Session 2 Strategies to Consider Prior to Retrofits

1. Session 2 Strategies to Consider Prior to Retrofits

2. Session 2 Agenda • Computing Retrofit Sediment and Nutrient Reductions • Design Examples • Cost Effective Strategies that don’t involve traditional retrofits • Specific Methods to document load reductions from non-retrofit practices

3. Computation of Sediment and Nutrient Reductions associated with Retrofits

4. Retrofit Removal Adjustor Curves • Method Developed by CBP Retrofit Expert Panel • In the final stages of adoption by Chesapeake Bay Program (June, 2012) • Tech memo provides technical documentation • Removal rates are a f(x) of runoff depth captured and the amount of stormwater treatment (ST) or runoff reduction (RR) achieved by the retrofit

5. Retrofit Removal Adjustor Curves To determine the amount of runoff depth treated at a site: • Estimate the Runoff Storage volume (RS) available at the site in acre-feet. • Impervious Area (IA) in acres • Input into Standard Retrofit Equation:

9. Design Examples

10. Design Examples – New Retrofit Facility Constructed Wetland • A constructed wetland is built in parkland as a retrofit, classified as a ST practice • The retrofit storage is estimated to be 1.67 acre-feet • Treats runoff from 50 acre residential neighborhood with 40% impervious cover

11. Design Examples – New Retrofit Facility Constructed Wetland • Using the Standard Retrofit Equation: • RS = Retrofit Storage ≈ 1.67 ac-ft • IA = Impervious Area = 20 acres

12. Design Examples – New Retrofit Facility Constructed Wetland Pollutant Removal Efficiencies of the practice

14. BMP Conversion Example • Dry pond conversion • Create new water quality storage using a combination of a forebay with a permanent pool, a submerged gravel wetland cell and a final bioretention polishing cell • New facility now provides a runoff storage volume of 1.3 acre-feet • Treats a site area of 65 acres @ 40% impervious • Classified as a RR practice

15. Design Examples – BMP Conversion • Using the Standard Retrofit Equation: • RS = Retrofit Storage ≈ 1.3 ac-ft • IA = Impervious Area = 26 acres Pollutant Removal Efficiencies of the practice

17. Design Examples – BMP Enhancement • Dry Extended Detention pond sized to capture 0.3” of runoff • 10 acre commercial drainage area @ 100% impervious • Short-circuiting of pond led to half of original storage volume ≈ 0.15”

18. Design Examples – BMP Enhancement • Pond enhanced to: • Increase hydraulic retention time (prevent short-circuiting) • Provide pretreatment • Wetland cells added to bottom of pond in order to provide better treatment • Enhancements recovered 0.15” of lost storage and created additional 0.3” of storage for a combined new storage of: 0.45” per impervious acre

19. Design Examples – BMP Enhancement • Enhancements are slightly different • New removal rates found as the difference between the original rates and the enhanced rates • Original and enhanced rates from the curves • Increase in both runoff volume captured AND runoff reduction capabilities

20. Remember: the site is 100% impervious!!

21. Discussion

22. Cost Effective Strategies that don’t involve traditional retrofits

23. The Changing Stormwater Landscape Under New MS4 Permits and the Chesapeake Bay TMDL ~ 10 to 30% TP and TN load reductions needed from existing development Massive Increase in Retrofitting 15 Years to Get It Done

24. This is inducing a phenomenon known as • “ retrofit stress syndrome” • Infects local public works officials and their elected officials • Common Symptoms: • Fear of the unknown (what exactly is a retrofit?) • Excessive phobia about future costs and regulatory liability

25. Look Beyond the Storage Retrofit…to other Restoration Tools

26. Inoculate Yourself From RSSUsing Other Nutrient Reduction Practices • P Bans and N Fertilizer Mgmt • BMP Maintenance Upgrades • Redevelopment Credits • Watershed Reforestation • Stream Restoration • Street Cleaning • Illicit Discharge Removal • On-site LID Incentives

27. 1. Take credit for fertilizer reductions on urban turf • Reflects recent MD and VA P- Ban in Fertilizer • Modeled as an application reduction on urban pervious area • Initial estimates of 12% TP reduction for urban sector in MARYLAND • Automatic Credit for Localities • Expert Panel to finalize this estimate in summer 2012

28. Urban Nitrogen Fertilizer Reduction • 1.5 million acres of home lawn are fertilized • Same acreage in State WIP Plans • What is Urban Nitrogen Management ? • What are the high risk situations where UNM is most effective? • CBP-approved rates of 17% TN for Urban Nutrient Management is NOT likely to be continued CURRENT EXPERT PANEL

29. Update on Expert Panel on Urban Nitrogen Fertilizer Management • Current CBP-approved rates of 17% TN for Urban Nutrient Management is NOT likely to be continued • N Removal Rate will be Tied to Effectiveness of Local Outreach Efforts to Change Behavior for: • Established Low Risk Lawns • Established High Risk Lawns • New Start Up Lawns • For both lawn care companies and do it yourselfers

30. Urban Nitrogen Management on Public Land • Public land can comprise 10-15% of total turf cover in a community • Fertilizer application rates already tend to be lower • Assess hi risk public lands and change landscaping practices

31. Urban Fertilizer Management Example Panel not ready to define method yet, and the per acre rate may not be very high (2 to 10%), but given that turf comprises 50 to 70% of urban areas, even a small credit could yield impressive benefits More than just brochures!

32. 2. Transform Your Stormwater Maintenance Program Use your stormwater maintenance inspection, tracking and repair budgets to fix problems and boost performance through major maintenance upgrades Potential for both public and private stormwater facilities

33. Design Example – BMP Restoration • Captures 0.5” of runoff from the impervious cover of contributing watershed: 40 acres @ 50% impervious • Sedimentation and invasive plant growth  decreased storage volume by 60% • Only actually provides 0.2” of runoff capture • City conducts major sediment dredging, invasive plant removal, replants pond with natives • Recovers 0.2” of storage for a total storage of 0.4”

34. Design Examples – BMP Restoration If the BMP has previously reported to the state (and already included in CBWM input deck), then the removal rates is determined from the curves as an incremental rate incremental removal rate = restored rates – original rates.

36. 3. Take nutrient reduction credits for more stringent stormwater requirements at redevelopment projects • Calculate the expected acres of impervious cover slated for redevelopment • New CBP tool calculates the aggregate nutrient reduction credit CURRENT EXPERT PANEL

37. Design Examples – Redevelopment A MD developer is redeveloping a 2-acre facility to build a new warehouse. • The pre-development and post-development conditions are 50% impervious and 50% turf land cover. • The BMPs treat the entire site • There are 100% D soils at the site and the site will be developed using RR practices.

38. Design Examples – Redevelopment Using the prescribed method, we calculate the target runoff depth we are controlling for to be: 0.24 inches. • Again, we go to the curves! Pollutant Removal Efficiencies of the practice

40. Individually, load reductions from redevelopment are not impressive But across a community and over 15 years, they can really add up !

41. 4. Watershed Reforestation • Many MD have existing reforestation programs and urban tree canopy goals • Decent load reduction credits are possible for these: • Get extra reduction credit for • Runoff from adjacent IC • Stream buffer upgrades PENDING EXPERT PANEL

42. Qualifying Conditions for Reforestation Credit in MD • Survival rate of 100 trees/acre • 50% of the trees need to be >2” in diameter at 4.5’ above ground • Aggregate of smaller sites is okay • Reforestation done for mitigation purposes is not eligible • Credits are determined as land cover conversion based on the following efficiencies:

43. Load Impacts of Reforestation Adapted from MDE DRAFT Guidance Document 2011

44. Watershed Reforestation Example Bay County reforests 10 acres of turf (pervious land) in a subwatershed Although MDE does not specify how reforestation is converted to equivalent IC Treated, CSN recommends a 10:1 Rule (10 acres reforestation = 1 acre of IC treated, based on runoff relationships)

45. Other Watershed Reforestation Options • Forest Filter Strip* • Urban Stream Buffer* • Urban Tree Canopy** • * Existing EPA-approved rates, new panel to re-evaluate in Fall of 2012 • ** Rate currently being evaluated by expert panel

46. Panel Issues on Tree Planting Credit • Double counting • Is credit immediate or phased in? • Tree mortality • Canopy over Impervious cover • Verification • Tracking • Planting by public and watershed groups

47. 5. Take credit for current and future stream restoration projects • High nutrient reduction rates for qualifying projects • Provides both a local benefit and a Bay benefit • Generally popular with the public • Cost competitive with pond retrofits CURRENT EXPERT PANEL

48. Stream Restoration Removal Rate

49. Stream Restoration • Removal Rate per Linear Foot: • TN = 0.20 lbs • TP = 0.068 lbs • TSS = 310 lbs Qualifying Conditions • Stream reach > 100 ft that is still actively degrading (usually 1st – 3rd order streams) • Comprehensive restoration design: involving channel, banks and floodplain • Special consideration given to projects with floodplain reconnection or in-stream habitat creation

50. Stream Restoration Example MD City opts to restore a 1000’ segment of stream located in a highly urbanized section of the city. Using the removal rates, the City determines the pollutant reduction credits it can take for the project: