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ODOT OFF-SITE MITIGATION PROGRAM

ODOT OFF-SITE MITIGATION PROGRAM. FOR POST-CONSTRUCTION STORMWATER MANAGEMENT JON PRIER, P.E. - ODNR. ODOT OFF-SITE MITIGATION. Post-Construction BMP Requirements BMP Considerations for Transportation Projects Exfiltration Trench Off-Site Mitigation Requirements

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ODOT OFF-SITE MITIGATION PROGRAM

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  1. ODOT OFF-SITE MITIGATION PROGRAM FOR POST-CONSTRUCTION STORMWATER MANAGEMENT JON PRIER, P.E. - ODNR

  2. ODOT OFF-SITE MITIGATION • Post-Construction BMP Requirements • BMP Considerations for Transportation Projects • Exfiltration Trench • Off-Site Mitigation Requirements • ODOT Off-Site Mitigation Program • Planning for Transportation Projects • Identifying Mitigation Projects • Next Steps

  3. POST-CONSTRUCTION STORMWATER BMP REQUIREMENTS

  4. Post-Construction Requirements • EDA > 1 acre : Quality Treatment • Grass Filter Strip • Wide Grass Swale • Manufactured Device • If New Impervious outside of Existing Right-of-Way > 1 acre : Quantity Treatment • Detention, Retention, Infiltration • Hold Back and Slow Down Runoff to Protect Streams • Quantity Treatment Exclusions: • Redevelopment in 100% Developed Area • Discharging to Fourth Order Stream

  5. BMP CONSIDERATIONS FOR TRANSPORTATION PROJECTS

  6. BMP Considerations • Safety • Traveling Public • Maintenance of BMPs • Limited Right-of-Way

  7. BMP Considerations • ODOT Normally Utilizes: • Vegetated Biofilters • Grass Filter Strips • ODOT sometimes uses Manufactured Systems • These BMPs only Treat Quality (Not Quantity) • Quality: • Removes Sediment by Filtering or Sedimentation • Quantity: • Slows Discharge of Runoff to Protect Stream Stability and Limit Stream Erosion • Detention, Retention, or Infiltration

  8. BMP Considerations • The Following BMPs on Treat Quality and Quantity • Detention • Infiltration • Bioretention • Constructed Wetlands

  9. EXFILTRATION TRENCH

  10. Exfiltration Trench (ExT) • Built into the curb • Pervious concrete • Gravel backfill • Underdrain

  11. ExT Performance • ExT did not Treat Water Quantity • Easily Clogged, Required Frequent Maintenance • Taken out of ODOT L&D Volume 2 on October 18, 2013

  12. Water Quantity Treatment • Previously, ExTs were used to Treat Quantity • To Meet Quantity Requirements: • Detention • Infiltration • Bioretention • Constructed Wetlands • Space Constraints can Limit these BMPs in Urban Areas • Even Underground Detention may be Limited by Utilities within the Right of Way • Off-Site Mitigation

  13. OFF-SITE MITIGATION WHICH PROJECTS QUALIFY? WHAT ARE THE REQUIREMENTS?

  14. Off-Site Mitigation Planning • Determine the On-Site Treatment Requirements • Determine How much can be Treated On-Site • Demonstrate that Full On-Site Treatment is Infeasible

  15. Off-Site Mitigation Planning • Not a Cost / Benefit Assessment • On-Site Treatment is Generally Preferable • Late BMP Planning can Limit Options • Consider Post-Construction BMP Space Requirements Early • The Need for Off-Site Mitigation Should be Identified Early in Project Planning • Ultimately, Ohio EPA Approves Requests for Off-Site Mitigation

  16. Off-Site Mitigation Requirements • Demonstrate Available BMPs are not Feasible • Same HUC-12 Watershed • Mitigation Ratio of 1.5 Times the WQv or the WQv at the Point of Retrofit • Maintenance Agreement to Ensure O&M

  17. ODOT OFF-SITE MITIGATION PROGRAM

  18. Off-Site Mitigation Program Three Phases: • Interim Fee • Short-Term Fee for Projects with Planned ExTs when Removed from ODOT L&D • Pilot Study • Off-Site Mitigation as Defined in Construction General Permit • Long-Term Program • Ongoing Fee In-Lieu Program

  19. Off-Site Mitigation Program Phase 1, Interim Fee: • ~37 ODOT Projects were nearly Finished with Design when ExTs were Removed from L&D • OEPA Set a Temporary Dollar Amount • Reduce Project Schedule Impacts • Funds to be used for Off-Site Mitigation • ODNR / ODOT Identifying Mitigation Partners • Fund Mitigation Projects in the Same Watersheds

  20. Off-Site Mitigation Program Phase 2, Pilot Study: • Match Specific ODOT Project to Specific Mitigation Project • Fees not Defined; Based on Cost of Mitigation • ODNR / ODOT Identifying Mitigation Partners and Specific Mitigation Projects

  21. Off-Site Mitigation Program Phase 3, Long-Term Program: • Methodology for Approving Off-Site Mitigation • Methodology for Coordinating with Mitigation Partners • Especially within other ODOT projects • Documented in ODOT L&D Vol. 2

  22. PLANNING FOR TRANSPORTATION PROJECTS

  23. Plan Early for BMPs • Identify Post-Construction Stormwater BMPs Early in Planning Process • Account for: • BMP Space Requirements • Safety Implications • Maintenance Access and Requirements • Impacts to Flooding • Impacts to Water Quality • Aesthetics • Too Important to Leave Until the End of the Project

  24. Choose the Right BMP for You • Water Quality and/or Quantity • Do you Need to Control Flooding or Limit Stream Erosion? • Do you have other Water Quality Drivers? • Local MS4 Permit, TMDLs, etc. • Balance Capital Costs with Long-Term Maintenance Costs

  25. Consider Off-Site Mitigation • Only if On-Site Treatment is Infeasible • Determine what the Off-Site Requirements are • Look for Mitigation Opportunities • Incorporate Off-Site Mitigation into Project Planning

  26. Plan Holistically • Could One Project go beyond Requirements to Mitigate for a Project with On-Site Limitations? • Take Advantage of Extra Treatment Opportunities when they’re Available. • Off-Site Mitigation is more Expensive when it’s a Stand Alone Project • Less Expensive to Expand Treatment on an Existing Project • Identify both Opportunities and Restrictions

  27. Plan Holistically Identify Mitigation Opportunities: • Available for when Projects May Require Mitigation • Available if ODOT Projects Nearby are Looking for Mitigation

  28. IDENTIFYING MITIGATION PROJECTS

  29. Potential Mitigation Projects • Add-on to Planned Development or BMP • Increase Planned Detention • Treat more than 20% of Redevelopment Area • Retrofit Existing Infrastructure • Detention Basin Forebay, Micropool, and Outlet Structure • Stand Alone Project • Detention, Infiltration, Bioretention, Wetland

  30. Potential Mitigation Projects • Project must: • Treat the Necessary Water Quality Volume or • Demonstrate Equivalent Average Annual Sediment Removal • Project Scale: • Treatment Requirements from Transportation Projects may include WQv from Multiple Acres • Smaller Scale BMPs may not Achieve Enough WQv Treatment • Green Roof • Tree Box • Small-Scale Pervious Pavement

  31. Potential Mitigation Projects Avoid Projects that: • Already have Functioning BMPs • Where Treatment is Already Required • No Double Counting • The Open Space is Committed to Future Development • The BMP would Exacerbate an Existing Flooding Issue

  32. NEXT STEPS

  33. Next Steps – Transportation Projects • Don’t Plan on ExT • Plan Early for Post-Construction BMPs • They Often Require some Space • Weigh the Pros and Cons of Different BMPs • Consider Off-Site Mitigation for Transportation Projects in Urban Areas • Search for Additional Treatment or Mitigation Opportunities in All Projects

  34. QUESTIONS? Jon Prier Natural Resources Engineer ODNR, Soil & Water Resources (614) 265-6680 jon.prier@dnr.state.oh.us

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