Big Darby Creek Construction Storm Water Permit

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Big Darby Creek Construction Storm Water Permit

Katherine Fontaine Jennifer Conroy, PE Brian
Tornes, PE Chris Everett, CPG
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AGENDA

• Introduction
• Riparian Setbacks
• Sediment Basins
• Post-Construction Controls
• Groundwater Recharge Requirements

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INTRODUCTION
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INTRODUCTION

• a. Geography
• b. Regulatory Context
• c. Applicability
• d. Major Differences from Statewide Permit
• e. Major Differences from Draft Darby Permit

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Big Darby Creek Watershed

• Big Darby Hydrologic Unit Codes (HUCs)
• 05060001-190 (Headwaters to Sugar Creek)
• -010 (Headwaters to Flat Branch)
• -020 (Flat Branch)
• -030 (Flat Branch to Milford Center)
• -040 (Milford Center to Sugar Run)
• -050 (Buck Run)
• -060 (Robinson Run)
• -070 (Sugar Run)
• 05060001-200 (Sugar Creek to Little Darby Creek)
• -010 (Sugar Run to High Free Pike)
• -020 (High Free Pike to Little Darby)
• 05060001-210 (Little Darby Creek)
• -010 (Head waters to Treacle Creek)
• -020 (Upper Treacle Creek)
• -030 (Proctor Run)
• -040 (Lower Treacle Creek)
• -050 (Treacle Creek to Spring Fork)

www.epa.state.oh.us/dsw/permits/GP_ConstructionSit
eStormWater_Darby.html
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Big Darby Creek Jurisdictions
Counties Townships

• Municipalities
• Columbus
• Darbyville
• Harrisburg
• Hilliard
• Marysville
• Milford Center
• Mechanicsburg
• North Lewisburg
• Orient
• Plain City
• Unionville Center
• West Jefferson
• Woodstock

• Champaign County
• Goshen
• Rush
• Union
• Wayne
• Clark County
• Pleasant
• Franklin County
• Norwich
• Pleasant
• Prairie
• Washington
• Logan County
• Perry
• Zone

• Madison County
• Canaan
• Darby
• Deer Creek
• Fairfield
• Jefferson
• Monroe
• Pike
• Somerford
• Pickaway County
• Darby
• Jackson
• Muhlenberg
• Scioto

• Union County
• Allen
• Darby
• Jerome
• Liberty
• Mills Creek
• Paris
• Union

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Regulatory Context

• Big Darby Creek Storm Water Permit

• Ohio General NPDES Permit No. OHC100001
• Effective 10/27/06
• Expires 10/27/11
• Full text at www.epa.state.oh.us/dsw/permits/
  (47 pp)

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Regulatory Context

• Big Darby Creek Total Maximum Daily Loads (TMDL)
  Document
• A watershed plan to address water quality
  impairments in the Big Darby Creek watershed
• Sedimentation identified as a major cause of
  impairment
• Identifies target concentrations, substrate,
  channel, and riparian conditions for sediment
  TMDLs
• Identifies more stringent construction stormwater
  permit as an implementing measure for achieving
  sediment TMDLs
• Full text at www.epa.state.oh.us/dsw/tmdl/ (327
  pages !)

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Regulatory Context

• Big Darby Accord Area
• Western Franklin County only
• Sewer moratorium
• Environmentally Sensitive Development Area (ESDA)
• Land Use Master Plan
• Big Darby Accord Jurisdictions
• Columbus
• Grove City
• Harrisburg
• Hilliard
• Franklin County
• Brown Township
• Norwich Township
• Pleasant Township
• Prairie Township
• Washington Township

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Applicability

• Geographic
• Big Darby Creek Watershed
• (HUC Units 005060001-190, 200, 210, and 220)
• Activities
• New land disturbing activities gt 1 acre (after
  10/27/06)
• Clearing, grubbing, grading, excavating, filling,
  site dewatering, staging, on-site batch
  operations
• 1 acre threshold applies to larger common plan
  of development and sale
• Discharges
• Stormwater discharges during construction
• Also addresses post-development stormwater
  discharges
• Exceptions for fire-fighting, dewatering,
  waterline flushing, irrigation, condensate

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Major Differences From Statewide Permit

• SWPPP must be submitted with NOI
• Submit NOI/SWPPP 45 days (not 21 days) prior to
  work
• Wait for authorization letter
• No erosivity or TMDL waivers
• Mandatory Riparian Setbacks and Mitigation
  Requirements
• Silt fence allowed as primary control only lt 5
  acres
• Centralized sediment basins required for areas gt
  5 ac (not 10 ac)
• Minimum 134 cy/ac sediment storage (not 67 cy/ac)
• 45 mg/l TSS limit and sampling for sediment
  basins
• No dry detention basins (sites gt 5 acres)
• Groundwater recharge requirements

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Major Differences From Draft Permit

• Wait for authorization letter to begin work
• One set of riparian setback criteria (no
  distinctions by county or drainage area size)
• Site specific riparian setback determinations
  allowed (10 x site-specific bankfull width)
• Stream restoration activities allowed in riparian
  setback zone.
• Post-development Water Quality Volume (WQv)
  calculation same as statewide
• Site specific WQv studies allowed
• Groundwater recharge hotspot activities
  identified
• Groundwater recharge Table 2 added (areas with
  low downward migration potential)

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RIPARIAN SETBACKS
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2. RIPARIAN SETBACKS

• Overview of Requirements
• Setback Determinations
• Mitigation Requirements
• Examples

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Overview of Requirements

• Mandatory setbacks (not recommended)
• No intrusions into setback zones without
  mitigation (except restoration activities)
• No temporary or post-development stormwater
  controls sited in setbacks
• Three-zone mitigation requirements

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Setback Determinations

• Three riparian setback alternatives
• 1. Greatest of
• 100-year FEMA floodplain
• 100 feet on each side of the stream
• W 133(DA 0.43) Where W total setback width
  (both sides)
• DA stream drainage area at project site (mi2)
• 2. W133(DA0.43) 100 feet each side OR
• 10 x site-specific bankfull width 100 feet
  each side
• 3. Attachment B design 100 feet each side
  (low gradient, modified, headwater streams or
  ditches)

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Setback Determinations
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Example Riparian Widths
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Mitigation Requirements

• Three-Zone Mitigation Requirements
• Mitigate in same 14-digit Hydrologic Unit
  (watershed)

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Example Mitigation
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SEDIMENT BASINS
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3. SEDIMENT BASINS

• Drainage Area Threshold
• Sizing Criteria/ Design Considerations
• Discharge and Sampling Requirements

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Drainage Area Threshold

• For sites gt 5 acres disturbed at one time, a
  sediment settling pond is required (statewide
  permit gt 10 acres)
• Cannot rely on silt fence as primary control for
  areas gt 5 acres

• For sites lt 5 acres, smaller basins or sediment
  traps should be used with other controls

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Sizing Criteria

• Minimum of 134 cubic yards of effective sediment
  storage per acre of drainage (statewide permit
  says 67 cy)
• Off-site and undisturbed areas must be included
  in total contributing drainage area
• Divert off-site or undisturbed areas to limit
  size of pond
• Pond lt 5 feet deep gt 21 lengthwidth ratio
• Remove sediment when capacity reduced by 40
  (roughly half the basin depth)

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Size Basins for the Total Drainage Area
Source Ohio EPA
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Baffle to Prevent Short-Circuiting
Source Ohio EPA
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Sediment Pond Design Considerations

• Divert clean water away
• Install diversion ditches to convey water to
  ponds. Low maintenance, better control, dual
  purpose.
• Decrease flow velocity at inlet
• Install the pond in a location that will serve
  all phases (post-construction)
• Good erosion control will help keep sediment out
• Resource ODNR Rainwater and Land Development
  Manual

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During Construction Sediment Erosion Controls

• BMPs for Erosion Controls are 90 to 98 percent
  effective at keeping sediment on a construction
  site
• BMPs for Sediment Controls are 50 to 80 percent
  effective at keeping sediment on a construction
  site
• Therefore, Erosion Control BMPs are preferred
  over Sediment Control BMPs
• Source Ohio EPA

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Erosion Control
Erosion Controls must be installed within 7 days
when the site will remain idle for more than 21
days

• Examples include
• Vegetation
• Mulch (i.e., straw or wood chip mulch)
• Matting or Sod
• Ditch Checks
• Riprap
• Geotextiles

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Discharge and Sampling Requirements

• Target of 45 mg/l Total Suspended Solids (TSS) in
  discharge if gt45 mg/l, modify SWP3 and implement
  new control practice(s) within 10 days and
  resample within 3 days or first rainfall event
  thereafter
• Sampling
• At outfall of each sediment pond
• Identify outfalls by a 3-digit number (001, 002,
  etc.)
• Rainfall event 0.25-inch to 0.75-inch rainfall
  event within a 24-hour period
• Grab sampling
• Within 14 days, or the first rainfall event,
  after disturbance
• Quarterly sampling thereafter
• Retain sampling results onsite and available for
  inspection

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POST CONSTRUCTION CONTROLS
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4. POST-CONSTRUCTION CONTROLS

• Water Quality Volume Requirements
• Approved Water Quality Volume Treatment Methods
• Alternative Methods

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Water Quality Volume Requirements

• Large Construction Activities (5 acres up)
• The structural post-construction BMP must be
  sized to treat the water quality volume (WQv)
• The WQv is calculated by 2 methods
• Using hydrologic simulation with hourly
  precipitation data from local municipality
• Using the following equation
• WQv CPA/12

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Calculating the WQv

• If using the following formula to calculate WQv
• WQv C P A/12
• where
• C Runoff Coefficient
• P Precipitation Depth of 0.75-inches
• A Total Contributing Drainage Area (Acres)
• WQv in units of acre-feet

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Calculating the WQv

• If mixed use, must calculate C using a weighted
  average
• Calculate based on the contributing drainage area
  to the BMP you are designingnot the overall
  value for the development

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Sediment Accumulation

• Add 20 to the WQv for storage of sediment, which
  will accumulate in the structure
• For extended detention basins, this should be
  located within forebays or micropools
• For wet basins and constructed wetlands, add 20
  to the wet pool but not the extended detention
  volume

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How to Treat the WQv (Approved Methods)

• Retention (Wet) Ponds
• Constructed Wetlands
• Infiltration Basins
• Bioretention/Bioswales
• Vegetated Swales Filter Strips
• NO DRY DETENTION BASINS

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Target Drain Times for Structural BMPs
Table 6
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Exclusion of Dry Detention Basins

• Dry Detention Basins are not an alternative
  because
• Accumulated sediments can become resuspended
  during large storm events and wash out of the
  basin
• INFILTRATION basins are OK

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Retention Pond (Wet Basin)
Extended Detention is provided above the wet pool
Extended Detention Volume 0.75 WQv
Permanent Pool (0.75 WQv) (0.20 WQv)
Source Ohio EPA
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Wet Basin Outlet
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Wet Retention Pond with Infiltration
WQv stored in infiltration basin
Flood control volume spills over to separate
retention pool
Source Ohio EPA
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Constructed Wetlands
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Vegetated Swales Filter Strips
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Infiltration Basins
Source Ohio EPA
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Bioretention
Runoff that exceeds the WQv bypasses into storm
drain system
Storage volume in cell below this inlet 1.2
WQv
Source Ohio EPA
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Bioretention
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Alternative Methods

• Demonstrate that WQv is provided within an
  existing structural post-construction BMP on-site
  or regional/local storm water management plan
• Alternative structural post-construction BMPs
• Can request approval from Ohio EPA
• Demonstrate equivalent effectiveness to those in
  Table 6

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Post-Construction Design Considerations

• Local flood control requirements
• Maintenance (access pond drain)
• Forebays and micropools at inlets and outlets
• Low-Impact design of site
• Resources
• ODNR Rainwater and Land Development Manual
• City of Columbus Stormwater Drainage Manual
• ODOT LD Manual, Vol. II
• Stormwater Managers Resource Center
  (www.stormwatercenter.net)

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Small Construction Activities

• Small Construction Activities (gt 1, but lt 5
  acres)
• A structural post-construction BMP must be
  installed (however, no minimum design standards
  are specified)
• Velocity dissipation devices (e.g., riprap) must
  be placed at a discharge culvert for erosion
  control

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GROUNDWATER RECHARGE REQUIREMENTS
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5. GROUNDWATER RECHARGE REQUIREMENTS

• Overview of Requirements
• Recharge Calculations
• Recharge Areas and Tables
• Land Use
• Hot Spot Activities
• Mitigation Requirements
• Example Calculation

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Overview of Requirements

• Purpose ensure post-development recharge
  equals/exceeds pre-development recharge
• Must describe conservation strategies, BMPs, or
  other practices for recharge maintenance
• Protection of open space infiltration areas shall
  be by binding conservation easements
• Must be managed by 3rd party, i.e., local
  government, land trust, homeowners association

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Recharge Calculations

• Pre- and post-development recharge calculated as
  follows
• VreX (AX DreX)/12
• Where
• X land use/hydrologic soil group pair
• VreX annual recharge volume for group X
  (acre-feet)
• DreX total recharge depth, from Tables 1
  or 2 (inches)
• Ax area of land use-soil group X (acres)

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Recharge Areas
Use Table 1 to determine Drex for developments in
light blue areas
Use Table 2 to determine Drex for developments in
dark blue areas
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Recharge Tables
from Part III.G.2.d.i of Ohio EPA Permit No.
OHC100001
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Hydrologic Soil Groups
Soil data obtained from USDA - NRCS http//websoi
lsurvey.nrcs.usda.gov/app/
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Land Use

• Land Uses
• Wood/Forest
• Brush
• Meadow
• Managed Wood
• Pasture
• Row Crop
• Urban Grasses
• Residential (low, medium, high density)
• Commercial
• http//www.epa.state.oh.us/dsw/permits/GP_Construc
  tionSiteStormWater_Darby.html

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Hotspot Activities

• Activities expected to produce storm water runoff
  with elevated concentrations of toxic materials
• Mitigation methods must not present risk of
  groundwater contamination
• Typical land uses and activities
• Vehicle salvage yards
• Recycling facilities
• Vehicle maintenance/service
• Fleet storage
• Industrial facilities
• Bulk terminals
• Marinas
• Hazardous materials generation/storage facilities

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Groundwater Recharge Mitigation

• Only required if post-development recharge volume
  is less than pre-development recharge volume
• Two options available for groundwater recharge
  mitigation
• Convert additional land to higher recharge
  potential land use
• Preferred method
• Must be within 14-digit HUC, 2-mile radius
• Structural and non-structural practices
• Engineered seepage to groundwater
• Structures requiring impermeable liners not
  acceptable

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Example Calculation
Existing land use (row crop) For X
CsA, Hydrologic Soil Group C ACsA 15
acres DreCsA 9.0 inches (from Table 2) VreCsA
(15 acres)(9.0 inches)/12 11.3 acre-ft For X
Ko, Hydrologic Soil Group B/D (assumed to be
D) AKo 72.9 acres DreKo 6.2 inches (from
Table 2) VreKo (72.9 acres)(6.2 inches)/12
37.7 acre-ft Total 49 acre-ft
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Example Calculation (cont.)
Proposed land use (Medium Density Residential, 2
units/acre) For X CsA, Hydrologic Soil Group
C ACsA 15 acres DreCsA 7.8 inches (from
Table 2) VreCsA (15 acres)(7.8 inches)/12
9.8 acre-ft For X Ko, Hydrologic Soil Group
B/D (assumed to be D) AKo 72.9 acres DreKo
7.8 inches (from Table 2) VreKo (72.9
acres)(7.8 inches)/12 47.4 acre-ft Total
57.2 acre-ft (mitigation not required)
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Example Calculation (cont.)
Proposed land use (Medium Density Residential, 4
units/acre) For X CsA, Hydrologic Soil Group
C ACsA 15 acres DreCsA 6.5 inches (from
Table 2) VreCsA (15 acres)(6.5 inches)/12
8.1 acre-ft For X Ko, Hydrologic Soil Group
B/D (assumed to be D) AKo 72.9 acres DreKo
6.5 inches (from Table 2) VreKo (72.9
acres)(6.5 inches)/12 39.5 acre-ft Total
47.6 acre-ft (mitigation required)
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QUESTIONS?
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Contacts

• Burgess Niple [phone]
• Mitchel Strain mstrain_at_burnip.com
• Katherine Fontaine kfontaine_at_burnip.com
• Jennifer Conroy jconroy_at_burnip.com
• Brian Tornes btornes_at_burnip.com
• Chris Everett ceverett_at_burnip.com