Basics of ESD and the New Design Sequence

Transcription

1 Basics of ESD and the New Design Sequence

2 Visit: To learn how you can have access to: Discounted Webcasts Free One-day design workshops Intensive master stormwater design seminars Direct On-site technical assistance Self guided web-based learning modules

3 Agenda 1. Why ESD is Important to the Bay 2. The New Design Sequence and Spreadsheet 3. Using Alternative Surfaces and Credits 4. Design of Micro- ESD Practices

4 The Bay Stormwater Problem Stream habitat and biodiversity degraded in 10,000 stream miles in the Bay watershed Major ecological impacts in small estuaries and coastal creeks Fastest growing nutrient load source in the Bay watershed Pesticides detected in 95% of urban streams and fish tissues sampled Metals, PCBs and hydrocarbons in tidal sediments Bacteria violations in runoff close streams, beaches and shellfish beds Our traditional stormwater practices have not solved these problems

5 Our Traditional Stormwater BMPs Have Not Worked Excellent Piney Branch - WBPB203A Percent of Best Possible BIBI Score Good Fair Poor 10 0 Avg Pre-development IBI Avg Post-development IBI Avg During-construction IBI

6 The New Maryland ESD Regulations You are not alone..tougher stormwater regulations are on the horizon in all Bay states:

7 Maximum Extent Practicable is defined as maintaining predevelopment site runoff to woods in good condition. The resulting ESD volume typically ranges between 1.7 and 2.6 inches, depending on soils and development intensity

8 Features of the CSN ESD to MEP Compliance Spreadsheet Automatically Calculates ESD Target Volume Accounts for all of the credits, alternative surfaces, micro-esd practices and conventional practices in a step-wise fashion Simultaneously tracks ESD volume and Critical Area 10% requirements Easy to verify compliance

9 Status of Compliance Spreadsheet Spreadsheet and Users Guide are available at Has undergone significant testing Version 2.0 was released in June, 2010 Version 2.1 released in July 2010

10 Before You Get Started Site Recon (understand the site) Environmental mapping (protected areas) Define small drainage areas and flow paths ID locations of most permeable soils Develop site plan that shows impervious and pervious cover footprints

11 Site mapping and stormwater concept plans are mandated at the earliest stages of development plan review Natural Resource Inventory and Mapping Better Site Design to Minimize Impervious Area Disconnection and Filter Strips Integrate ESD Practices into the Best Soils Using Natural Flow Pathways for Stable Conveyance

12 Site mapping and stormwater concept plans are mandated at the earliest stages of development plan review

13 Mapping Requirements Wetlands Major Water Ways Floodplains Critical Areas Wetland Buffers Perennial Streams Stream Buffers Forest Stand Delineation Steep slopes Springs and seeps Highly erodible soils Topography Existing drainage area Hydrologic Soil Groups Zero-order streams

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15 Start By Reducing Clearing and Preserving Highly Permeable Soils

16 Step 1 ESD Site Planning Checklist Must answer 12 questions related to ESD site and stormwater planning Should be able to answer Yes or does not apply Show on the site plan If answer is No, must provide a written narrative. as to why it could not have been used

17 The basic idea is that a compliant plan is one without any no s (either a yes or not applicable) ESD Implementation Checklist Check all of the Following ESD Practice That Were Implemented at Site Yes No N/A Environmental Mapping Was Conducted at Site Prior to Layout Natural Areas Were Conserved (e.g., forests, wetlands, steep slopes, floodplains) Stream, Wetland and Shoreline Buffers Were Reserved Disturbance of Permeable Soils Was Minimized Natural Flow Paths Were Maintained Across the Site Building Layout Was Fingerprinted to Reduce Clearing and Grading at Site Site Grading Promoted Sheetflow From Impervious Areas to Pervious Ones Site Design Was Evaluated to Reduce Creation of Needless Impervious Cover Site Design Was Evaluated to Maximize Disconnection of Impervious Cover Site Design Was Evaluated to Identify Potential Hotspot Generating Area for Stormwater Treatment Erosion and Sediment Control Practices and Post Construction Stormwater Management Practices Were Integrated into a Comprehensive Plan Tree Planting Was Used at the Site to Convert Turf Areas into Forest X X X X X X X X X X X X

18 Step 2 Calculate Site IC and WQv Four Basic Inputs: Site Area Existing Site Impervious Cover Area Proposed Site Impervious Cover Area WQv Rainfall Depth (0.9 or 1.0) Impervious cover is measured as any area without vegetative or pervious cover Step 2: Calculate Site Imperviousness and Water Quality Volume, WQv Site Area, A (acres) 38 Existing Impervious Surface Area (acres) 0 Proposed Impervious Surface Area (acres) Existing Imperviousness, I pre 0.0% Proposed Imperviousness, I post 36.3% Development Category New Development Rainfall Depth, P (in) 1.0 Runoff Coefficient, Rv 0.38 Water Quality Volume, WQv (ac-in) Water Quality Volume, WQv (cf) 51,982

19 CSN Tip: Break sites up into 2 to 5 acre sub-drainage areas, define natural flow paths, and make best estimate of IC (and increase it by 15%)

20 Step 3 Compute MD Critical Area Phosphorus Removal Requirement * Automatically calculates the phosphorus removal requirement, depending on whether the site is classified as new development or redevelopment (>15% IC). * This requirement applies to Intensely Developed Areas in the 1000 ft Critical Area

21 Step 4 Enter Pre-development Soil Data Enter Percent Site Area in Hydrologic Soil Group A, B, C or D Automatically computes ESD rainfall Target Volume, and the Recharge Volume Your HSGs will determine your ESD strategy.

22 Output From Spreadsheet in this Step % Soil Type A 0% % Soil Type B 60% % Soil Type C 40% % Soil Type D 0% Pre-Developed Condition, RCN woods 61 New Development Soil Type A ESD Rainfall Target, P E (in) 0.00 Soil Type B ESD Rainfall Target, P E (in) 1.08 Soil Type C ESD Rainfall Target, P E (in) 0.72 Soil Type D ESD Rainfall Target, P E (in) 0.00 Site ESD Rainfall Target, P E (in) 1.80 ESD Runoff Depth, Q E (in) 0.68 ESD Runoff Volume, ESDv (cf) 93,567 Required Recharge Volume, Re v (ac-ft) 0.25 Required Recharge Volume, Re v (cf) 10,812

23 Step 5 Select Alternative Surfaces Look at areas at Site where Green Roof or Permeable Pavers Can be Used Enter area and thickness The spreadsheet then reduces the ESD Rainfall Target volume and adjusts the Phosphorus removal rate accordingly Alternative Surfaces Drainage Area (ac) Thickness Effective RCN Green Roof (on Soil Type A) 0. Green Roof (on Soil Type B) 0 Green Roof (on Soil Type C) 0 Green Roof (on Soil Type D) 0 Permeable Pavement (Soil Type A) 0 Permeable Pavement (Soil Type B) 0 Permeable Pavement (Soil Type C) 0

24 Permeable Pavements

25 Alternative Surfaces: Green Roof CSN Tip: Design spec available on CSN website

26 Step 6 Utilize Disconnection and Filtering Credits Three broad credits Rooftop Disconnection Non-rooftop Disconnection Expanded Conservation Area Enter the CIDA (contributing impervious drainage area) and a few simple design parameters. Must also enter the predominant pre-development HSG of the filter path to compute the TP reduction

27 CSN Tip: Connect CIDA blobs with pervious blobs on plan and check distances/slopes. OK to aggregate acceptable credits in the spreadsheet Step 6: Select Nonstructural Practices to Treat the ESD Rainfall Target Nonstructural Practices P E Credit Description Contributing Impervious Cover (ac) Direct ESDv Received by Practice (cf) ESDv from Upstream Practices (cf) Practice Specific Parameter(s) P E Credit (in) ESDv credit (cf) Runoff Volume Remaini ng (cf) Enhance d Filter Volume (cf) Rev (cf) Disconnection of Rooftop Runoff (A/B Soils) Disconnection of Rooftop Runoff (C/D Soils) Up to 1 inch credit provided based upon disconnection flow length. 3 18,622 0 Flow Path (ft) 75 East/West Western Shore 1 10,346 8,276 10,346 Up to 1 inch credit provided based upon disconnection flow length Disconnection of Non-Rooftop Runoff (A/B Soils) Disconnection of Non-Rooftop Runoff (C/D Soils) Sheetflow to Conservation Areas (A/B Soils) Up to 1 inch credit provided based upon disconnection and contributing flow lengths. 0 0 Disconnection Length (ft) Contributing Length (ft) (Impervious) Up to 1 inch credit provided based upon disconnection and contributing flow lengths Up to 1 inch credit provided based upon conservation area width Minimum Width (ft) ,465-7,465 7,465

28 Credits Are Easy to Show on Plan But Will They Actually Show Up at the Site? Four Stage Review: 1. Evaluate Feasibility During Concept Design 2. Confirm Area in Final Design 3. Protect During Construction inspection 4. Verify as Part of Final Stormwater Acceptance

29 Step 7 Apply ESD Micro-Practices 100% IA to micro-practices Enter CIDA, and specific design parameters for each micro-practice selected Can select a downstream practice to which runoff will flow to HSG are. used to make sure that the Micropractices are properly applied to the right soil, and adjust TP removal rate

30 Micro-ESD Practices Rainwater Harvesting Submerged Gravel Wetland Micro-Infiltration (Dry Well) Micro-bioretention * Rain farden Landscape Infiltration Grass Swales Bioswales* Wet Swales Enhanced Filters are add on to * practices

31 It seems complex, but only a few inputs are needed Step 7: Select Micro-Scale Practices to Treat the ESD Rainfall Target Micro-Scale Practices Rainwater Harvesting Submerged Gravel Wetlands Micro- Infiltration Rain Gardens (A/B Soils) Rain Gardens (C/D Soils) Bioretention (A/B Soils) Bioretention (C/D Soils) Landscape Infiltration Grass Swales (A/B Soils) Grass Swales (C/D Soils) Bio-swales (A/B Soils) Bio-swales (C/D Soils) Wet Swales P E Credit Description CDIA (ac) Direct ESDv ESDv Received from Up by Practice Practice (cf) s (cf) P E credit is based on design volume 0 0 P E credit is based on design volume 0 0 P E credit is based on design volume 5 31,037 0 P E = 10" x Surface Area / Drainage Area 0 0 Practice Specific Parameter(s) Design Volume (cf) Surface Area (sf) Depth* (ft) 2.2 Surface Area (sf) 11, Surface Area (sf) Depth* (ft) P E ESDv credit (cf) Enhance d Filter Volume (cf) Rev (cf) ,600 13,437 17, P E = 10" x Surface Area / Drainage Area Surface Area P E = 15" x Surface Area / (sf) Drainage Area 5 31, , ,750 7,287 23,750 P E = 15" x Surface Area / Drainage Area Surface Area P E = 20" x Surface Area / (sf) Drainage Area Surface Area P E = 10" x Surface Area / (sf) Drainage Area 0.8 4, , ,325 1,641 3,325 P E = 10" x Surface Area / Drainage Area Surface Area P E = 15" x Surface Area / (sf) Drainage Area P E = 15" x Surface Area / Drainage Area Surface Area P E credit is based on design volume 0 0 (sf) Depth* (ft) Downstream Practice Sheetflow to Conservation Areas (A/B Soils) Grass Swales (A/B Soils)

32 Step 8 Check for ESD Compliance and Go Back Minimum ESD For Full WQv Entire Rev Zero TP removal requirement Must Attempt to Provide ESD for Full ESD Target Volume.

33 Several iterations are needed to get to compliance ESDv Treated (cf) 62,485 Total Re v (cf) 62,485 P E achieved (inches) 1.20 WQv Requirements Met Through Environmental Site Design? YES WQv Remaining? (cf) 0 Entire ESDv Treated Through Environmental Site Design? NO ESDv Remaining? (cf) 31,082 Re v Requirements Met Through Environmental Site Design? YES Re v Remaining? (cf) 0

34 Strategies to Achieve Compliance Adjust site layout to reduce IC or increase forest cover. Make sure that all the No s are addressed Consider more alternative surfaces (most designers will have skipped this step initially) Expand site area subject to credits (e.g., more disconnection, improve soil and slope conditions within filter strip, accept concentrated flows w/ level spreader)

35 Strategies to Achieve Compliance (continued) Add more Micro-ESD practices to pick up addl. untreated CIDA Change ESD practices to get higher runoff reduction (e.g., go from grass channel to bio swale, or from rain garden to micro-bioretention Add an Enhanced Filter to the bottom of select micro-esd Practices

36 Strategies to Achieve Compliance (continued) UPGRADE: Substitute Larger ESD practices such as Bioretention, Dry Swales and Infiltration that pick up more CIDA or have higher runoff reduction Do more soil infiltration testing to find best sites ESD basins Use bioretention within ED or flood control pond (at smaller sites) Subarea Over-control As long as they drain to same area, OK to over control in one DA to compensate for under-control in another

37 Step 9 Compute reduced RCN for CPv Calculations Automatically calculates a new runoff curve number (RCN) to calculate the remaining storage volume needed for channel protection that reflects the final combo of ESD practices employed. The RCN can also be used in hydrologic models for peak discharge calculation. Reduced RCN for Type A Soils 42 Reduced RCN for Type B Soils 63 Reduced RCN for Type C Soils 77 Reduced RCN for Type D Soils 81 Composite Reduced RCN 69 Q (in) 0.45 CPv Treatment Required (cf) 62,511

38 Step 10 Apply Structural Practices for remaining Compliance Only after you have exhausted your ESD opportunities Conventional practices can be used to obtain any remaining Rev, Cpv, WQv or TP removal for site compliance Simplified List: Ponds, Wetlands, Filters These practices. are independently sized and designed

39 Note Level 1 and 2 Design for Critical Area Contributing Direct ESDv ESDv from Enhanced Filter Phosphor ous Load Reducti Impervious Received by Upstream Treatment Volume Removal on Structural Practices Cover (ac) Practice (cf) Practices (cf) Volume (cf) (cf) Rev (cf) Efficiency (lbs/yr) Stormwater Ponds (Level 1) % 0.00 Stormwater Ponds (Level 2) % 0.00 Stormwater Wetlands (Level 1) % 0.00 Stormwater Wetlands (Level 2) % 0.00 Stormwater Filtering Systems (Level 1) % 0.00 Stormwater Filtering Systems (Level 2) % 0.00 Stormwater Infiltration (Level 1) % 0.00 Stormwater Infiltration (Level 2) % 0.00 Total structural CPv provided 0 Total Load Reduction (lbs P / year) CPv Requirement Met? NO Total Load Reduction Remaining (lbs P / yr) 0.00 CPv Remaining 62,511 Total Re v provided (cf) 62,485 Re v Requirement Met? YES Re v Remaining? (cf) 0

40 Step 11 Additional Concept Design Work Site plan showing CIDA and surface area of individual ESD practices Site testing to confirm feasibility of ESD practices (e.g., water table, slopes, sheet flow distances, infiltration rates, etc). Analyze system of ESD practices for safe conveyance. of the 10 year storm ESC plan that shows how ESD practices will be protected during construction

41 CONSTRUCTION CONSTRAINTS FOR ESD MICRO-PRACTICES ESD PRACTICE Install After Con. Avoid or Protect Do not use as ESC Restore Soil Disconnect/Filter credits X X X X Permeable Paver X X X X Rainwater Harvesting X Gravel Wetlands X X X X Micro-infiltration X X X X Rain Garden X X X X Bioretention X X Landscape Infiltration X X X X Grass Swales X X Bioswales X X Wet Swales X X Enhanced Filters X X X X

42 Solution: Rain gardens or rainwater harvesting

43 Step 12 Final design and installation This is where the rubber meets the road!.

44 Alternative Surfaces and Credits

45 Alternative Surfaces Alternative Surfaces Permeable Pavers Green Roofs How they work Dealing with design and installation issues

46 Select Alternative Surfaces Look at areas at Site where Green Roof or Permeable Pavers Can be Used Enter area and thickness The spreadsheet then reduces the ESD Rainfall Target volume accordingly Alternative Surfaces Drainage Area (ac) Thickness Effective RCN Green Roof (on Soil Type A) 0. Green Roof (on Soil Type B) 0 Green Roof (on Soil Type C) 0 Green Roof (on Soil Type D) 0 Permeable Pavement (Soil Type A) 0 Permeable Pavement (Soil Type B) 0 Permeable Pavement (Soil Type C) 0

47 Alternative Surfaces: Permeable Pavements

48 Design Scales for Permeable Pavers Micro-Scale Small-Scale Large-Scale Design Factor Suitable Paver PICP ALL ALL Reservoir Size Some or all of the RRv or WQv Full WQv, and as much of CPv and design storms as possible External DA? No Yes, Impervious cover up to twice the permeable paver area may be accepted Observation Well No No Yes Underdrain? Rare Depending on soils Back up underdrain

49 Comparative Properties of the Three Major Permeable Paver Design Factor Porous Concrete (PC) Porous Asphalt (PA) Interlocking Pavers (PICP) Scale of Application Small and Large Scale Applications Small and Large Scale Applications Micro, Small and Large Scale Applications Paver Thickness Design Permeability Construction Cost Min Batch Size 5 to 8 inches 3 to 4 inches 3 1/8 inches 10 feet/day 6 feet/day 2 feet/day $ 2.00 to $6.50 sf $ 0.50 to $1.00/sf $ 5.00 to $ 10.00/sf ~ 500 sf NA Longevity 20 to 30 years 15 to 20 years 20 to 30 years Colors & Texture Limited Range of Colors and Textures Black or Dark Grey Color Range of Colors and Textures

50 Permeable Paver ESD Sizing and Applicability Effective RCNs for Permeable Pavements Hydrologic Soil Group Subbase A B C D Design shall include overdrain (inv. 2 below pavement base) If sub-base is greater than 12 or under drains are used on D soils, then skip this step, and enter as an upgraded BMP later on

51 MDE Guidance on Permeable Pavers Not allowed on D soils or Fill Soils Porosity = 30% More than 10,000 sf = must have tested infiltration rate of more than 0.52 in/hr Under-drain OK for smaller projects CSN Tip: Detailed paver design spec available at

52 Paver Design Modification Enhanced Filter Source: Hunt and Collins, 2008

53 Enhanced Filters The stone reservoir volume is equal to the surface area multiplied by depth divided by the porosity (n) of the stone Used to address Rev for the contributing impervious area using the percent volume method. When coupled with other properly designed structural or micro-scale practices, the combined system will address the ESD sizing criteria.

54 Reinforced Turf Post development RCN s for reinforced turf applications should reflect the surfacing material used (e.g., open space in good condition for grass).

55 Green Roof Sizing Only used to reduce curve number No direct reduction of ESD volume Rev must be provided separately Effective RCNs for Extensive Green Roofs Roof Thickness (in.): Effective RCN:

56 Disconnection and Filtering Credits Three broad credits Rooftop Disconnection Non-rooftop Disconnection Expanded Conservation Area Enter the CIDA (contributing impervious drainage area) and a few simple design parameters. Must also enter the predominant pre-development HSG of the filter path to compute the TP reduction

57 CSN Tip: Connect CIDA blobs with pervious blobs on plan and check distances/slopes. OK to aggregate acceptable credits in the spreadsheet Step 6: Select Nonstructural Practices to Treat the ESD Rainfall Target Nonstructural Practices P E Credit Description Contributing Impervious Cover (ac) Direct ESDv Received by Practice (cf) ESDv from Upstream Practices (cf) Practice Specific Parameter(s) P E Credit (in) ESDv credit (cf) Runoff Volume Remaini ng (cf) Enhance d Filter Volume (cf) Rev (cf) Disconnection of Rooftop Runoff (A/B Soils) Disconnection of Rooftop Runoff (C/D Soils) Up to 1 inch credit provided based upon disconnection flow length. 3 18,622 0 Flow Path (ft) 75 East/West Western Shore 1 10,346 8,276 10,346 Up to 1 inch credit provided based upon disconnection flow length Disconnection of Non-Rooftop Runoff (A/B Soils) Disconnection of Non-Rooftop Runoff (C/D Soils) Sheetflow to Conservation Areas (A/B Soils) Up to 1 inch credit provided based upon disconnection and contributing flow lengths. 0 0 Disconnection Length (ft) Contributing Length (ft) (Impervious) Up to 1 inch credit provided based upon disconnection and contributing flow lengths Up to 1 inch credit provided based upon conservation area width Minimum Width (ft) ,465-7,465 7,465

58 Lots of opportunity to boost the hydrologic function of urban turf through ESD Credits

59 Our Turf Is Not Very Pervious and is Ineffective in Treating Stormwater Top Soil is Stripped Soil Structure is Lost Subsoils are Compacted Reduced Water Holding Capacity Low Infiltration Rate High Nutrient Concentrations Runon to Impervious Cover

60 Soil Restoration is Not Recommended When: Existing soils have high infiltration rates (e.g., HSG A soils) The water table or bedrock is located within 1.5 feet of the soil surface. Slopes exceed 10%. Existing soils are saturated or seasonally wet They would harm roots of existing trees (stay outside the tree drip line) The downhill slope runs toward an existing or proposed building foundation The contributing impervious surface area exceeds the surface area of the amended soils

61 MDE Simple Disconnection Min. 15 feet length 10 feet lateral setback to IC Max Filter Path 0f 75 ft Max of 500 sf of IC per disconnect (1000 for nonrooftop) Max 5% slope w/o infiltration berms A, B and C soils OK, soil amendments may be needed on D soils or disturbed soils Flows shall be non-erosive for two year storm

62 Rooftop Disconnection MDE Sizing and Applicability Applies to all development types of low to moderate intensity ESD Sizing Factors for Rooftop Disconnection Disconnection Flow Path Length (ft.) Western Shore Eastern Shore PE (in.) =

63 Disconnect to Grass Filter Strip ESD Sizing Non-Rooftop Disconnection Ratio of Disconnection Length to Contributing Length Impervious Ratio 0.2:1 0.4:1 0.6:1 0.8:1 1:1 PE (in.) =

64 CSN Design Guidelines for Grass Filter Strip Soil and Ground Cover Construction Stage Typical Application Compost Amendments Boundary Spreader Boundary Zone Concentrated Flow? Entrance Slope Maximum Overall Slope Amended Soils and Dense Turf Cover Prevent Soil Compaction by Heavy Equipment Treat Small Areas of Impervious Cover Close To Source (max of 5000 square feet) Yes Gravel Diaphragm at Top of Filter Permeable Berm at toe of filter At 25 feet of level grass Not Recommended Less than 2% in first ten feet of strip 5%

65 Sheet flow to Conservation Area (CA)

66 MDE Conservation Area Rules Max Slope of 5% in CA Max IC length of 75 ft to CA CA must be at least 20,000 square feet in area CA must have min. width of 50 ft No managed turf in CA Sheetflow to Conservation Area Sizing Factors Min. Width (ft) = PE (in.) =

67 CSN Supplemental Guidelines for Conservation Filters Soil and Ground Cover Construction Stage Typical Application Compost Amendments Boundary Spreader Boundary Zone Concentrated Flow? Max Entrance Slope Site Reconnaissance Undisturbed Soils and Native Vegetation Located Outside the Limits of Disturbance and Protected by ESC Perimeter Controls Adjacent Drainage to Stream Buffer or Forest Conservation Area No Infiltration Berm at Top of Filter 10 feet of Level Grass Runoff should enter the boundary as sheetflow for the one-inch storm or use concrete engineered level spreader Less than 4% in the first ten feet of filter Site visit to confirm topography, slope, and soil conditions prior to design

68 Infiltration Berm

69 Critical Area Buffer General rule is to keep stormwater treatment out of the 100 foot buffer OK to use bioretention and filter strip at boundary Exceptions: Use of regenerative conveyance wetlands through the buffer in zero-order streams or ditches Use bioretention or other practices with trees in buffer exception areas?

70 CSN Tip: Provide a Credit for Soil Restoration and Examples of Qualifying Criteria Reforestation Minimum area of 5000 sf Stormwater or conservation easement Long term forest plan Achieve 75% forest canopy in 10 years Show on all ESC drawings

71 Credits Are Easy to Show on Plan But Will They Actually Show Up at the Site? Four Stage Review: 1. Evaluate Feasibility During Concept Design 2. Confirm Area in Final Design 3. Protect During Construction inspection 4. Verify as Part of Final Stormwater Acceptance

72 Design of ESD Micro-Practices

73 The List of Micro-ESD Practices Rainwater Harvesting Submerged Gravel Wetland Micro-Infiltration (Infiltration) Rain Garden * Micro-bioretention (Bioretention) * Landscape Infiltration Grass Swales Bioswales) (Dry Swales) * Wet Swales Enhanced Filters are add on to * practices Micro practices should be used to achieve entire ESD volume, or at least the entire water quality volume

74 Your HSG s Determine Which Micro-Practices Are Feasible ESD PRACTICE HSG A HSG B HSG C HSG D Permeable Paver X X X Rainwater Harvesting X X X X Submerged Gravel X X Wetlands Micro-infiltration X X Rain Garden X X X Bioretention X X X Landscape Infiltration X X Grass Swales X X X Bioswales X X X X Wet Swales X X Enhanced Filters X X X= may be suitable depending on depth to water table, bedrock and slope

75 Comparing the Micro-Practices ESD PRACTICE ESD Efficiency Max CDA (sf) Upgrade Size? Rainwater Harvesting 20+ ~20,000 Yes Gravel Wetlands ~10 < 1 acre No Micro-infiltration Yes Rain Garden 10 2,000 No Micro-Bioretention 15 20,000 Yes Landscape Infiltration 20 20,000 No Grass Swales 10 > 1 acre No Bioswales 10 > 1 acre Yes Wet Swales 15 > 1 acre? Enhanced Filters ~6 n/a No

76 Landscape Infiltration Four layer System Surface ponding 12 inch of planting soil 12 inch of gravel 12 inch of sand.

77 Landscape Infiltration Restricted to A & B soils Max CDA of 10,000 sf (w/o soil testing and pretreatment) This has the best ESD reduction of any micro-esd practice per square foot of practice surface area. Essentially an infiltrating bioretention facility w/o underdrain

78 Submerged Gravel Wetland

79 Submerged Gravel Wetland C or D Soils High Water Tables and Eastern Shore Minimum CDA of 1 acre 18 to 48 inches of gravel Pretreatment required Updated design guidance available from UNH as Resource 5

80 Submerged Gravel Wetland Sizing PE for the contributing drainage area is based on the volume captured by submerged gravel wetlands. Assume about 10 inches

81 Dry Well = Micro-infiltration

82 Dry-Well (Micro-Infiltration) ESD Sizing A PE value based on the ESDv captured and treated shall be applied to the contributing drainage area. The storage area for the ESDv includes the sand and gravel layers in the bottom of the facility. Assume about 15 inches

83 Dry Well = Micro-infiltration A and B Soils Max CDA of 500 sf Above this shift to normal infiltration trench design Pretreatment Bottom sand layer 10 feet setback from foundations

84 Process for Investigating Infiltration Feasibility at a Site Preliminary Look at Soil Survey but don t put too much stock in it Geophysics for Site would also be good for general site layout issues (e.g., best places for infiltration, best places for wells) On-Site Soil Test at Actual Facility Location: Bore Hole or Test Pit Drawdown Test (see Infiltration Spec Appendix) Infiltrometer, controlled infiltration test

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87 Scale: Micro, Small, Conventional Put a Max Limit on CDA or Require 100% IC in CDA?

88 Rainwater Harvesting

89 Rainwater Harvesting ESD Sizing and Applicability Not a lot of design constraints Spreadsheet available to determine the ESD volume actually captured based on indoor and outdoor demand Rain barrels and cisterns shall be designed to capture at least 0.2 inches of rainfall from the contributing rooftop area. A PE value based on the ESDv captured and treated shall be applied to the contributing rooftop area.

90 Micro-Bioretention CDA should not exceed 0.5 acres Must store at least 75% of ESDv OK for all soil types Temp ponding of 12 inches Filter bed between 2 and 4 feet deep

91 Rain Garden

92 Rain-gardens CDA should not exceed 2000 sf (residential) 10,000 sf (other applications) Must store at least 75% of ESDv Preferred for A & B Soils Restricted for C & D Soils Temp ponding of 6 inches Filter bed between 12 and 18 inches deep No underdrain

93 Grass Channels

94 At least its not a credit anymore!

95 ESD Sizing for Grass Channels The maximum flow velocity for the ESDv shall be less than or equal to 1.0 fps.

96 Grass Channels OK for A, B & C Soils For roads not parking lots Swale length = road length Max slope of 4% * Max ESD flow depth of 4 inches Checkdams or infiltration berms Swale bottom at least 2% of CDA* Max CDA of 1 acre * * applies to all three designs

97 CSN Design Guidelines for Grass Channel 1. Explicitly prohibit for parking Lots 2. Minimum bottom width of 4 feet 3. One foot of restored soil along channel bottom required for C and D soils and mass graded B soils 4. No more than 3% slope in any 50 foot segment (low check dams) 5. May need initial biodegradable geo-fabric 6. Be non-erosive for 10 year storm

98 Wet Swales For C and D Soils Non-residential applications Useful in flat terrain with high water table

99 Wet Swale Sizing Wet swales shall be designed to store at least 75% of the ESDv. A PE value equivalent to the volume captured and treated shall be applied to the contributing drainage area. Assume about 8 to 12 Inches

100 CSN Wet Swale Design Criteria 1. Average dry weather ponding depth no more than 6 inches 2. Max. dry weather ponding of 18 inches 3. Multiple cell system, at least every 50 ft 4. Wetland planting plan (emergent or forested) 5. Have hydraulic capacity for 10 year storm

101 Bio-Swales = Dry Swales

102 Bio-Swale ESD Sizing and Applicability OK for all soil types Follow standard swale criteria Surface area 2% of CDA

103