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WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2002-XXXX 11 MARLEY COOLING TOWER COMPANY SAN JOAQUIN COUNTY The Basin Plan does not provide a numeric water quality objective for chlorine, but the Basin Plan does contain a narrative toxicity objective. At p.III-9.00 the Basin Plan provides that relative to toxicity: "All waters shall be maintained free of toxic substances in concentrations that produce detrimental physiological responses in human,plant, animal, or aquatic life." At page 1, the USEPA's Technical Support Document for Water Quality-based Toxics Control (TSD)provides that "Where States have not developed chemical specific numeric criteria, States may interpret their narrative standards for specific chemicals by using EPA criteria updated with current quantitative risk values." The TSD fixrther states on page 1 "The integrated approach must include the control of toxics through implementation of the "no toxics" criterion and/or numeric criteria for the parameter of toxicity, the control of individual pollutants for which specific chemical water quality criteria exist in a state's standard, as well as the use of biological criteria. Reliance solely on the chemical specific numeric criteria or the narrative criterion or biological criteria would result in only a partially effective State toxics control program." For determining whether there is reasonable potential for an excursion above this narrative objective, the Regional Board used the second method prescribed by 40 CFR 122.44(d)(vi) for determining reasonable potential, which relies on USEPA criteria and other information. The Regional Board chose this method because USEPA's recommended ambient water quality criteria for chlorine have been developed using methodologies that are subject to public review, as is the individual recommended criteria guidance document. USEPA's ambient water quality criteria for protection of aquatic life are 11 pg/L(ppb) as a 4-day average(chronic) concentration, and 19 gg/L (ppb) as a 1-hour average (acute) concentration for total residual chlorine. Based upon results of monitoring, the Regional Board finds that the discharge does have a reasonable potential to cause or contribute to an in-stream excursion above a water quality objective. This Order includes new maximum daily(0.02 mg/L(ppm)) and average monthly (0.01 mg/1 (ppm)) effluent limitations for residual chlorine based upon the USEPA criteria. Previous Orders did not include effluent limitations for chlorine. The source of chlorine is unknown, therefore it is unknown whether the Discharger can immediately comply with these new limitations. Dechlorination techniques are readily available for interim treatment to maintain complaince with these new limitations. 25. In the past, results of effluent chronic toxicity testing using EPA/600/4-91/002 have indicated sporadic instances of reduced Ceriodaphnia Dubia reproduction. Also, previous Order No. 93-221 included an effluent limitation for acute toxicity. This new Order retains an effluent limitation for acute toxicity, and includes continued monitoring of effluent and receiving water for chronic toxicity. 26. The beneficial uses of the underlying groundwater are municipal and domestic, industrial, and agricultural supply. 27. The pennitted discharge is consistent with the antidegradation provisions of 40 CFR 131.12 and SWRCB Resolution 68-16. Compliance with these requirements will result in the use of best practicable treatment or control of the discharge. The impact on existing water quality will be insignificant.