SITE INFORMATION AND CORRESPONDENCE 2000-2018

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WASTE DISCHARGE REQUIREMENTS ORDER NO. 5-00-031 -6- CITY OF LODI WHITE SLOUGH WATER POLLUTION CONTROL PLANT SAN JOAQUIN COUNTY 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/l. The Basin Plan objective is the most stringent. The Board finds that zinc is or may be discharged ata 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 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 contains an interim performance-based effluent limit of_ 1.36 lbs/year for mercury. This interim mass limit was developed taking one-half of the average effluent mercury concentration (<0.2 µg/1) and applying that to the average daily flow of 5.6 mgd discharged to Dredger Cut for 8 months out of the year and including a ,20% allowance in mass loading to account for unforeseen variability in concentrations. The limit will not become effective until 1 January 2004, or one year after establishment and approval of a watershed mercury loading offset program. This Order requires monitoring for mercury using `clean technique', and allows the Board to reopen the permit to modify the interim effluent limits for mercury if it is determined to be necessary. In addition, the Discharger is required to develop a program for identification and control of mercury discharged within the collection system. 26. EPA's ambient water quality criteria for protection of aquatic life for a continuous concentration of lead is 3.7 µg/1 (30-day average, chronic criteria), based on a water hardness of 113 me, and as converted to be expressed as total recoverable metal. Effluent monitoring for lead has shown the median concentration to be 1.5 µg/1, and the highest measured to be 10 µg,n, with 3 of 18 samples exceeding the converted chronic criteria. Five of the 18 samples had a relatively high reporting/detection limit of 5.0 µg/l. The Board finds that lead is or may be