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Phosphorus limits in NPDES permits

Phosphorus limits in NPDES permits. Steven Weiss, Marco Graziani. Phosphorus Limits: a brief history . 1971 , 1.0 mg/L limit if discharge to special designated waters. (e.g. Lk. Superior Basin) Later - Minn.R. 7065.

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Phosphorus limits in NPDES permits

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  1. Phosphorus limits in NPDES permits Steven Weiss, Marco Graziani

  2. Phosphorus Limits: a brief history • 1971, • 1.0 mg/L limit if discharge to special designated waters. (e.g. Lk. Superior Basin) • Later - Minn.R. 7065 • March 2000, Phosphorus Strategy Introduced “de minimus” concept for new or expanding facilities. • 1973 • 1.0 mg/L limit if discharge is directly to or affects a lake. • Later - Minn.R. 7050.0211 • 1990’s – 2000’s • Research and development of numeric eutrophication standards

  3. Phosphorus Limits: a brief history • 2008 • P Strategy promulgated , existing P limit rules condensed. (Minn.R. 7053.0255) • March 2010 • P Decision Tree - Greater focus on federal regulations (WQBELs) • 2008 • Numeric Lake Eutrophication Standards Adopted • (Minn.R. 7050.0222) • 1st five year permit cycle following rule adoption

  4. Phosphorus Limits: a brief history

  5. Lake Eutrophication Standards Impaired Both cause (TP) and response (Chl-a/Secchi) must exceed Restoration / Effluent Limits Focus shifts primarily to meeting TP – significant progress towards attainment of response criteria

  6. Lake Dischargers • 85% discharge upstream of a lake in MN • Of those 80% are upstream of a nutrient impaired lake • Phosphorus is “persistent” • Not volatile • Build up and wash out

  7. River Eutrophication Standards Not here yet ….but in the near future Assessment both cause (TP) and response (Chl-a/other) must exceed to be impaired Restoration / Effluent Limits TP target – make significant progress towards Chl-a criteria Focus primarily where sufficient Chl-a data exist ~ HUC 8/10 watershed outlets

  8. Water Quality Based Effluent Limits • WQBELs - 40 CFR 122.44 (d)(1)(i) • Required for dischargers with reasonable potential to cause or contribute to an excursion in water quality standards • In Minnesota, RP determined when: • Discharge upstream of P impaired water • No intervening nutrient trap between outfall and resource of concern • Discharge at concentration above ambient WQS

  9. WQBELs – methods • Method dependent on best available data and tools • draft or completed TMDLs • model or analysis developed explicitly for limits • If WWTP is a primary source • limit derived directly from WQ model performance • If among many point sources, • model likely to use aggregate mass to represent multiple facilities • distribute mass among permits

  10. WLA – Categorical Approach • WLA – a type of WQBEL • 1990’s baseline ~ 51 MT • Gross WLA ~ 35.4 • Individual facilities not explicitly represented in Bathtub model. • Categorical approach used to divide gross WLA. • Bigger facilities closer to Lake St. Croix • Greater delivery during summer growing season • Removal more cost effective at larger facilities.

  11. WLA – Categorical Approach • Facilities divided into Categories • Municipals • Design capacity • Type – continuous/controlled discharge • Larger Municipals • greater load reduction potential • Removal generally more cost effective • Generally located closer to Lk. St. Croix • Removal more cost effective at larger facilities.

  12. WLAs – Lake St. Croix TMDL P. 26 TMDL Report

  13. WLAs – Lake St. Croix TMDL

  14. WQBEL – Lake Pepin ex. • 600 MT aggregate load for > 590 point sources • Set restrictive limits: • Where greatest reduction potential is available. • Where most feasible. • Categorized facilities by size and type • Developed mass limits based on categorical concentration and design flow

  15. WQBEL – Lake Pepin ex. Blue Water WWTP AWWDF = 2.0 mgd • categorical concentration = 0.8 mg/L Existing 1.0 mg/L TP limit General Formula: Example:

  16. WQBEL – Lake Pepin ex. Discharge at or below 2,210 kg/yr • Blue Water WWTP • AWWDF – 2.0 mgd • Current actual flow - < 1.0mgd • Conc. Limit 1.0 mg/L • Mass Limit 2,210 kg/yr • What concentration does the facility need to operate at to remain in compliance with both limits?

  17. Excel Tool 2) Monitor Flow and Concentration 1) Enter Data 4) Anticipate future violations based on current performance

  18. But…how low and why? Reduction Minimal reduction set to mitigate future load ↑ TMDL likely to require significant nonpoint↓ Reductions Significant Limits set at or near ambient water quality standard end of pipe TP = 0.1 - 0.03 mg/L % reduction necessary to meet standards Load cap reduction set to mitigate future load ↑ TMDL likely to require some nonpoint↓ Reductions Moderate concentration or mass equivalents TP = 1.0 - 0.3 mg/L % point source contribution to water body

  19. Schedules of Compliance Federal Law (40 CFR 122.2, 40 CFR 122.47) “As soon as possible” 2007 EPA Memo , James Hanlon • Based on time necessary to plan, build and secure funding for treatment option chosen by permittee • May extend beyond 5 year permit – must be justified “ASAP” • May not be based on time required to: • Complete TMDL • Explore UAA Not eligible for: • Facilities able to meet WQBEL • New discharges Most likely for existing dischargers w/ new limits that: • Require additional treatment • Outfall relocation

  20. VarianceMinn. R.  7053.0255 Subp. 4 / 7000.7000 / 7053.0195 • Written request from permittee • Should address all applicable components of Minn.R. 7000.7000 Subp.2. A-H • Fee associated with application • Fee does not guarantee acceptance • When appropriate? • Very high per capita treatment cost • Economic hardship • Not permanent relaxation of limit • Must be reevaluated every three years

  21. Summary • Old Policy – wait for TMDL, then set more restrictive limit if necessary • New Policy – if RP, use best available information to set WQBEL now • Numeric river eutrophication standards in future may require more restrictive limits for select facilities • Examine WQ data • Read the rules

  22. Marco Graziani Marco.Graziani@state.mn.us (651) 757- 2398 Steve Weiss Steven.Weiss@state.mn.us (651) 757- 2814

  23. Point source reduction needed High Chlorophyll-a Standard Current Point source(s) reduced Low All sources reduced Excess Low High Total Phosphorus

  24. Reduction from all sources needed High Chlorophyll-a Standard Current Point source(s) reduced Low All sources reduced Excess Low High Total Phosphorus

  25. Phosphorus Rule (Minn. R. 7053.0255) • New or Expanded – 1.0 mg/L • Directly to or affect a lake – 1.0 mg/L or “fullest practicable extent” – 0.3 mg/L • State discharge restrictions (SDR) • Similar to technology based limits • not a Water Quality Based Effluent Limit (WQBEL)

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