SITE INFORMATION AND CORRESPONDENCE 1980-1999

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WASTE DISCHARGE REQSkEMENTS ORDER NO. 2000-**** -5- CITY OF LODI WHITE SLOUGH WATER POLLUTION CONTROL PLANT SAN JOAQUIN COUNTY of 5.2 µg/l (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. 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/l (30-day average, chronic criteria), and a maximum concentration of 118 µg/l (1-hour average, acute criteria), based on a water hardness of 110 mg/1. 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 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. 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/l, 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 concentration is 0.050 µg/1 (chronic criteria). The Sacramento-San Joaquin Delta has been listed as an impaired waterbody pursuant to Section 303(d) of the Clean Water Act because of mercury. This listing is based on elevated levels of mercury in fish tissue. Because the Delta has been listed as an impaired water body for mercury based on fish tissue impairment, the discharge must not cause or contribute to increased mercury levels in fish tissue. In view of the uncertainty of applicable water quality criteria and the accuracy of existing sampling results, this permit does not contain a water quality-based effluent limitation for mercury. This Order requires monitoring for mercury using `ultra-clean technique', for the purpose of establishing a performance-based effluent limitation, if it is determined to be necessary, and allows the Board to reopen the permit to add effluent limits for mercury. In the