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15 – HSPF TMDL Model Application

15 – HSPF TMDL Model Application. Virginia Tech Biological Systems Engineering Department 2013. Existing Conditions – Understand how the calibrated HSPF model is adjusted to define “existing conditions”

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15 – HSPF TMDL Model Application

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  1. 15 – HSPF TMDL Model Application Virginia Tech Biological Systems Engineering Department 2013

  2. Existing Conditions – Understand how the calibrated HSPF model is adjusted to define “existing conditions” Allocation Scenarios - Review in depth how the Future Conditions model is used to develop allocation scenarios Exercise: Allocation Scenarios MS4 WLA Development – Examine the process for determining a WLA for MS4(s) in the study watershed TMDL & Daily TMDL – Discuss how TMDL model output are used to calculate the TMDL and Daily TMDL Overview/Objectives

  3. Existing Conditions

  4. Existing Conditions Establish “current” conditions in the watershed Use the source breakdown during allocation scenario development

  5. Existing Conditions General Concepts Modify Calibrated Model: Modeling period – compiled, range of conditions Bring land use and loads to current conditions Change VPDES facilities to permitted conditions Change biosolids to maximum anticipated loads Run, Isolating Each Source Use Results to Inform Allocation Development

  6. Existing Conditions: Source Breakdown Separating out direct deposit sources Using the multipliers in EXT SOURCES Separating out land deposit sources ILS can use multiplier PLS may be done in the preprocessing spreadsheet

  7. Existing Conditions: Source Breakdown • Isolate sources • EXT SOURCES Block • MASS-LINK Block

  8. Source Breakdown

  9. Developing Allocation Scenarios

  10. TMDL Allocations: Source Breakdown Use Using the source breakdown analysis in allocation scenarios Identify key contributors Identify what flow conditions accentuate various contributors

  11. TMDL Allocation General Concepts Model first, then check standard Basic watershed process considerations NPS contributions to violation rates Direct deposit contributions to violation rates Strategies Cut straight pipe dischargers 100% Represent point sources at their permitted limits Refrain from cutting wildlife contributions

  12. Allocation Runs Use the source breakdown as starting point Adjust model to reflect future conditions as appropriate Run the model Use PLTGEN to export daily average time series for analysis Compare results to water quality criteria (endpoints) Geo Mean Standard = 126 cfu/100 ml Instantaneous Standard = 235 cfu/100 ml Adjust, run, and repeat

  13. 13 Geometric Mean Geometric mean indicates the central tendancy or “typical” value (<10.5% Violations) Inst. Standard (235 cfu/100 ml) Geo Mean Standard (126 cfu/100 ml) (No Violations)

  14. TMDL Allocations: Direct Deposit Adjustments • NETWORK Block • Adjust multiplier to affect a reduction • Vary based on Impairment

  15. TMDL Allocations: PLS Source Adjustments • MASS-LINK Block • No adjustment to water unit conversion factor • Adjust multiplier to simulate a reduction • Vary based on Land Use • 90% reduction on Cropland & Pasture • 40% reduction on Residential

  16. Exercise: Allocation Scenarios

  17. Allocation Exercise/Discussion • Allocation scenarios for a mystery watershed • Things to consider: • When are the violations occurring? • Under what conditions? • What type of source should be reduced? • How much reduction should be attempted?

  18. Source Breakdown Graph

  19. Source Breakdown for the Exercise

  20. Run 01

  21. Run 09

  22. Run 22

  23. Run 43

  24. Run 72

  25. Results

  26. Post-Exercise Discussion • Five runs typical presentation • What else would you like to see? • What else do you think the stakeholders would like to see? • What would the contractor need to know to do these?

  27. MS4 WLA Determination

  28. 29 MS4 WLA Determination • DRAFT DEQ TMDL WLA Procedures Guidance • Determined using the TMDL model • Includes reductions set during allocation • Considers future growth • Lumped if multiple Determine MS4 areas from available data • Load determined by modeling accumulation & wash-off on transitional and impervious LUs

  29. Determine WLA for MS4(s) • Isolate impervious and transitional LUs within MS4, locality’s jurisdiction, or urbanized area • WLAs for MS4’s can be calculated using the modeled runoff flow multiplied by the bacteria WQS.

  30. Calculating WLAMS4 Typically performed separately from TMDL run Identify applicable areas Adjust ILS areas in SCHEMATIC Block

  31. TMDL & Daily TMDL

  32. TMDL TMDL = LA + WLATotal + MOS • TMDL derived from model output • WLATotal is the sum of WLAs • LA is the difference of TMDL and WLATotal, assuming MOS is implicit

  33. TMDL Calculated from Model Output TMDL Model Output WLATotal TMDL = LA + WLATotal

  34. Daily TMDL TMDL = LA + WLATotal + MOS • TMDL derived from 99th percentile flow and WQS concentration (126 cfu/100ml E. coli) • WLATotal is daily expression of the sum of WLAs • LA is the difference of TMDL and WLATotal, assuming MOS is implicit

  35. Daily TMDL Area at gage & watershed outlet Gage Flow Data (ranked) Geo Mean Standard (126 cfu/100 ml) Daily TMDL Annual TMDL Daily TMDL

  36. Questions?

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