SITE INFORMATION AND CORRESPONDENCE

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• i INFORMATION SHEET STOCKTON COGENERATION COMPANY SAN JOAQUIN COUNTY concentrations is 1.0. This means all arsenic measured as total recoverable is to be considered as dissolved when compared to dissolved criteria. Of seven samples collected and analyzed for arsenic biannually between January 1997 and January 2000, all were above the State of California Proposition 65 Regulatory Drinking Water Level of 5 µg/1 for arsenic. Effluent concentrations ranged between 20 and 26 µg/1. Data indicates that the source of the arsenic is the groundwater that is the source for the majority of the cooling tower feedwater. There is no arsenic involved in any part of the SCC operation. Because development of effluent limits will now consider beneficial uses of North Littlejohns Creek and the California Proposition 65 Regulatory Drinking Level has recently been modified, this Order provides for a time schedule for meeting the effluent limitation for arsenic. Molybdenum—The water quality objective 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/1, 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 indicates 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/l has been established in the permit in order to protect agricultural uses of the receiving water. 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/l. 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/l. 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. Total Suspended Solids—A total suspended solids daily maximum limit has been set at 100 mg/l and a monthly average limit of 30 mg/l has been established for discharges from the internal low volume