Basics of ESD and the New Design Sequence

To learn how you can have access to: Discounted Webcasts

Free One-day design workshopsIntensive master stormwater design seminars

Direct On-site technical assistance Self guided web-based learning modules

Visit: www.cwp.org/CBSTP

Agenda1. 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

Bacteria violations in runoff close streams, beaches and shellfish beds

Pesticides detected in 95% of urban streams and fish tissues sampled

Metals, PCBs and hydrocarbons in tidal sediments

Our traditional stormwater practices have not solved these problems

Piney Branc h - W BPB203A

A v g Pre-dev elopment IBIA v g Dur ing-c ons truc tion IBI

A v g Pos t-dev elopment IBI0

10

20

30

40

50

60

70

80

90

100P

erce

nt o

f Bes

t Pos

sibl

e B

IBI S

core

Ex c ellent

Good

Fair

Poor

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

Environmental Site DesignEnvironmental Site Design

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

.

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 X Natural Areas Were Conserved (e.g., forests, wetlands, steep slopes, floodplains)

XStream, Wetland and Shoreline Buffers Were Reserved XDisturbance of Permeable Soils Was Minimized XNatural Flow Paths Were Maintained Across the Site XBuilding Layout Was Fingerprinted to Reduce Clearing and Grading at Site

XSite Grading Promoted Sheetflow From Impervious Areas to Pervious Ones

XSite Design Was Evaluated to Reduce Creation of Needless Impervious Cover

XSite Design Was Evaluated to Maximize Disconnection of Impervious Cover

XSite Design Was Evaluated to Identify Potential Hotspot Generating Area for Stormwater Treatment

XErosion and Sediment Control Practices and Post Construction Stormwater Management Practices Were Integrated into a Comprehensive Plan

X

Tree Planting Was Used at the Site to Convert Turf Areas into Forest

X

The basic idea is that a compliant plan is one without any no’s (either a yes or not applicable)

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) 38Existing Impervious Surface Area (acres) 0Proposed Impervious Surface Area (acres) 13.8

Existing Imperviousness, Ipre 0.0%Proposed Imperviousness, Ipost 36.3%

Development Category New Development

Rainfall Depth, P (in) 1.0Runoff Coefficient, Rv 0.38Water Quality Volume, WQv (ac-in) 14.32Water Quality Volume, WQv (cf) 51,982

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.

% Soil Type A 0%% Soil Type B 60%% Soil Type C 40%% Soil Type D 0%

Pre-Developed Condition, RCNwoods 61

New DevelopmentSoil Type A ESD Rainfall Target, PE (in) 0.00Soil Type B ESD Rainfall Target, PE (in) 1.08Soil Type C ESD Rainfall Target, PE (in) 0.72Soil Type D ESD Rainfall Target, PE (in) 0.00

Site ESD Rainfall Target, PE (in) 1.80

ESD Runoff Depth, QE (in) 0.68ESD Runoff Volume, ESDv (cf) 93,567

Required Recharge Volume, Rev (ac-ft) 0.25Required Recharge Volume, Rev (cf) 10,812

Output From Spreadsheet in this Step

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

Contributing Drainage Area (ac) Thickness Effective RCN

Green Roof (on Soil Type A) 0Green Roof (on Soil Type B) 0Green Roof (on Soil Type C) 0Green Roof (on Soil Type D) 0Permeable Pavement (Soil Type A) 0Permeable Pavement (Soil Type B) 0Permeable Pavement (Soil Type C) 0

Permeable PavementsPermeable 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

.

Step 6: Select Nonstructural Practices to Treat the ESD Rainfall Target

Nonstructural Practices PE Credit Description

Contributing Impervious Cover (ac)

Direct ESDv Received by Practice (cf)

ESDv from

Upstream Practices

(cf)Practice Specific

Parameter(s)

PE

Credit (in)

ESDv credit (cf)

Runoff Volume Remaining (cf)

Enhanced Filter Volume

(cf)Rev (cf)

Disconnection of Rooftop Runoff (A/B Soils)

Up to 1 inch credit provided based upon disconnection flow

length. 3 18,622 0

Flow Path (ft) East/West

1 10,346 8,276   10,34675Western Shore

Disconnection of Rooftop Runoff (C/D Soils)

Up to 1 inch credit provided based upon disconnection flow

length.   0 0     0 0 0   0

Disconnection of Non-Rooftop Runoff (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)

0.4 0 0   075 150

Disconnection of Non-Rooftop Runoff (C/D Soils)

Up to 1 inch credit provided based upon

disconnection and contributing flow

lengths.   0 0     0 0 0   0

Sheetflow to Conservation Areas (A/B Soils)

Up to 1 inch credit provided based upon

conservation area width.   0 13437

Minimum Width (ft)

  1 7,465 -7,465   7,465100

CSN Tip: Connect CIDA “blobs” with pervious “blobs” on plan and check distances/slopes. OK to aggregate acceptable credits in the spreadsheet

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 Micro-practices 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

Step 7: Select Micro-Scale Practices to Treat the ESD Rainfall Target

Micro-Scale Practices PE Credit Description

CDIA (ac)

Direct ESDv Received

by Practice (cf)

ESDv from UpPractice

s (cf)Practice Specific

Parameter(s) PE

ESDv credit (cf)

Enhanced Filter Volume

(cf) Rev (cf)Downstream

Practice

Rainwater Harvesting

PE credit is based on design volume   0 0

Design Volume (cf)

  0.00 0 0   0   Submerged Gravel Wetlands

PE credit is based on design volume   0 0

Surface Area (sf) Depth* (ft)

0.00 0 0   0    2.2

Micro-Infiltration

PE credit is based on design volume 5 31,037 0

Surface Area (sf) Depth* (ft)

1.02 17,600 13,437   17,600

Sheetflow to Conservation Areas

(A/B Soils)11,000 1.6

Rain Gardens (A/B Soils)

PE = 10" x Surface Area / Drainage Area   0 0

Surface Area (sf)

  0.00 0 0   0   Rain Gardens (C/D Soils)

PE = 10" x Surface Area / Drainage Area   0 0 0   0.00 0 0   0  

Bioretention (A/B Soils)

PE = 15" x Surface Area / Drainage Area 5 31,037 0

Surface Area (sf)

  1.38 23,750 7,287   23,750Grass Swales (A/B

Soils)20,000Bioretention (C/D Soils)

PE = 15" x Surface Area / Drainage Area   0 0     0.00 0 0   0  

Landscape Infiltration

PE = 20" x Surface Area / Drainage Area   0 0

Surface Area (sf)

  0.00 0 0   0  0

Grass Swales (A/B Soils)

PE = 10" x Surface Area / Drainage Area 0.8 4,966 7287

Surface Area (sf)

  0.49 3,325 1,641   3,325  4,200Grass Swales (C/D Soils)

PE = 10" x Surface Area / Drainage Area   0 0 0   0.00 0 0   0  

Bio-swales (A/B Soils)

PE = 15" x Surface Area / Drainage Area   0 0

Surface Area (sf)

  0.00 0 0   0  0Bio-swales (C/D Soils)

PE = 15" x Surface Area / Drainage Area   0 0 0   0.00 0 0   0  

Wet SwalesPE credit is based on design

volume   0 0

Surface Area (sf) Depth* (ft)

0.00 0 0   0  0 1.0

It seems complex, but only a few inputs are needed

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 .

ESDv Treated (cf) 62,485 Total Rev (cf) 62,485

PE 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

Rev Requirements Met Through Environmental Site Design? YES

Rev Remaining? (cf) 0

Several iterations are needed to get to compliance

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 42Reduced RCN for Type B Soils 63Reduced RCN for Type C Soils 77Reduced RCN for Type D Soils 81

Composite Reduced RCN 69

Q (in) 0.45CPv Treatment Required (cf) 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 .

Structural Practices

Contributing Impervious Cover (ac)

Direct ESDv Received by Practice (cf)

ESDv from Upstream

Practices (cf)Treatment

Volume (cf)

Enhanced Filter

Volume (cf) Rev (cf)

Phosphorous

Removal Efficiency

Load Reducti

on (lbs/yr)

Stormwater Ponds (Level 1)   0 0     0 50% 0.00Stormwater Ponds (Level 2)   0 0     0 75% 0.00Stormwater Wetlands (Level 1)   0 0       50% 0.00Stormwater Wetlands (Level 2)   0 0       75% 0.00Stormwater Filtering Systems (Level 1)   0 0     0 60% 0.00Stormwater Filtering Systems (Level 2)   0 0     0 65% 0.00Stormwater Infiltration (Level 1)   0 0       60% 0.00Stormwater Infiltration (Level 2)   0 0       90% 0.00

Total structural CPv provided 0 Total Load Reduction (lbs P / year) 24.12

CPv Requirement Met? NO Total Load Reduction Remaining (lbs P / yr) 0.00CPv Remaining 62,511

Total Rev provided (cf) 62,485Rev Requirement Met? YES

Rev Remaining? (cf) 0

Note Level 1 and 2 Design for Critical Area

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

.

ESD PRACTICE InstallAfter Con.

Avoid or Protect

Do not use as ESC

Restore Soil

Disconnect/Filter credits

X X X X

Permeable Paver X X X XRainwater Harvesting XGravel Wetlands X X X XMicro-infiltration X X X XRain Garden X X X XBioretention X XLandscape Infiltration

X X X X

Grass Swales X XBioswales X XWet Swales X XEnhanced Filters X X X X

CONSTRUCTION CONSTRAINTS FORESD MICRO-PRACTICES

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

Contributing Drainage Area (ac) Thickness Effective RCN

Green Roof (on Soil Type A) 0Green Roof (on Soil Type B) 0Green Roof (on Soil Type C) 0Green Roof (on Soil Type D) 0Permeable Pavement (Soil Type A) 0Permeable Pavement (Soil Type B) 0Permeable Pavement (Soil Type C) 0

Alternative Surfaces: Permeable Pavements

Design Scales for Permeable Pavers

Design Factor

Micro-Scale Small-Scale

Large-Scale

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

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

5 to 8 inches 3 to 4 inches 3 1/8 inches

Design Permeability

10 feet/day 6 feet/day 2 feet/day

ConstructionCost

$ 2.00 to $6.50 sf $ 0.50 to $1.00/sf $ 5.00 to $ 10.00/sf

Min Batch Size

~ 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

Permeable PaverESD 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 atwww.chesapeakestormwater.net

Paver Design ModificationEnhanced 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.): 2 3 4 6 8 Effective RCN: 94 92 88 85 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

.

Step 6: Select Nonstructural Practices to Treat the ESD Rainfall Target

Nonstructural Practices PE Credit Description

Contributing Impervious Cover (ac)

Direct ESDv Received by Practice (cf)

ESDv from

Upstream Practices

(cf)Practice Specific

Parameter(s)

PE

Credit (in)

ESDv credit (cf)

Runoff Volume Remaining (cf)

Enhanced Filter Volume

(cf)Rev (cf)

Disconnection of Rooftop Runoff (A/B Soils)

Up to 1 inch credit provided based upon disconnection flow

length. 3 18,622 0

Flow Path (ft) East/West

1 10,346 8,276   10,34675Western Shore

Disconnection of Rooftop Runoff (C/D Soils)

Up to 1 inch credit provided based upon disconnection flow

length.   0 0     0 0 0   0

Disconnection of Non-Rooftop Runoff (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)

0.4 0 0   075 150

Disconnection of Non-Rooftop Runoff (C/D Soils)

Up to 1 inch credit provided based upon

disconnection and contributing flow

lengths.   0 0     0 0 0   0

Sheetflow to Conservation Areas (A/B Soils)

Up to 1 inch credit provided based upon

conservation area width.   0 13437

Minimum Width (ft)

  1 7,465 -7,465   7,465100

CSN Tip: Connect CIDA “blobs” with pervious “blobs” on plan and check distances/slopes. OK to aggregate acceptable credits in the spreadsheet

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

• 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

Soil Restoration is Not Recommended When::

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 non-

rooftop) 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 DisconnectionMDE 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 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 FiltersSoil 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

ESD PRACTICE HSG A HSG B HSG C HSG DPermeable Paver X X XRainwater Harvesting

X X X X

Submerged Gravel Wetlands

X X

Micro-infiltration X XRain Garden X X XBioretention X X XLandscape Infiltration

X X

Grass Swales X X XBioswales X X X XWet Swales X XEnhanced Filters X XX= may be suitable depending on depth to water table, bedrock and slope

Your HSG’s Determine Which Micro-Practices Are Feasible

Comparing the Micro-Practices ESD PRACTICE ESD

Efficiency Max

CDA (sf)Upgrade

Size?Rainwater Harvesting 20+ ~20,000 YesGravel Wetlands ~10 < 1 acre NoMicro-infiltration 15 500 YesRain Garden 10 2,000 NoMicro-Bioretention 15 20,000 YesLandscape Infiltration

20 20,000 No

Grass Swales 10 > 1 acre NoBioswales 10 > 1 acre YesWet Swales 15 > 1 acre ?Enhanced Filters ~6 n/a No

Landscape Infiltration

.

Four layer System

Surface ponding12 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 and 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

Put a Max Limit on CDA or Require 100% IC in CDA?

Scale: Micro, Small, Conventional

Rainwater Harvesting

Rainwater HarvestingESD 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. Explicitly prohibit for parking Lots2. Minimum bottom width of 4 feet3. 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

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

table

Wet SwaleSizing

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. Average dry weather ponding depth no more than 6 inches

2. Max. dry weather ponding of 18 inches3. Multiple cell system, at least every 50 ft4. Wetland planting plan (emergent or

forested) 5. 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