SITE INFORMATION AND CORRESPONDENCE

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INFORMATION SHEET ORDER NO. 5-01-119 (REVISED) -3- STOCKTON COGEN COMPANY SAN JOAQUIN COUNTY others and numerical criteria and guidelines for toxic substances developed by other agencies in determining what numeric effluent limitation will properly implement the narrative toxicity objective. Numerical criteria include, for example,USEPA's 10-6 incremental cancer risk estimate for drinking . water of 0.02 µg/1, the California Office of Environmental Health Hazard Assessment's 10-6 risk level of 0.023 µg/1, USEPA's recommended ambient water quality criterion for protection of human health in waters considered to be potential sources of drinking water of 0.018 µg/l at the 10`risk level,the Proposition 65 limit of 5 µg/l, and the California MCL of 50 µg/1. The Board finds that it is more appropriate to use the MCL of 50 µg/1 in this situation than the cancer risk levels. Therefore, there is no reasonable potential for the effluent to exceed 50 µg/1, and an effluent limit for arsenic is not included in this Order. Molybdenum—The water quality goal for the protection of agricultural use for molybdenum is 10 µg/1 as an annual average. Of seven samples collected and analyzed for molybdenum biannually between January 1997 and January 2000, four samples were at or below 5.0 µg/l, one was 9.0 µg/1, one was 15 µg/1, and one was non-detect with a detection limit of 20 µg/1. The data indicate that there is a reasonable potential for the discharge to cause or contribute to an in-stream excursion above the water quality objective for molybdenum. An annual effluent limit of 10 µg/1 has been established in the permit in order to protect agricultural uses of the receiving water. Based on results of monitoring data, the Discharger is capable of complying with the effluent limitation. Dissolved Oxygen—Previous permits issued for this facility contained a receiving water limitation requiring the discharge to not cause receiving water dissolved oxygen to fall below 5.0 mg/1. However, because the beneficial use of cold freshwater habitat applies to this stream segment, the Basin Plan water quality objective for dissolved oxygen is 7.0 mg/1. It is unknown if the Discharger is currently capable of meeting this receiving water limitation. This Order provides for a time schedule for meeting the receiving water limitation. The Board considers the application of a water quality objective that has never been applied to North Littlejohns Creek as a new interpretation of the Basin Plan. Internal Waste Stream Limitations Internal waste stream limitations listed at 40 CFR Part 423.15 for steam electric power generating facilities are applicable to this facility. Federal regulations require that low volume wastes have effluent limits set within a facility. Low volume waste sources have federal regulations that require the Discharger to monitor and meet effluent limitations for certain constituents. Low volume waste sources include wastewater from wet scrubber air pollution control systems, ion exchange water treatment system,water treatment evaporator blowdown, laboratory and sampling streams, boiler blowdown, floor drains, cooling tower basin cleaning wastes, and recirculating house service water systems. Priority Pollutants - The 126 priority pollutants (Appendix A to 40 CFR Part 423) contained in chemicals added for cooling tower maintenance, except chromium and zinc. Compliance maybe determined by engineering calculations which demonstrate that the regulated pollutants are not detectable in the final discharge by the analytical methods in 40 CFR Part 136.