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Stakeholder Meeting for Proposed Changes to Ohio

Construction General Permit

Jason Fyffe and John MathewsOhio EPA, Division of Surface Water

1. Internal draft (under construction)2. Stakeholder outreach (November)3. Public notice of draft renewal (December/January)

• 45-52 days of public comment period

4. Review comments and incorporate changes (Feb/March)

5. Final package for Ohio EPA director signoff• Includes responsive summary (March)

6. Permit issued April 21, 2018

Construction General Permit (Est. Timeline)

How to provide input:• All input is welcome, but specific, descriptive suggestions

of modification or examples of issues are most helpful.

Send email by December 6, 2017:Jason Fyffe

Ohio EPA, Division of Surface WaterSW Permits

P.O. Box [email protected]

Background of the Construction General Permit (CGP)

• Between 1979 and 1983, the National Urban Runoff Program studied storm water runoff as a significant pollution source. The findings eventually led USEPA to initiate a National Pollutant Discharge Elimination System (NPDES) general permit.


• Ohio’s first Construction General Permit (1992) authorized the discharge of stormwater from construction sites. It largely focused on erosion and sediment control during construction, but also provided a general narrative for controlling storm water and pollutants after construction.


• The CGP requires development of a storm water pollution prevention plan (SWP3) and the implementation of this plan on all sites that disturb 1 acre or greater.

• CGP renewal history• 1992, 2003, 2008, 2013, 2018




Post-construction requirement became more detailed and prescriptive for larger sites by incorporating an approach used by the 1998 WEF Manual of Practice.

Post-Construction (Current Permit)Aspects that apply to all construction sites: “So that receiving stream’s physical, chemical and biological characteristics are protected and stream functions are maintained, post-construction storm water practices shall provide perpetual management of runoff quality and quantity.”• …the SWP3 shall contain a description of the post-

construction BMPs…• Detail drawings and maintenance plans shall be provided

for all post-construction BMPs

Post-Construction (Current Permit)• Large sites require capturing & treating the water quality

volume (WQv = C · P · A / 12)

Post-Construction (Current Permit)• Large sites require capturing & treating the water quality

volume (WQv = C · P · A / 12)

• Offsite mitigation may be authorized

• Redevelopment: 20% WQv or 20% reduced imperviousness• Alternative practices may be approved provided they meet a

tested standard (80% TSS testing using TARP; listed on NJStormwater; Mastep.net)

Post-Construction (Current Permit)• Small sites (<5 - 1ac.) describe measures …storm water

detention structures...open vegetated swales and natural depressions; infiltration of runoff onsite; and sequential systems (which combine several practices).

• The SWP3 shall include an explanation of the technical basis used to select the practices.

There is a variety of local interpretation on this, ranging from doing nothing to application of ineffective practices or application of more effective table 2 practices like bioretention.

Generally the rationale for selecting or how the practices meet the purposes is rarely shown in Storm Water Pollution Prevention Plans.

The Goal of Post-Construction BMPs

• An important goal driving Ohio’s post-construction requirements is the target of providing 80% total suspended solids removal from average annual runoff

• The goal of protecting channels from erosion is also provided through the extended detention of storm water

The Goal of Post-Construction BMPs

Conclusions• This includes both concern for pollutants and the

erosive effects on streams• It has a historic basis• It serves as a useful general target for pollution

treatment goals (though specific watershed problems may require additional treatment approaches)

• Other states also use some form of the 80% TSS target




So after 15 years, the post-construction criteria are being updated.

Original Methodology

The WQv approach for Ohio was adapted in 2003, from from Urban Runoff Quality Management (1998).

The assumptions and methodology have been examined to see if they are still valid and able to meet the goal

Original MethodologyAs documented in Ohio EPA’s Post-Construction Q & A (2007):

WQv Equation and InputsWQv = C · P · A/12, where:

WQv = extended detention volume to be capturedP = 0.75C = watershed runoff coefficientA = contributing drainage area (acres)

Approach endorsed by ASCE to reasonably maximize treatment for water quality.

• Balance retention and readiness• Knee-of-the-curve optimization• NOT flood control

Goal: capture of 80% of TSS (annual basis)

WQv Equation and InputsWQv = C · P · A/12, where:

WQv = extended detention volume to be capturedP = 0.75C = watershed runoff coefficientA = contributing drainage area (acres)

Questions:1. Does this reach the 80% TSS goal?2. Does the precipitation (P) reflect up-to-date rainfall data?3. Is C the most appropriate and relevant way to relate

imperviousness to runoff?

Does This Meet the 80% TSS Goal?• Assuming several BMPs can achieve 90% TSS removal

(wet ED basins, wetland ED basins, bioretention and permeable pavement)

• Then we achieve 80% TSS removal on an annual basis by capturing and treating 90% of annual runoff volume

90% annual runoff volume · 90% treatment efficiency = TSS reduction

0.9 · 0.9 = 0.81 (or 81% TSS removal)

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Does This Meet the 80% TSS Goal?• Assuming several BMPs can achieve 90% TSS removal

(wet ED basins, wetland ED basins, bioretention and permeable pavement)

• Then we achieve 80% TSS removal on an annual basis by capturing and treating 90% of annual runoff volume

90% annual runoff volume · 90% treatment efficiency = TSS reduction

0.9 · 0.9 = 0.81 (81% TSS removal)

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P= 0.75 was estimated to be about 85% of rainfall events and is actually lower (near 80%)

Does Precipitation (P) Reflect Current Rainfall Data & Approaches?

(From figure 5.3 Mean storm precipitation depth. See WEF, 1998 pages 175-177)

Estimated statewide mean = 0.50”24 hr maximized detention multiplier

x (1.582) = 0.80” (range 0.73” to 0.89”)48 hr maximized detention multiplier

x (1.963) = 0.98” (range 0.90” to 1.10”)

Does This Meet the 80% TSS Goal?• Conclusion: The precipitation value needed to be

reviewed and updated

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Is C the Best Volumetric Runoff Coefficient?

• C = 0.858i3 – 0.78i2 + 0.774i + 0.04• Used in Ohio, California and Denver, Colorado

• Rv = 0.05 + 0.9i• More common usage (8 nearby states)

• Rv (impervious) = 0.95• Rv (pervious) = 0.05


Credit: Jay Dorsey


Undisturbed Soils Renovated Soils


Volumetric runoff coefficients (Rv) adjusted for impervious, disturbed soils and natural soils

Battiata, J., K. Collins, D. Hirschman, and G. Hoffman. 2010. The Runoff Reduction Method. J. Contemporary Water Research and Education 146: 11-21.

Potential Changes to the Permit1. Electronic submittal of all plans (SWP3)2. Sediment basins and sediment barriers clarifications3. Update post-construction requirements

A. Capture WQv in a Table 2 practice for all developments > 1 acB. Adjust the WQv Calculation:

i. Change the volumetric runoff coefficient equation (Rv) with options for natural soils or restored soils

ii. Increasing the precipitation value to 0.9 inchesC. Table 2: Add underground detention; full WQv for Wet E-DD. Credit green infrastructure practices that can reduce the WQvE. Redevelopment – reduce imperviousness by 20%; provide 20%

of the WQv with a green infrastructure practice; or provide 40% of the WQv with standard extended detention practices

F. Alternative practices: acceptable testing, PSD and appropriate water quality flow

4. On-site infiltration may be used for Big Darby groundwater recharge

Potential Changes to the Permit1. Request electronic submittal of all plans (SWP3)

Potential Changes to the Permit1. Request electronic submittal of all plans (SWPPP)2. Sediment basins and sediment barrier clarifications

• All sed basins have drain times of 48 hours • (misconception – 48 hr only applied to sites >5 ac)

• Sediment basins are appropriate for sites < 10 ac• (misconception – sed basins only for sites >10 ac)

Potential Changes to the Permit1. Request electronic submittal of all plans (SWPPP)2. Sediment basins and sediment barriers clarifications

• All sed. basins have drain times of 48 hours • Sediment basins are appropriate for sites < 10 ac• Minimum size sediment barrier as replacement for silt fence

“For most applications, standard silt fence is replaced with 12" diameter filter socks.” (Rainwater and Land Development manual, updated 11-6-14. Chapter 6, page 48.

Potential Changes to the Permit1. Request electronic submittal of all plans (SWPPP)2. Sediment basins and sediment barriers clarifications3. Update post-construction requirements


A. Capture WQv in a Table 2 practice for all developments > 1 ac

(3.A.) Post-Construction ChangesCapture WQv in a Table 2 practice for all developments > 1 acRationale:

• Permit states same objectives for large and small sites• Currently small sites have a narrative description of the

requirement while large sites have a standard list of practices• Many small sites have no post-construction or limited

effectiveness practices being implemented• Table 2 practices are appropriate or can be adapted for all sites


A. Capture WQv in a Table 2 practice for all developments > 1 acB. Adjust the WQv calculation:

i. Alter the runoff coefficient with Rv coefficient and options for natural soils or restored soils

ii. Increase the precipitation value to 0.9 inches

WQv = Rv · P · A / 12Change the volumetric runoff coefficient equation (from C to Rv) with options for natural soils or restored soils

Proposed: Rv = 0.00(Anat) + 0.25(Agraded) + 0.95(Aimp)Atotal

Where:Rv = volumetric runoff coefficientAnat = area of pervious, natural ungraded or restored soil (ac.)Agraded = area of pervious cover, graded soils (ac.)Aimp = area of impervious surface (ac.)Atotal = total site area (ac.)

(3.B.i.) Post-Construction Changes

(3.B.i.) Post-Construction Changes

0.00 (full soil profile) If restored

or left natural

0.25Compacted

soils

0.95 Impervious

(3.B.i.) WQv Equation and Inputs: Runoff Coefficient

Proposed: Rv = 0.00(Anat) + 0.25(Agraded) + 0.95(Aimp)Atotal

Where:Rv = Runoff coefficientAnat = area of pervious, natural ungraded or restored soil (ac.)Agraded= area of pervious cover, graded soils (ac.)Aimp = area of impervious surface (ac.)Atotal = total site area (ac.)

Rationale:• Is based on the Rv=0.05 + 0.9i volumetric runoff coefficient• Accounts for effect of compacted soils• At lower levels of imperviousness, it is modified to encourage soil

preservation and soil rehabilitation on construction sites

WQv = Rv * P * A / 12Proposed: Increase the precipitation value (P) to 0.9 inches

(3.B.ii.) Post-Construction Changes

WQv Equation and Inputs: Precipitation

Location of rainfall gages

used in analysis

An analysis of precipitation was

conducted by OSU(to find 90th percentile

storm)


Gauge Location50th

Percentile75th

Percentile80th

Percentile85th

Percentile90th

Percentile95th

Percentile

Akron-Canton Airport 0.32 0.58 0.67 0.81 0.99 1.36

Cincinnati Airport 0.37 0.71 0.82 0.98 1.18 1.64

Cleveland Airport 0.31 0.57 0.67 0.80 1.00 1.33

Columbus Airport 0.34 0.63 0.73 0.87 1.07 1.48

Dayton Airport 0.35 0.65 0.75 0.90 1.12 1.54

Huntington WV Airport 0.35 0.66 0.77 0.93 1.17 1.56

Mansfield Airport 0.33 0.64 0.76 0.90 1.11 1.51

Toledo Airport 0.32 0.61 0.71 0.84 1.02 1.39

Youngstown Airport 0.31 0.58 0.66 0.79 0.98 1.29

Mean 0.33 0.63 0.73 0.87 1.07 1.45

Rainfall event depth distribution (OSU Report, 2017)

WQv Equation and Inputs: PrecipitationOhio requires capture of the WQv in a Table 2 practice. Actual volume captured is greater than the WQv, because of routing in the stormwater management system. So does the existing 0.75 or another value reach the 90th percentile goal?• To better predict the volume treated, a model was used to

quantify the depth captured and treated Table 2 practices (using the USEPA SWMM model)

WQv P Depth (in)

Dry ED Basin%

Wet ED Basin EDv=0.75WQv

%

Wet ED Basin EDv=WQv

%

Perm-Pave %

Bio-retention%

0.75 85.0 82.8 89.4 85.8 88.90.85 88.1 86.3 92.1 87.9 90.60.90 89.0 87.7 93.0 88.9 91.31.00 91.2 89.4 94.3 90.5 92.7

Table: OSU Analysis Volume Captured vs WQv Event Depth


• Proposed: raise the precipitation value to 0.90” in the Water Quality Volume equation

• Rationale:• The previous P value overestimated the amount of annual

runoff being captured• The new value is updated with Ohio’s long term data record

and better methodology• This value is moderate and considers the effect of routing

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(3.B.) Potential Change in WQv

(3.C.) Post-Construction ChangesTable 2 Practices

• Considering raising the requirement for wet extended detention to from 3/4 WQv to 1 WQv

• In order to meet target effectiveness of 80% TSS

• Add underground extended detention with adequate pretreatment

Provide credit values for green infrastructure practices that can reduce the WQv, reduce site runoff and incentivize green infrastructure.

Examples:• Preserving natural soils or restoring soil quality through

compost amendment• Utilizing bioretention• Utilizing grass swales• Disconnecting impervious surfaces

(3.D.) Post-Construction Changes

(3.E.) Post-Construction ChangesRedevelopment

• Previously developed sites –• reduce imperviousness by 20% • provide 20% of the WQv with a green infrastructure

practice• or provide 40% of the WQv with standard extended

detention practices

(3.F.) Post-Construction ChangesAlternative Practices

• Add a form to expedite case-by-case review of proposed alternative post-construction practices.

• Explains infeasibility and that the alternative meets the minimum criteria

• Still requires that alternative practices be tested to show equivalency to Table 2 practices

• (80% TSS and extended detention if not a negligible discharge impact of the discharge)

• Specifies minimum particle size distribution similar to NJ DEP

• NJ DEP reviewed testing or Washington State TAPE testing accepted

• Requests that water quality flow rate be appropriate for the site time of concentration

(4) Big Darby Watershed (Recharge)

• The groundwater recharge requirement may be met by using on-site infiltrating practices (on-site retention).

Vretention = AHSG-A · 0.9”+ AHSG-B · 0.75” + AHSG-C & D · 0.5

Where Volume = retained on-site with infiltrating practices.

Impacted Soils HSG-A HSG-B HSG-C & D

(inches) 0.9 0.75 0.5

Table: Onsite Recharge Depth Requirement


A. Capture WQv in a Table 2 practice for all developments > 1 acB. Adjust the WQv Calculation:

i. Change the volumetric runoff coefficient equation (Rv) with options for natural soils or restored soils

ii. Increasing the precipitation value to 0.9 inchesC. Table 2: Add underground detention; full WQv for Wet E-DD. Credit green infrastructure practices that can reduce the WQvE. Redevelopment – reduce imperviousness by 20%; provide 20%

of the WQv with a green infrastructure practice; or provide 40% of the WQv with standard extended detention practices

F. Alternative practices: acceptable testing, PSD and appropriate water quality flow

4. On-site infiltration may be used for Big Darby groundwater recharge

1. Internal draft (under construction)2. Stakeholder outreach (November)3. Public notice of draft renewal (December/January)

• 45-52 days of public comment period

4. Review comments and incorporate changes (Feb/March)

5. Final package for Ohio EPA director signoff• Includes responsive summary (March)

6. Permit issued April 21, 2018

Construction General Permit (Est. Timeline)

Planned Additions to the RLD Manual

How to provide input:• All input is welcome, but specific, descriptive suggestions

of modification or examples of issues are most helpful.

Send email by December 6, 2017:Jason Fyffe

Ohio EPA, Division of Surface WaterSW Permits

P.O. Box [email protected]

Where to send input:Jason Fyffe

Ohio EPA, Division of Surface WaterStorm Water Section

[email protected]

Following Were Unused Slides

Other States Standards Influencing P value?

CT 80% TSSME 1” (impervious area)MA 90% TSSRI 1.2”VT 80% TSSNJ 80% TSS (1.25”)NY 80% TSS (1 -1.5”)DE 0.8-1.2”MD 0.9/1”PA 85% TSS reductionGA 85% of storms (1.2”)KY 80% of storms (0.75”)MI 1” or 90% of all storms

MN No net incr. in V, TSS and TPIN 1” (Phase 1 cities)WI 80% TSSNC 85% TSS (1 or 1.5”)IA 1.25” recommendedCO 80th percentile eventNM 90th percentile eventND 0.5” from impervious areaCA Retain 85th percentile NE 80% annual runoff volume WA 6 m-24hour or 91% 24 hr

Who Is Using Rv Or An Adaptation?Regionally, some include:

• Fort Wayne & Indianapolis, Indiana*• Nashville & Knox Co.* Tennessee• SE Michigan Council of Governments*• Connecticut, Illinois, Iowa, Maryland*,

Minnesota*, New Hampshire*, New York, North Carolina*, Pennsylvania*, Vermont, Virginia*, West Virginia, Wisconsin

*Reference: Runoff Coefficient Evaluation for Volumetric BMP sizing, California Dept. of Transportation (2015)

Other References: Illinois Urban Manual, IowaDNR, New York State StormwaterManagement Design Manual (section 4.1), Vermont Stormwater Management handbook (Vol.I), Wisconsin Stormwater Manual, West Virginia Stormwater Management & Deigns Guidance Manual (Ch. 3), Metropolitan Nashville – Davidson County StormwaterManagement Manual.

Virginia (Example of Soil Influenced Rv)

VA RRM Module 4 (VDEQ, 2016)