SITE INFORMATION AND CORRESPONDENCE 1980-1999

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WASTE DISCHARGE REQUIREMENTS ORDER NO. 5-00- -5- CITY OF LODI WHITE SLOUGH WATER POLLUTION CONTROL PLANT SAN JOAQUIN COUNTY the mixing zone is negligible, and the mixing zone extends for at least 300 meters, the Board will not designate any mixing zone within which water quality objectives will not apply. 23. The Basin Plan water quality objective for cyanide is a maximum concentration of 10 µg/1. EPA's ambient water quality criteria for protection of aquatic life are a continuous concentration of 5.2 µg/1 (30-day average, chronic criteria), and a maximum concentration of 22 µg/1 (1-hour average, acute criteria). Effluent sampling results submitted as part of the application, in studies, and as directed by monitoring and reporting programs show cyanide concentrations have exceeded the EPA acute and chronic criteria, as well as the Basin Plan objective. Background receiving water concentrations of cyanide are unknown, and are presumed to be non-detectable. The Board finds that cyanide is or may be discharged at a level that will cause or have the reasonable potential to cause, or contribute to, an in-stream excursion above the Basin Plan water quality objective. Effluent limitations for cyanide have been included in this Order based on the Basin Plan objective and the chronic criteria, with no mixing zone designated. The Discharger is not currently capable of meeting this limit. 24. The Basin Plan's numerical water quality objective for dissolved zinc is a maximum concentration of 100 µg/l, which is equivalent to a total recoverable concentration of 101 µg/1. EPA's ambient water quality criteria for protection of freshwater aquatic life are a continuous concentration of 117 µg/1 (30-day average, chronic criteria), and a maximum concentration of 118 µg/1 (1-hour average, acute criteria), based on a water hardness of 110 mg/l. These criteria were originally developed using metals concentrations expressed as total recoverable metals, but have been converted to be expressed as dissolved metals. For zinc, the conversion factor(CF) from total to dissolved is CF=0.978 (for acute criteria) and CF=0.986 (for chronic criteria). 40CFR 122.45(c) requires that permit limits be expressed as total recoverable metal. A reasonable assumption is that the metal concentration in the receiving water is biologically available to the same extent as during the toxicity testing. Therefore, the water quality criteria, expressed as dissolved metal, has been divided by the EPA conversion factor, for the purpose of comparing the measured effluent concentrations with the criteria. Sampling results have shown that effluent concentrations of zinc have exceeded the converted acute and chronic criteria, and also the Basin Plan water quality objective if converted to total recoverable metal concentrations of 101 µg/1. The Basin Plan objective is the most stringent. The Board finds that zinc is or may be discharged at a level that will cause or have the reasonable potential to cause, or contribute to, an in-stream excursion above the Basin Plan water quality objective. An effluent limitation for zinc has been included in this Order based on the Basin Plan objective, with no mixing zone designated. The Discharger is not currently capable of meeting this limit. 25. Effluent monitoring for mercury has shown the median concentration to be non-detectable at <0.2 µg/1, and the highest measured to be 0.63 µg/1. The accuracy of the analyses is questionable without implementing `clean technique' for sample collection, handling, and analyses. The current EPA Ambient Water Quality Criteria for continuous concentration of mercury is 0.77 µg/1 (30-day average, chronic criteria), and the proposed California Toxics Rule