Future Effluent Limits Study for Metro Wastewater Reclamation District

1. Future Effluent Limits Study PAR 1054 Metro Wastewater Reclamation District March 20, 2007

2. Agenda • Project Background • TSD Background • How we used the TSD • Questions

3. Project Background • Prepare for Metro District’s permit renewal in 2008 • Evaluate proposed ammonia and nitrate limits derived from WQ modeling • Review treatment options used by other WWTPs to meet similar effluent limits. • Limits will drive the scope and timing of infrastructure improvements and operations at the CTP • Evaluate permitting alternatives that • Protect Downstream Uses • Provide Operations Flexibility • Reasonable Monitoring and Compliance Schedule

4. Project Background • Treatment Plant Summaries • Upper Occoquan Sewage Authority (UOSA) – Regional WRF, Centreville, Virginia • Clean Water Services (CWS) – Rock Creek WRF, Hillsboro Oregon • District of Columbia Water and Sewer Authority (DCWASA) – Blue Plains Advanced WWTP, Washington D.C. • Alexandria Sanitation Authority- Advanced Wastewater Treatment Facility (AWTF), Alexandria, Virginia • Stamford Water Pollution Control Authority (WPCA) – Stamford Wastewater Treatment Plant, Stamford, Connecticut

5. Project Background • Treatment Plant Summaries • Stamford Water Pollution Control Authority (WPCA) – Stamford Wastewater Treatment Plant, Stamford, Connecticut • Inland Empire Utilities Agency (IEUA) - Carbon Canyon Water Reclamation Facility (CCWRF), Chino, California • Hampton Roads Sanitation District (HRSD) - Virginia Initiative Plant (VIP), Norfolk, Virginia • City of Calgary - Bonnybrook WWTP, Alberta, Canada • City of Los Angeles -Los Angeles-Glendale Water Reclamation Plant (LAGWRP), Glendale, California • City of Grand Island - Grand Island Wastewater Treatment Facility (GIWWTF), Grand Island, Nebraska

6. Project Background • Modeling Alternatives: • Reduced CBOD discharge limit • Reduced Discharge Flows • No single strategy worth pursuing

7. Project Background • Non-Modeling Alternatives: • Application of human health-based nitrate water quality standards in other states • Federal permitting language that is supportive of a 7-day averaging period for nitrate • Basis for the drinking water standard for nitrate • Well withdrawal of drinking water supplies • Cost comparison for nitrate treatment between water treatment plants and wastewater treatment plants • Statistical basis for longer effluent nitrate concentration compliance periods (TSD)

8. TSD Background • TSD: EPA’s Technical Support Document for Water Quality-based Toxics Control • Technical guidance for assessing and regulating the discharge of toxic substances to surface water • Includes detailed discussion on effluent variability • Provides recommendations for deriving permit limits from wasteload allocations • human health based WQ standards or • water quality modeling

9. TSD Background

10. TSD Background

11. TSD Background • Coefficient of Variation: • TSD allows the use of calculated CVs • TSD allows the use of “default” CV=0.60 Standard Deviation Mean

12. TSD Background

13. TSD Background

14. How we used the TSD • Used Metro Past Effluent data to calculate the Coefficient of Variation • Lower variation for nitrate than CV=0.60 • Slightly higher variation for Ammonia than CV=0.60 • Converted the Human-Health Based Acute Nitrate Wasteload Allocation of 10 mg/L into a (lower) permit limit over longer averaging period • Used 95% prob. for 7-day average (8.68) • Used 99% prob. for 30-day ave. (8.14)

15. How we used the TSD • Converted the WQ Model Acute Ammonia Wasteload Allocation (varies by month) into a (lower) permit limit over longer averaging period • Used 95% probability for 7-day average (Varies monthly minimum is 1.75 in Aug) • Used 99% probability for 30-day average (Varies monthly minimum is 1.46 in Aug)

16. Questions