application of Stormwater BMPs in Different Water Resource Settings (continued): Coastal Plain: Stormwater design in the mid- Atlantic coastal plain is strongly influenced by unique physical constraints and resource sensitivity of the coastal waters. (CSN Technical Bulletin No 2); Flat terrain High water table Highly altered drainage Poorly and very well drained soils Reliance on drinking water wells and septic systems Shoreline buffers and critical areas The highway as a stormwater receiving system Chesapeake Bay Stormwater Training Partnership 33

34 Application of Stormwater BMPs in Different Water Resource Settings (continued): Karst Terrain: A dynamic landscape characterized by sinkholes, springs, caves, and a pinnacled, highly irregular soil-rock interface that is a consequence of the presence of underlying carbonate rocks such as limestone, dolomite and marble (Stormwater Design Guidelines for Karst Terrain in VA). Surface & subsurface drainage patterns are poorly understood. Groundwater contamination risks. Increased Sinkhole Formation Chesapeake Bay Stormwater Training Partnership 34

35 Application of Stormwater BMPs in Different Water Resource Settings (continued): Hotspots: operations or activities that are known to produce higher concentrations of stormwater pollutants and/or have a greater risk for spills, leaks or illicit discharges. The actual hotspot generating area may only occupy a portion of the proposed site. Designers should prepare a Stormwater Pollution Prevention Plan (SWPPP) that outlines pollution prevention and treatment practices that will be implemented to minimize polluted discharges. Depending on severity of the hotspot, there may be restrictions on practices that infiltrate stormwater into groundwater Chesapeake Bay Stormwater Training Partnership 35

36 Application of Stormwater BMPs in Different Water Resource Settings (continued): Comparison of Practices Chesapeake Bay Stormwater Training Partnership 36

37 Practice Karst Coastal Trout Ultra- Terrain 1 Plain 2 Waters 3 Urban 4 Hotspots 5 Rooftop Disconnection Preferred Preferred Preferred Restricted Accepted Sheetflow to Veg. Filter or Cons Open Space Preferred Preferred Preferred Restricted Restricted Grass Channels Accepted Restricted Accepted Restricted Restricted Soil Compost Amendments Accepted Accepted Preferred Preferred Restricted Vegetated Roofs Preferred Accepted Accepted Preferred Accepted Rainwater Harvesting Preferred Preferred Preferred Preferred Accepted Permeable Pavement Preferred Preferred Preferred Preferred Prohibited Infiltration SS: Acc. SS: Acc. LS: Pro. LS: Rest. Preferred Restricted Prohibited Bioretention SS: Acc LS: Rest. Preferred Preferred Preferred Accepted Urban Bioretention Preferred Accepted Restricted Preferred Accepted Dry Swales Preferred Preferred Preferred Restricted Restricted Wet Swales Prohibited Preferred Accepted Restricted Restricted Filtering Practices Preferred Accepted Accepted Preferred Preferred Constructed Wetlands Accepted Preferred Accepted Restricted Restricted Wet Ponds Restricted Accepted Prohibited Restricted Accepted Ext. Detention Ponds Restricted Restricted Restricted Restricted Restricted Refer to next slide for notes. Chesapeake Bay Stormwater Training Partnership 37

38 Comparison of Practices in Different Water Resource Settings KEY Preferred Practice Accepted Practice Restricted Practice Prohibited Practice widely feasible and recommended can work depending on site conditions extremely limited feasibility do not use due to environmental risk NOTES: SS = small scale applications LS = large scale applications 1 CSN Tech Bulletin No. 1 2 CSN Tech Bulletin No. 2 3 CSN Tech Bulletin No. 6 4 CSN Tech Bulletin No. 5 5 CWP Pollution Source Control Practices. Manual 8 in the Urban Subwatershed Restoration Manual Series. Center for Watershed Protection. Ellicott City, MD; CWP (2004) Chesapeake Bay Stormwater Training Partnership 38

39 A New Generation of Stormwater Management BMPs The new generation of BMPs requires an expanded approach to BMP Selection and Design: Step 1: Where are you? Step 2: What are the critical water resource issues or constraints? Step 3: Does the downstream condition i require channel or flood protection? Step 4: Are there site-specific specific physical constraints? Step 5: Are there initial or long-term acceptance considerations? Chesapeake Bay Stormwater Training Partnership 39

40 Integrating Water Quality Treatment with Channel and Flood Control Runoff reduction Credit can be applied to reduce the detention storage volume required for larger design storms 1 (1-yr, 10-yr, etc.); Peak rate of discharge is also influenced by the lengthened Tc associated with non- structural (site design) practices. Effectiveness of RR during larger storms is a function of the relative volume of storage provided versus the volume of runoff. 1 Refer to the Runoff Reduction Method training module for additional information on how the volume credit is applied. Chesapeake Bay Stormwater Training Partnership 40

41 Integrating Water Quality Treatment with Channel and Flood Control Treatment Volume Control of Larger Storm Events Lev1 Lev2 Channel Protection and Peak Discharge Control Capability? Practice ON/ OFF 1 Rooftop Disconnection OFF 1 in * NA Partial, Adjust CDA CN using RRM Spreadsheet Sheetflow to Veg. Filter of OFF 1 in NA Partial, Adjust CDA CN using RRM Spreadsheet Cons Open Space Grass Channels ON 1 in * NA Partial, Adjust CDA CN using RRM Spreadsheet and Increase Tc Soil Compost ON 1 in * NA None Amendments OFF Vegetated Roofs ON 1 in * 1 Partial, Adjust CDA CN using RRM Spreadsheet Rainwater Harvesting ON 1 in * 1.1 Partial, Adjust CDA CN using RRM Spreadsheet Permeable Pavement ON 1 in # 1.1 Partial to Full, Adjust CDA CN using RRM Spreadsheet and Add Storage in Reservoir Partial to Full, Adjust CDA CN using RRM Spreadsheet and Add Infiltration OFF 1 in # 1.1 Storage below underdrain ON Bioretention OFF 1 in # 1.25 Partial to Full, Adjust CDA CN using RRM Spreadsheet and add extra storage on surface, in soil, and below underdrain Urban Bioretention OFF 1in* NA None. Dry Swales ON 1 in * 1.1 Partial, Adjust CDA CN using RRM Spreadsheet and Increase Tc Wet Swales ON 1 in * 1.25 Limited. Adjust Tc Filtering Practices OFF 1 in 1.25 Partial, Adjust CDA CN using RRM Spreadsheet Constructed Wetlands ON 1in Wet Ponds ON 1 in 1.5 Ext. Detention Ponds ON 1 in 1.25 Full. Detention storage can be provided above pool or max ED level in the basin for channel protection and flood control Refer to next slide for notes. Chesapeake Bay Stormwater Training Partnership 41

42 Integrating Water Quality Treatment with Channel and Flood Control Notes: 1 Whether the practice is normally designed as an on-line (ON) or off-line (OFF) relative to the primary flow path (*) () indicates the practice may be designed to provide only a fraction of the treatment volume (Tv) when multiple practices are combined together. (#) indicates that small or micro-scale design applications may be designed with only partial treatment volume. Chesapeake Bay Stormwater Training Partnership 42

43 Integrating Water Quality Treatment with Channel and Flood Control Practice with Runoff Reduction Credit? Yes Practice contains a runoff storage component? Yes RRM Spreadsheet or TR-55 CN Adjustment Detention t or Ext. Detention practice? No No No RRM Spreadsheet CN Adjustment Yes Compute peak discharge with Stage-Storage- Storage Discharge relationships as per guidance Tc Adjustment and compute peak discharge per guidance and/or accepted hydrologic and hydraulic methods Chesapeake Bay Stormwater Training Partnership 43

44 A New Generation of Stormwater Management BMPs The new generation of BMPs requires an expanded approach to BMP Selection and Design: Step 1: Where are you? Step 2: What are the critical water resource issues or constraints? Step 3: Does the downstream condition i require channel or flood protection? Step 4: Are there site-specific specific physical constraints? Step 5: Are there initial or long-term acceptance considerations? Chesapeake Bay Stormwater Training Partnership 44

45 Site Specific Physical Constraints Construction C t ti Erosion and Sediment Control Soil types Depth to water table Depth to bedrock Topography (available head) Available space Chesapeake Bay Stormwater Training Partnership 45

46 Site Specific Physical Constraints: Erosion & Sediment Control Most Runoff Reduction (and Environmental Site Design) practices are not compatible with Erosion and Sediment Control (ESC) measures and should only be installed after final stabilization of the site. Practices that are compatible with ESC (but will still require extensive cleanout of accumulated sediment) include: Grass swales w/ check dams Extended Detention Ponds; Wet Ponds; Constructed Wetlands Chesapeake Bay Stormwater Training Partnership 46

47 Site Specific Physical Constraints: Soil Types Runoff Reduction Practices that utilize infiltration will require a soil test to verify adequate infiltration rate ( 5 in/hr) to a depth below the proposed bottom of the facility. Soils that don t infiltrate (HSG C and D soils) will require an underdrain with a stone sump below the underdrain. Some practices may be utilized in HSG C and D soils with compost amendments, increased residence time, or a secondary practice applied downstream. Chesapeake Bay Stormwater Training Partnership 47

48 Site Specific Physical Constraints: Depth to Water Table or Bedrock Most Runoff Reduction Practices will require a separation of 2 feet from the seasonally high water table or bedrock in order avoid short circuiting of runoff into the groundwater. Some practices, such as wet ponds, wet swales, and constructed wetlands may require groundwater influence in order to maintain a healthy and constant permanent pool volume. Chesapeake Bay Stormwater Training Partnership 48

49 Site Specific Physical Constraints: Topography Steep slopes will always present structural challenges for installing and maintaining stormwater practices. Certain practices can be used, but will require specific controls to ensure adequate retention and residence time (such as check dams in grass swales and dry swales), or multiple cells to ensure minimal ponding depths where required (such as wetlands or bioretention). A minimum drop (hydraulic head: the distance from the ponding surface to the outlet) may be required across some practices in order to ensure that runoff moves through the filter media or drains within the specified time frame. Chesapeake Bay Stormwater Training Partnership 49

50 Site Feasibility Based on Physical Constraints Comparison of Practices Chesapeake Bay Stormwater Training Partnership 50

51 Practice Soils 1 Other Site Constraints 2 HSG A/B HSG C/D DEPTH WT/BR 3 MIN HEAD 4 MAX SLOPE 5 SPACE (%) 6 Rooftop Disconnection B only Yes, w/2 nd RR 7 2ft 1 foot 1-2% Nominal Sheet Flow to Veg. Filter or Conserved Open Space Yes Yes, w/ca 8 2 ft 1-2 ft 6-8% % Grass Channels Yes Yes, w/adrt 10 2ft 2-3 3ft 2-4% 5-15% Soil Compost Amendments Not on A soils Yes 1.5 ft 1 ft 10% Nominal Vegetated Roofs NA 11 NA NA 1-2 ft Varies Nominal Rainwater Harvesting NA NA NA Varies NA Nominal Permeable Pavement Yes, w/ Ad IR 12 Yes, w/ud 13 2 ft 2-4 ft 1-3% 14 Nominal Infiltration Yes w/ Ad IR 12 NO 2 ft 2-4 ft 0 to 5% 1-4% Bioretention Yes Yes, w/ud 13 2 ft 4-5 ft 1 to 5% 3-5% Urban Bioretention NA NA NA 3-5 ft NA Nominal Dry Swales Yes Yes, w/ud 13 2 ft 3-5 ft 4% 5-15% Wet Swales No Yes 0 ft 16 2 ft 2% 5-15% Filtering Practices NA NA 2 ft 2-10 ft NA 0-3% Constructed Wetlands Yes, w/liner 15 Yes Below ft NA 3% Wet Ponds Yes, w/liner 15 Yes Below ft NA 1-3% Ext. Detention Ponds Yes, w/liner 15 Yes 2 ft 6-10 ft NA 1-3% Refer to next slide for notes. Chesapeake Bay Stormwater Training Partnership 51

52 Comparison of Site Feasibility Notes 1 NRCS Hydrologic Soil Groups (HSG) 2 These are general ranges only. 3 vertical distance from bottom invert of practice and water table and bedrock, may be different in karst and/or coastal plain terrain 4 vertical distance from inflow to practice and its bottom invert 5 maximum internal slope of the practice 6 typical footprint of practice as percent of site area 7 with an acceptable secondary runoff reduction practice such as rain garden, dry well or CA-amended filter path 8 filter strip w/ compost amendment (CA) 9 6% for conservation filter and 8% for grass filter strip 10 grass swale must achieve adequate (Ad) residence time (RT) 10 min 11 Not Applicable (NA) 12 with adequate (Ad) measured infiltration rate (IR) of 0.5 inches/hr 13 with underdrain 14 slopes can be broken up by terracing. 15 depending on borings, a liner may be needed to hold water 16 for water table only, 2 foot distance to bedrock still required Chesapeake Bay Stormwater Training Partnership 52

53 Site Specific Physical Constraints: Available Space Most Runoff Reduction Practices are especially well suited for small or Ultra Urban development sites (i.e.: micro-scale Bioretention). However, high density residential and commercial settings where space is limited will still require adequate space for Standard Design Features such as pre-treatment, maintenance access, geometry, etc. Public acceptance of stormwater practices can be negatively influenced by inadequate spacing or buffer. Safety and aesthetic issues are magnified in high traffic areas. Chesapeake Bay Stormwater Training Partnership 53

54 Spatial Scale at Which Practices Are Applied Most Runoff Reduction (and Environmental Site Design) practices are applied at a smaller spatial scale than previous stormwater practices; meaning more practices on any given site: Micro Scale Small Scale Normal Scale Moderate Scale Large Scale Chesapeake Bay Stormwater Training Partnership 54

55 Practice Micro Scale Small Scale Normal Scale ModerateScale LargeScale Rooftop Disconnection Sheet Flow to Veg. Filter or Conserved Open Space Grass Channels Soil Compost Amendments Vegetated Roofs Rainwater Harvesting Permeable Pavement Infiltration Bioretention Urban Bioretention Dry Swales Wet Swales Filtering Practices Constructed Wetlands Wet Ponds Ext. Detention Ponds 250 to 1,000 sf 250 sf to 2 acres Residential 250 to 2,000 sf 1,000 to 5,000 sf 250 to 1,000 sf 1,000 to 10,000 sf 250 to2,500 sf 2,500 to 20,000 sf 250 to2,500 sf 2,500 to 20,000 sf 250 to2,500 sf 2,500 to 20,000 sf 5,000 to 25,000 sf 20,000 sf to 250,000 sf Commercial 2,000 to 200,000 sf 10,000 to 200,000 20,000 to 100,000 sf 20,000 to 100,000 sf 20, to 250, sf 20,000 to 250,000 sf 20,000 to 250,000 sf 10 + more acres, unless favorable water balance Chesapeake Bay Stormwater Training Partnership 55

56 A New Generation of Stormwater Management BMPs The new generation of BMPs requires an expanded approach to BMP Selection and Design: Step 1: Where are you? Step 2: What are the critical water resource issues or constraints? Step 3: Does the downstream condition i require channel or flood protection? Step 4: Are there site-specific specific physical constraints? Step 5: Are there initial or long-term acceptance considerations? Chesapeake Bay Stormwater Training Partnership 56

57 Initial and Long Term Considerations: Initial Cost (highly variable based on location and other factors) Land opportunity costs Construction costs Initial Practice Construction costs vs Site-Scale Life Cycle costs Long Term Costs Operation and Maintenance Community Acceptance Aesthetics ti Potential Nuisance Conditions Safety Wildlife Habitat Other Chesapeake Bay Stormwater Training Partnership 57

58 Initial and Long Term Considerations: Initial Costs Construction ti (specialized equipment, materials, or expertise) can be highly variable based on location and other factors; Land opportunity costs: Runoff Reduction practices that may be expensive to construct but ultimately save buildable space on the site represent a potential long term cost benefit. Long Term Costs Operation and Maintenance of practice Total life cycle costs: a green roof may save on long term building heating and cooling costs; roofing materials life expectancy ; and additional benefits from LEED or other Green building certifications Community Acceptance - How will the practice be accepted by the neighboring community: Aesthetics Potential Nuisance Conditions Safety Wildlife Habitat t Other Chesapeake Bay Stormwater Training Partnership 58

59 Maintenance and Inspections Maintenance is essential to ensure that all SWM BMPs remain in proper working order and achieve their hydrologic and pollutant removal performance goals over time; The frequency of maintenance is very site specific (How much did it rain?; How dirty is the site?) Individual id site inspections are essential to evaluating the maintenance requirements. BMP design specifications include detailed information on how to conduct maintenance inspections; and Indicators for performing specific maintenance tasks that must be done to ensure continued performance and longevity. The following is an example from Permeable Pavements: Chesapeake Bay Stormwater Training Partnership 59

60 Suggested Annual Maintenance Inspection Points for Permeable Pavement Activity The drawdown rate should be measured at the observation well for three days following a storm event in excess of 0.5 inch in depth. If standing water is still observed in the well after three days, this is a clear sign that that clogging is a problem. Inspect the surface of the permeable pavement for evidence of sediment deposition, organic debris, staining or ponding that may indicate surface clogging. If any signs of clogging are noted, schedule a vacuum sweeper (no brooms or water spray) to remove deposited d material. Then, test t sections by pouring water from a five gallon bucket to ensure they work. Inspect the structural integrity of the pavement surface, looking for signs of surface deterioration, such as slumping, cracking, spalling or broken pavers. Replace or repair affected areas, as necessary. Check inlets, pretreatment cells and any flow diversion structures for sediment buildup and structural damage. Note if any sediment needs to be removed Inspect the condition of the observation well and make sure it is still capped Generally inspect any contributing drainage area for any controllable sources of sediment or erosion Chesapeake Bay Stormwater Training Partnership 60

61 BMP Selection and Location Criteria Best Professional Judgment: Site Criteria Stormwater Treatment Objectives and Performance Goals Pollutant Load Reduction Nutrient Reduction Runoff Reduction Sediment Reduction Hot Spots Channel Protection Flood Control Long Term Operation and Maintenance Chesapeake Bay Stormwater Training Partnership 61

62 Refer to Individual BMP Training Modules for Specific BMP Selection and Design Guidance. Chesapeake Bay Stormwater Training Partnership 62