Basics of ESD and the New Design Sequence

Basics of ESD and the New Design Sequence

Visit: www. cwp. org/CBSTP 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

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

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

Our Traditional Stormwater BMPs Have Not Worked

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

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

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

Status of Compliance Spreadsheet § § Spreadsheet and Users Guide are available at www. chesapeakestormwater. net Has undergone significant testing Version 2. 0 was released in June, 2010 Version 2. 1 released in July 2010

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

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

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

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

Start By Reducing Clearing and Preserving Highly Permeable Soils

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

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 Environmental Mapping Was Conducted at Site Prior to Layout Natural Areas Were Conserved (e. g. , forests, wetlands, steep slopes, floodplains) Stream, Wetland 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 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 Yes No N/A X X X

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 .

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%)

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

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.

Output From Spreadsheet in this Step % Soil Type A % Soil Type B % Soil Type C % Soil Type D Pre-Developed Condition, RCNwoods 0% 60% 40% 0% 61 New Development Soil Type A ESD Rainfall Target, PE (in) Soil Type B ESD Rainfall Target, PE (in) Soil Type C ESD Rainfall Target, PE (in) Soil Type D ESD Rainfall Target, PE (in) 0. 00 1. 08 0. 72 0. 00 Site ESD Rainfall Target, PE (in) 1. 80 ESD Runoff Depth, QE (in) ESD Runoff Volume, ESDv (cf) 0. 68 93, 567 Required Recharge Volume, Rev (ac-ft) Required Recharge Volume, Rev (cf) 0. 25 10, 812

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.

Permeable Pavements

Alternative Surfaces: Green Roof CSN Tip: Design spec available on CSN website – www. chesapeakestormwater. net

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

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 ESDv from Contributing Direct ESDv Upstream Impervious Received by Practices PE Credit Description Cover (ac) Practice (cf) Practice Specific Parameter(s) Disconnection of Rooftop Runoff (A/B Soils) Up to 1 inch credit provided based upon disconnection flow length. 3 18, 622 Disconnection of Rooftop Runoff (C/D Soils) Up to 1 inch credit provided based upon disconnection flow length. 0 Disconnection of Non-Rooftop Runoff (A/B Soils) Up to 1 inch credit provided based upon disconnection and contributing flow lengths. 0 0 75 Disconnection of Non-Rooftop Runoff (C/D Soils) Up to 1 inch credit provided based upon disconnection and contributing flow lengths. 0 0 Sheetflow to Conservation Areas (A/B Soils) Up to 1 inch credit provided based upon conservation area width. Runoff Enhance PE ESDv Volume d Filter Credit credit Remaini Volume Rev (in) (cf) ng (cf) Flow Path (ft) East/West 0 75 Western Shore 1 10, 346 8, 276 10, 346 0 0 0 150 0. 4 0 0 0 0 1 7, 465 -7, 465 Contributing Disconnection Length (ft) (Impervious) Minimum Width (ft) 0 13437 100

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

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

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

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 PE Credit Description CDIA (ac) Direct ESDv Received from Up by Practice (cf) s (cf) PE credit is based on design volume 0 0 PE credit is based on design volume 5 31, 037 0 0 0 Rain Gardens (A/B Soils) Rain Gardens (C/D Soils) PE = 10" x Surface Area / Drainage Area Bioretention (A/B Soils) Bioretention (C/D Soils) PE = 15" x Surface Area / Drainage Area 5 31, 037 0 PE = 15" x Surface Area / Drainage Area 0 0 Landscape Infiltration PE = 20" x Surface Area / Drainage Area 0 0 Grass Swales (A/B Soils) Grass Swales (C/D Soils) PE = 10" x Surface Area / Drainage Area 0. 8 4, 966 7287 PE = 10" x Surface Area / Drainage Area 0 0 0 0 Bio-swales (A/B PE = 15" x Surface Area / Soils) Drainage Area Bio-swales (C/D PE = 15" x Surface Area / Soils) Drainage Area Wet Swales PE credit is based on design volume Practice Specific Parameter(s) Design Volume (cf) Surface Area (sf) 11, 000 Surface Area (sf) 20, 000 Surface Area (sf) 0 Surface Area (sf) 4, 200 0 Surface Area (sf) 0 Enhance d Filter Volume (cf) Rev (cf) PE ESDv credit (cf) 0. 00 0 0 0 17, 600 Sheetflow to Conservation Areas (A/B Soils) Downstream Practice Depth* (ft) 2. 2 Depth* (ft) 1. 6 1. 02 17, 600 13, 437 0. 00 0 0 0 1. 38 23, 750 7, 287 23, 750 Grass Swales (A/B Soils) 0. 00 0 0 0 0. 49 3, 325 1, 641 3, 325 0. 00 0 0 0 Depth* (ft) 1. 0

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.

Several iterations are needed to get to compliance ESDv Treated (cf) 62, 485 PE achieved (inches) 1. 20 WQv Requirements Met Through Environmental Site Design? YES WQv Remaining? (cf) Entire ESDv Treated Through Environmental Site Design? 0 NO ESDv Remaining? (cf) 31, 082 Rev Requirements Met Through Environmental Site Design? Rev Remaining? (cf) YES 0 Total Rev (cf) 62, 485

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)

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

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

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 Reduced RCN for Type B Soils Reduced RCN for Type C Soils Reduced RCN for Type D Soils 42 63 77 81 Composite Reduced RCN 69 Q (in) CPv Treatment Required (cf) 0. 45 62, 511

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

Note Level 1 and 2 Design for Critical Area Structural Practices Stormwater Ponds (Level 1) Stormwater Ponds (Level 2) Stormwater Wetlands (Level 1) Stormwater Wetlands (Level 2) Stormwater Filtering Systems (Level 1) Stormwater Filtering Systems (Level 2) Stormwater Infiltration (Level 1) Stormwater Infiltration (Level 2) Contributing Direct ESDv from Impervious Received by Upstream Cover (ac) Practice (cf) Practices (cf) 0 0 Treatment Volume (cf) Enhanced Filter Volume (cf) Rev (cf) 0 0 Phosphor Load ous Reducti Removal on Efficiency (lbs/yr) 50% 0. 00 75% 0. 00 0 0 0 60% 0. 00 0 0 0 0 65% 60% 90% 0. 00 Total structural CPv provided CPv Requirement Met? CPv Remaining 0 NO 62, 511 Total Load Reduction (lbs P / year) 24. 12 Total Load Reduction Remaining (lbs P / yr) 0. 00 Total Rev provided (cf) Rev Requirement Met? Rev Remaining? (cf) 62, 485 YES 0

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

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

Solution: Rain gardens or rainwater harvesting

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

Alternative Surfaces and Credits

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

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: Permeable Pavements

Design Scales for Permeable Pavers Micro-Scale Small-Scale Large-Scale Suitable Paver PICP 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 Underdrain? Rare Depending on soils Back up underdrain Design Factor Yes

Comparative Properties of the Three Major Permeable Paver Design Factor Porous Concrete (PC) Scale of Application Small and Large Scale Applications Micro, Small and Large Scale Applications Paver Thickness 5 to 8 inches 3 to 4 inches 3 1/8 inches Design Permeability 10 feet/day 6 feet/day 2 feet/day Construction Cost $ 2. 00 to $6. 50 sf $ 0. 50 to $1. 00/sf $ 5. 00 to $ 10. 00/sf Min Batch Size Porous Asphalt (PA) ~ 500 sf Interlocking Pavers (PICP) 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

Permeable Paver ESD Sizing and Applicability Effective RCNs for Permeable Pavements Hydrologic Soil Group Subbase A B C D 6” 76 84 93 ─ 9” 62 65 77 ─ 12” 40 55 70 ─ 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

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 www. chesapeakestormwater. net

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

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.

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).

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: 2 94 3 92 4 88 6 85 8 77

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

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 ESDv from Contributing Direct ESDv Upstream Impervious Received by Practices PE Credit Description Cover (ac) Practice (cf) Practice Specific Parameter(s) Disconnection of Rooftop Runoff (A/B Soils) Up to 1 inch credit provided based upon disconnection flow length. 3 18, 622 Disconnection of Rooftop Runoff (C/D Soils) Up to 1 inch credit provided based upon disconnection flow length. 0 Disconnection of Non-Rooftop Runoff (A/B Soils) Up to 1 inch credit provided based upon disconnection and contributing flow lengths. 0 0 75 Disconnection of Non-Rooftop Runoff (C/D Soils) Up to 1 inch credit provided based upon disconnection and contributing flow lengths. 0 0 Sheetflow to Conservation Areas (A/B Soils) Up to 1 inch credit provided based upon conservation area width. Runoff Enhance PE ESDv Volume d Filter Credit credit Remaini Volume Rev (in) (cf) ng (cf) Flow Path (ft) East/West 0 75 Western Shore 1 10, 346 8, 276 10, 346 0 0 0 150 0. 4 0 0 0 0 1 7, 465 -7, 465 Contributing Disconnection Length (ft) (Impervious) Minimum Width (ft) 0 13437 100

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

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

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

MDE Simple Disconnection § § § § Min. 15 feet length 10 feet lateral setback to IC Max Filter Path 0 f 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

Rooftop Disconnection MDE Sizing and Applicability Applies to all development types of low to moderate intensity ESD Sizing Factors for Rooftop Disconnection Flow Path Length (ft. ) Western Shore 15 30 45 60 75 Eastern Shore 12 24 36 48 60 PE (in. ) = 0. 2 0. 4 0. 6 0. 8 1. 0

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. ) = 0. 2 0. 4 0. 6 0. 8 1. 0

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

Sheet flow to Conservation Area (CA)

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) = 50 75 100 PE (in. ) = 0. 6 0. 8 1. 0

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

Infiltration Berm

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 ?

CSN Tip: Provide a Credit for Soil Restoration and Reforestation Examples of Qualifying Criteria • 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

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

Design of ESD Micro-Practices

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

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 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 Wet Swales X X Enhanced Filters X X X= may be suitable depending on depth to water table, bedrock and slope

Comparing the Micro-Practices ESD PRACTICE ESD Max Efficiency CDA (sf) Rainwater Harvesting 20+ ~20, 000 Gravel Wetlands ~10 < 1 acre Micro-infiltration 15 500 Rain Garden 10 2, 000 Micro-Bioretention 15 20, 000 Landscape Infiltration 20 20, 000 Grass Swales 10 > 1 acre Bioswales 10 > 1 acre Wet Swales 15 > 1 acre Enhanced Filters ~6 n/a Upgrade Size? Yes No No Yes ? No

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

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

Submerged Gravel Wetland

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

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

Dry Well = Micro-infiltration

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 gravel layers in the bottom of the facility. Assume about 15 inches

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

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

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

Rainwater Harvesting

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.

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

Rain Garden

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

Grass Channels

At least its not a credit anymore!

ESD Sizing for Grass Channels The maximum flow velocity for the ESDv shall be less than or equal to 1. 0 fps.

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

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

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

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

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

Bio-Swales = Dry Swales

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