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Future EffluentLimits StudyPAR 1054Metro Wastewater Reclamation District

March 20, 2007

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Agenda

• Project Background• TSD Background• How we used the TSD• Questions

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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

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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

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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

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Project Background

• Modeling Alternatives:– Reduced CBOD discharge limit– Reduced Discharge Flows

• No single strategy worth pursuing

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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)

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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

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TSD Background

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TSD Background

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TSD Background

• Coefficient of Variation:

• TSD allows the use of calculated CVs• TSD allows the use of “default” CV=0.60

Standard Deviation

Mean

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TSD Background

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TSD Background

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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)

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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)

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Questions