Session 2 Strategies to Consider Prior to Retrofits - PowerPoint Presentation

1. Session 2 Strategies to Consider Prior to Retrofits

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

3. Computation of Sediment and Nutrient Reductions associated with Retrofits

4. Retrofit Removal Adjustor CurvesMethod Developed by CBP Retrofit Expert PanelIn the final stages of adoption by Chesapeake Bay Program (June, 2012)Tech memo provides technical documentationRemoval 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 CurvesTo 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 acresInput into Standard Retrofit Equation:

6. Classification of Retrofits Runoff Reduction Practices (RR)Stormwater Treatment Practices (ST)All ESD credits in MD (2009)Constructed WetlandsAll ESD practices in MD (2009)Dry ED PondsBioretentionFiltering Practices Dry SwaleWet Ponds InfiltrationWet Swale

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10. Design Examples

11. Design Examples – New Retrofit Facility Constructed WetlandA constructed wetland is built in parkland as a retrofit, classified as a ST practiceThe retrofit storage is estimated to be 1.67 acre-feetTreats runoff from 50 acre residential neighborhood with 40% impervious cover

12. Design Examples – New Retrofit Facility Constructed WetlandUsing the Standard Retrofit Equation:RS = Retrofit Storage ≈ 1.67 ac-ftIA = Impervious Area = 20 acres

13. TPTNTSS52%33%66%Design Examples – New Retrofit Facility Constructed WetlandPollutant Removal Efficienciesof the practice

14. Determining the Baseline LoadCan calculate the baseline load using the generic state-wide CBWM (version 5.3.0) urban unit loading rates from MDE guidance document:Calculate the number of pervious and impervious acres in the DA,Multiply by the unit loading rates:* Note: these rates may be updated to reflect the most recent version of the CBWM

15. Retrofit Example 1 – Constructed WetlandTotalNitrogenTotalPhosphorusSuspended SedimentPounds/acre/yearTons/acre/yearIMPERVPERVIMPERVPERVIMPERVPERVMDE Loading Rates10.859.432.040.570.460.07Area (acres)20 ac30 ac20 ac30 ac20 ac30 acBaseline Load500 lbs/yr57.9 lbs/yr11.3 tons/yrRemoval Rate33%52%66%Load Removed164 lbs/yr30.1 lbs/yr7.46 tons/yr

16. BMP Conversion ExampleDry pond conversionCreate new water quality storage using a combination of a forebay with a permanent pool, a submerged gravel wetland cell and a final bioretention polishing cellNew facility now provides a runoff storage volume of 1.3 acre-feetTreats a site area of 65 acres @ 40% imperviousClassified as a RR practice

17. Design Examples – BMP ConversionUsing the Standard Retrofit Equation:RS = Retrofit Storage ≈ 1.3 ac-ftIA = Impervious Area = 26 acresTPTNTSS55%55%59%Pollutant Removal Efficienciesof the practice

18. Design Examples – BMP ConversionTPTNTSS55%55%59%Pollutant Removal Efficienciesof the practice

19. Example 2 – BMP ConversionTotalNitrogenTotalPhosphorusSuspended SedimentPounds/acre/yearTons/acre/yearIMPERVPERVIMPERVPERVIMPERVPERVMDE Loading Rates10.859.432.040.570.460.07Area (acres)26 ac39 ac26 ac39 ac26 ac39 acBaseline Load lbs/yr75.3 lbs/yr14.7 tons/yrRemoval Rate55%55%59%Load Removed357.4 lbs/yr41.4 lbs/yr8.67 tons/yr

20. Design Examples – BMP EnhancementDry Extended Detention pond sized to capture 0.3” of runoff10 acre commercial drainage area @ 100% imperviousShort-circuiting of pond led to half of original storage volume ≈ 0.15”

21. Design Examples – BMP EnhancementPond enhanced to:Increase hydraulic retention time (prevent short-circuiting)Provide pretreatmentWetland cells added to bottom of pond in order to provide better treatmentEnhancements recovered 0.15” of lost storage and created additional 0.3” of storage for a combined new storage of: 0.45” per impervious acre

22. Design Examples – BMP EnhancementEnhancements are slightly differentNew removal rates found as the difference between the original rates and the enhanced ratesOriginal and enhanced rates from the curvesIncrease in both runoff volume captured AND runoff reduction capabilitiesTPTNTSSEnhanced Rate39%25%50%Original Rate21%14%28%Incremental Removal Rate18%11%22%

23. Example 3 – BMP EnhancementTotalNitrogenTotalPhosphorusSuspended SedimentPounds/acre/yearTons/acre/yearIMPERVPERVIMPERVPERVIMPERVPERVMDE Loading Rates10.859.432.040.570.460.07Area (acres)10 ac010 ac0-10 ac0-Baseline Load108.5 lbs/yr20.4 lbs/yr4.6 tons/yr Removal Rate11%18%22%Load Removed11.94 lbs/yr3.67 lbs/yr1.01 tons/yrRemember: the site is 100% impervious!!

24. Discussion

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

26. The Changing Stormwater Landscape Under New MS4 Permits and the Chesapeake Bay TMDL ~ 10 to 30% TP and TN load reductions needed from existing developmentMassive Increase in Retrofitting15 Years to Get It Done

27. 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

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

29. Inoculate Yourself From RSSUsing Other Nutrient Reduction PracticesP Bans and N Fertilizer MgmtBMP Maintenance UpgradesRedevelopment CreditsWatershed ReforestationStream RestorationStreet CleaningIllicit Discharge Removal On-site LID Incentives

30. 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

31. 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 Urban NitrogenFertilizer ReductionCURRENT EXPERT PANEL

32. 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 continuedN 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 LawnsFor both lawn care companies and do it yourselfers

33. Basic Outreach Message Mature Lawns, Homeowner MaintainedChoose not to fertilize or apply no more than 2 pounds of N per 1000 square feetMaximize use of slow-release N fertilizer Retain clippings and leaves on the lawn (composting lawn movers) and keep away from streets and storm drainsDo not apply fertilizers before spring green up or after Halloween Do not apply fertilizer within 20 feet of a water feature or within 10 feet of a paved surface Set Mower height at 3 inchesNutrient Reduction Credit Being Evaluated Expert Panel.

34. Targeting Hi Risk Existing Lawns Owners that are currently over-fertilizing (more than 5 lbs N per year) AND ONE OR MORE OF THE FOLLOWING FACTORS * Steep Slopes “Shallow Soils” (Compacted Soils, Karst, Sandy, Hi Water Table) Hi Density Residential or Commercial Land Use Adjacent to River or Bay *Local governments would need to screen for these factors to target outreach efforts, each factor needs to be numerically defined

35. Public land can comprise 10-15% of total turf cover in a community Fertilizer application rates already tend to be lowerAssess hi risk public lands and change landscaping practicesUrban Nitrogen Management on Public Land

36. Relative impact of wholesale vs. retail outreach Defining high risk lawns in your communityFertilization behaviors changes over time – may regress without continued outreach and education programsVerifying actual lawn acreage affectedVerification Problems

37. Urban Fertilizer Management ExamplePanel 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 benefitsMore than just brochures!

38. 2. Transform Your Stormwater Maintenance ProgramUse your stormwater maintenance inspection, tracking and repair budgets to fix problems and boost performance through major maintenance upgradesPotential for both public and private stormwater facilities

39. Design Example – BMP RestorationCaptures 0.5” of runoff from the impervious cover of contributing watershed: 40 acres @ 50% imperviousSedimentation and invasive plant growth  decreased storage volume by 60%Only actually provides 0.2” of runoff captureCity conducts major sediment dredging, invasive plant removal, replants pond with nativesRecovers 0.2” of storage for a total storage of 0.4”

40. Design Examples – BMP RestorationIf 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 rateincremental removal rate = restored rates – original rates. TPTNTSSRestored Rate37%24%47%Original Rate26%16%33%Incremental Removal Rate11%8%14%

41. BMP Restoration ExampleTotalNitrogenTotalPhosphorusSuspended SedimentPounds/acre/yearTons/acre/yearIMPERVPERVIMPERVPERVIMPERVPERVMDELoading Rates10.859.432.040.570.460.07Area (acres)20 ac20 ac20 ac20 ac20 ac20 acBaseline Load405.6 lbs/yr52.3 lbs/yr10.6 tons/yrRemoval Rate8%11%14%Load Removed32.5 lbs/yr5.74 lbs/yr1.49 tons/yr

42. 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

43. Design Examples – RedevelopmentA 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.

44. Design Examples – RedevelopmentUsing the prescribed method, we calculate the target runoff depth we are controlling for to be: 0.24 inches.Again, we go to the curves!TPTNTSS36%37%40%Pollutant Removal Efficienciesof the practice

45. Design Examples – RedevelopmentTPTNTSS36%37%40%Pollutant Removal Efficienciesof the practice

46. Calculating Pollutant Reduction for Redevelopment SiteTotalNitrogenTotalPhosphorusSuspended SedimentPounds/acre/yearTons/acre/yearIMPERVPERVIMPERVPERVIMPERVPERVMDELoading Rates10.859.432.040.570.460.07Area (acres)1.0 ac1.0 ac1.0 ac1.0 ac1.0 ac1.0 acBaseline Load20.3 lbs/yr2.61 lbs/yr0.53 tons/yrRemoval Rate37%36%40% Load Removed7.5 lbs/yr0.94lbs/yr0.21 tons/yr

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

48. 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 4. Watershed ReforestationPENDING EXPERT PANEL

49. Qualifying Conditions for Reforestation Credit in MD Survival rate of 100 trees/acre50% of the trees need to be >2” in diameter at 4.5’ above groundAggregate of smaller sites is okayReforestation done for mitigation purposes is not eligibleCredits are determined as land cover conversion based on the following efficiencies:

50. Load Impacts of ReforestationConversion from (lbs/ac/yr)TN (lbs/ac/yr)TP (lbs/ac/yr)TSS (tons/ac/yr)Urban Pervious9.430.570.07Forest3.160.130.03Load Reduction6.270.440.04Urban Impervious10.852.040.44Forest3.160.130.03Load Reduction7.71.910.41Adapted from MDE DRAFT Guidance Document 2011

51. Watershed Reforestation ExampleBay County reforests 10 acres of turf (pervious land) in a subwatershedMDE Method for Converting Acres Reforested to Equivalent Impervious Cover Treated (acres) PollutantAcres Converted from Turf to Forest 2Load Reduction (lbs/acre/year) 1Total Load ReducedTotal N106.2762.7Total P100.444.4Sediment10808001 Adapted from Table 7 in MDE (2011)2 Additional credit provided when impervious cover is converted to forest 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)

52. Other Watershed Reforestation OptionsForest 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

53. Panel Issues on Tree Planting CreditDouble countingIs credit immediate or phased in?Tree mortalityCanopy over Impervious coverVerificationTrackingPlanting by public and watershed groups

54. 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

55. Stream Restoration Removal RateRemoval rate per Linear foot of Qualifying Stream Restoration SourceTNTPTSSCBP 2005 N=10.02 lbs0.00352.55 lbsNew Interim Rate0.20 lbs0.068 lbs310 lbsExpert PanelProject-Specific Method to Define Rate

56. Stream RestorationQualifying ConditionsStream reach > 100 ft that is still actively degrading (usually 1st – 3rd order streams)Comprehensive restoration design: involving channel, banks and floodplainSpecial consideration given to projects with floodplain reconnection or in-stream habitat creationRemoval Rate per Linear Foot: TN = 0.20 lbsTP = 0.068 lbsTSS = 310 lbs

57. Stream Restoration ExampleMD 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:Removal Rate(lbs/ft)Linear Feet of Restored StreamTotal Removal(lbs)TN0.20 lbs1000’200 lbsTP0.068 lbs1000’68 lbsTSS310 lbs1000’155 TONS

58. Converting to Impervious Acres TreatedIn addition to the above pollutant removal values, the MD City is required to report the impervious acres treated. Which can be determined by the following equation: Impervious acreage treated = 1 acre/100 linear feet of restored stream= 10 acres of impervious cover treated

59. A few expert panel notes 3 part method rather than rate per linear feetNot a license to use urban steam corridor for stormwater treatment

60. 6. Take the Mass Credit for Intensive Street Sweeping Qualifying Frequency and Technology Incentive for Sweeping Crews to Maximize Pickup EXISTING EXPERT PANEL

61. Street SweepingTwo Methods Mass Loading Approach* (Preferred)Qualifying Street Lanes MethodQualifying Conditions:Urban street with high average daily traffic volume located in commercial, industrial, central business, high intensity residentialMinimum frequency of 26 times a year (every 2 weeks)Can be grouped for specific times (i.e., Spring and Fall)Reductions based on sweeping technology: Mechanical << Regenerative/Vacuum

62. Mass Loading ApproachMass of collection measured (tons) at point of disposalStep 1. Determine capacity of sweeperStep 2. Weigh solids collected (in tons)Step 3. Record annual mass collected (tons)Step 4. Convert from tons to pounds of solids (multiply by 2000) and convert to dry weight (factor of 0.7)Step 5. Multiply dry weight by established factors: Lbs of TN = 0.0025 lbs of dry weight solids Lbs of TP = 0.001 lbs of dry weight solids Step 6. Compute TSS reduction credit by multiplying the annual mass of dry weight by a factor of 0.3

63. Street Sweeping Example 1The Mass Loading ApproachMD Community wants to take credit for their street sweeping program. They have a regenerative street sweeper with a hopper capacity of 2 tons. On average they have collected a wet mass of 1.5 tons over the course of the year.

64. Street Sweeping Mass Loading ApproachConvert tons of wet mass into lbs and convert to dry weight: 1.5*2000 = 3000 lbs of street solids (wet) 3000*0.7 = 2100 lbs of street solids (dry)Derive nutrient reductions: 2100*0.0025 = 5.25 lbs of TN 2100 * 0.001 = 2.1 lbs of TP3. Compute TSS Reduction: 2100*0.3 = 630 lbs of TSS

65. Qualifying Street Lanes MethodConvert qualifying lane miles into total impervious cover (acres): Miles swept  feet swept  multiplied by lane width (feet)  divide by 43,560 = acres of street sweptMultiply acres swept by pre-sweeping annual load (simple method): TP = 2.0 lbs/impervious acre/year TN = 15.4 lbs/impervious acre/year

66. Qualifying Street Lanes MethodMultiple pre-sweep baseline load by pick-up factors: Multipliers to Reflect Effect of Street Sweeping on the Baseline Load 1TechnologyTPTNMechanical .04.04Regenerative/Vacuum.06.051 CSN 2011

67. Street Sweeping Example Qualifying Street Lanes MethodOver the past year, local MD community has swept the streets 26 times, with a regenerative street sweeper. The community swept 25 lane miles which included both sides of the street.This is converted to an area: Both sides of the street were swept, so an average width of 20 feet could be used. The lane miles were converted to feet and multiplied the 20’ width, and then divided by 43,560 to get the total acres of street swept in the past year = 60.61 acres.

68. Qualifying Street Lanes Example cont.Multiplying the impervious acreage swept (60.61 acres) by the pre-sweeping annual pollutant load, the community was able to determine their baseline load:Baseline LoadPhosphorus(60.61 ac)(2.0 lbs/ac/yr)= 121.21 lbs/yrNitrogen(60.61 ac)(15.4 lbs/ac/yr) = 933.39 lbs/yr

69. Qualifying Street Lanes Example cont.The MD Community then multiplied the baseline load by the Regenerative Technology factors to get load reductions based on their program:Pollutant Removal LoadsTP121.21 lbs/yr*0.06= 7.27 lbs/yrTN933.39 lbs/yr*0.05= 46.66 lbs/yr

70. Converting Acres Swept vs. Impervious Area TreatedMDE Method for Converting Acres Swept to Equivalent Impervious Cover Treated (acres) PollutantAdjustment Factor Acres SweptEquivalent IC Acres TreatedTP0.0460.612.42TN0.0660.613.64TSS0.1260.617.27Average for all three4.44Source: Table 12 in MDE (2011)

71. 7. Take Credit for Eliminating Illicit DischargesFor chronic and episodic sewage discharges that are physically eliminated from storm drainReduction based on rate of dry weather flow and outfall concentration above background levelsOutfall screening is big part of MS4 permits, so gives credit when screening is nutrient based PENDING EXPERT PANEL

72. Illicit Discharge Detection and EliminationCurrently there is no official process for calculating pollutant reduction credits. IDDE program. Expert Panel planned for 2012 for this topic. In the meantime, CSN’s Technical Bulletin #9 has a recommended process that we can use as a guide…

73. Illicit Discharge Detection and EliminationStep 1. Dry weather flow rate and nutrient concentrations measured at outfallsStep 2. Discharge source trackingStep 3. Monitor flow rate and nutrient concentrations at discharge source prior to and after discharge eliminationStep 4. Follow-up monitoring to confirm nutrient concentrations have returned to background levelsStep 5. Compute the nutrient credit: (daily flow rate)(nutrient conc.)(# of days of discharge) = load reduced

74. 8. Residential LID RetrofitsSubsidies, technical assistance, stormwater utility credits and other incentives to build LID retrofits on private land CURRENT EXPERT PANEL

75. Design Examples – Residential Stewardship IncentivesA MD County creates an incentive program for residential homeowners to install rain gardens on their property and would like to determine the pollutant removal rates associated with such a program.

76. Design Examples – Residential Stewardship IncentivesEach homeowner installs a rain garden to treat 500 ft2 of rooftopIf 100 homeowners participate in the program, treatment can occur for a combined drainage area of 1.15 acres, at 100% impervious. The runoff storage volume associated with the combined retrofits is estimated to be 0.05 acre-feet. Rain gardens are an RR practice

77. Design Examples – Residential Stewardship IncentivesThe amount of runoff volume treated by the rain gardens is calculated using standard retrofit equation:The township engineer uses the curves to estimate the projected removal rates associated with the rain garden incentive program:TPTNTSS52%52%55%

78. Calculating Pollutant Load Reduction of On-site LID IncentivesTotalNitrogenTotalPhosphorusSuspended SedimentPounds/acre/yearTons/acre/yearIMPERVPERVIMPERVPERVIMPERVPERVMDELoading Rates10.859.432.040.570.460.07Area (acres)1.15 ac01.15 ac01.15 ac0Baseline Load12.48 lbs/yr2.35 lbs/yr0.53 tons/yrRemoval Rate52%52%55%Load Removed6.5 lbs/yr1.22 lbs/yr0.30 tons/yr

79. Other On-site Options and more on LID Incentives in Session 4

80. Q & A