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Developing TMDLs for Indicator Bacteria in Urban Watersheds

Developing TMDLs for Indicator Bacteria in Urban Watersheds. I. Applicable WQS / Criteria.

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Developing TMDLs for Indicator Bacteria in Urban Watersheds

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  1. Developing TMDLs for Indicator Bacteriain Urban Watersheds

  2. I. Applicable WQS / Criteria EPA Ambient WQC For Bacteria – 1986Freshwater: E. colicol/100 mLSteady-State Geometric Mean 126 Single Sample Maximum*: Designated Beach (75% UCL) 235 Moderate Use (82% UCL) 298 Light Use (90% UCL) 410 Infrequent Use (95% UCL) 576* based on log10 standard deviation = 0.4

  3. Indicator Bacterial Criteria: Freshwater 1 0.9 0.8 Meets Criteria 0.7 0.6 Cumulative Frequency 0.5 Exceeds Criteria 0.4 0.3 0.2 0.1 0 1 1.5 2 2.5 3 3.5 4 E. coli (Log10 col./ 100 mL) Geometric Mean = 126 col / 100 mLLog10 STD = 0.4

  4. Indicator Bacteria Criteria: Freshwater 1 0.9 0.8 0.7 Exceeds Criteria 0.6 Cumulative Frequency 0.5 0.4 0.3 0.2 0.1 0 0 500 1,000 1,500 2,000 2,500 3,000 E. coli (col./100 mL) Geometric Mean = 126 col. / 100 mLLog10 STD = 0.4

  5. Indicator Bacteria Sample Data 1 0.9 0.8 0.7 0.6 Cumulative Frequency 0.5 0.4 0.3 0.2 0.1 0 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 E. coli (col./100 mL) Geometric Mean = 200 col. / 100 mLLog10 STD = 0.8

  6. Reduction Required

  7. Meets Criteria Exceeds Criteria Geometric Mean = 126 col. / 100 mLLog10 STD = 0.4

  8. II. Loading Capacity - TMDL • Rank Ambient Monitoring Data (low to high) • Assign Plotting Position (PP = rank/n) • Overlay Plot on Criteria Frequency Distribution • Calculate Average Percent Reduction

  9. Precip. > 0.25” designated as “Wet” (W)

  10. Plotting Position = Rank / 31

  11. Reduction = (E. coli - Criteria) / E. coli Monitoring < Criteria = 0% Reduction Average Reduction Required: 46%

  12. Sasco Brook Buckley Pond Dam @ Rte.1 TMDL46% Reduction NeededTo Meet Criteria

  13. Urban Watersheds “WET Conditions” • High Percentage of Impervious Surfaces • Rapid Runoff Following Rain Events • Ambient Water Quality Strongly Influenced by StormwaterRunoff Quality • MS4 Permit Developed to Regulate/Manage/Improve Stormwater Quality

  14. Urban Watersheds “DRY Conditions” • High Percentage of Impervious Surfaces • Reduced Infiltration, Poor Retention • Ambient Water Quality Strongly Influenced by Non-PointSources • Some Aspects of MS4 Permit will Reduce NPS Load

  15. Establishing WLA and LAPollutant Sources

  16. III. Load Allocation - LA • Select Data for Critical Baseflow (DRY) Condition • Overlay Plot on Criteria Frequency Distribution • Calculate Average Percent Reduction

  17. Average Reduction Required: 39% Only Data for Dry Weather,Baseflow Condition is used Plotting Position and % ReductionRetained from “All Data” Analysis

  18. Sasco Brook - DRY Buckley Pond Dam @ Rte.1 LA39% Reduction NeededTo Meet Criteria

  19. Load Allocation = 39% reduction Breakout: On-site Septic 39 % reduction Domestic Animal 39 % reduction Natural Wildlife 0.0 % reduction - No (0) allocation to dry weather overflows or illegal connections- Urban Wildlife Management Plan may be required if wildlife population excessive

  20. IV. Waste Load Allocation - WLA • Select Data for Critical Stormflow (WET) Condition • Overlay Plot on Criteria Frequency Distribution • Calculate Average Percent Reduction

  21. 58 % Average Reduction Required: Only Data for Wet Weather,Stormwater Dominated Conditionis used Plotting Position and % ReductionRetained from “All Data” Analysis

  22. Sasco Brook - WET Buckley Pond Dam @ Rte.1 WLA58% Reduction NeededTo Meet Criteria

  23. Waste Load Allocation = 58% reduction Breakout: Stormwater 58 % reduction POTW 0.0 % reduction - No (0) allocation to combined sewer overflows- Disinfection required at POTW during recreation season no additional reduction needed

  24. Sasco Brook Buckley Pond Dam @ Rte.1 TMDL46% Reduction NeededTo Meet Criteria

  25. Sasco Brook - DRY Buckley Pond Dam @ Rte.1 LA39% Reduction NeededTo Meet Criteria

  26. Sasco Brook - WET Buckley Pond Dam @ Rte.1 WLA58% Reduction NeededTo Meet Criteria

  27. V. Margin of Safety - MOS • Implementation will Eliminate Illegal Sources (IllicitConnections, Dry Weather Overflows, CSOs) • Assumes All Bacteria Detected Have Health Risk • Equivalent to Bacteria from Human Sources • 3. BMPs effective under both Critical & Non-Critical Conditions

  28. VI. Implementation • Phase II Stormwater Permit (Minimum Measures GoBeyond End-of-pipe e.g., “pooper scooper” ordinance,runoff management, public education) • Stormwater Management Plans (Opportunity to AddressNuisance Wildlife) • Prioritize/Target Wet/Dry Sources

  29. VII. Monitoring • Percent Reduction Calculated from Empirical CumulativeFrequency Plots Provides Direct Way to Measure Progress • Field Presence Will Result in Higher Awareness of Problemsand opportunities • Obtaining Ambient Water Quality Data Presents FewerLogistical Challenges and is Less Costly than StormwaterOutfall Monitoring

  30. Case Study: Sucker Creek • Drainage Area : 17.2 sq mi • Land Use : 23% urban 40% forested 30% residential 7% other • Features: 2 hobby farms local park trailer park 60% sewered • 303d Listed 1998, 2000, 2002 Basis for Listing 3/10/99 850 col/100 mL 6/15/99 250 col/100 mL 9/20/00 30 col/100 mL 12/3/00 150 col/100 mL

  31. Go to Excel

  32. IMPLEMENTATION

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