SITE INFORMATION AND CORRESPONDENCE

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INFORMATION SHEET ORDER NO. 5-01-119 (REVISED) -2- STOCKTON COGEN COMPANY SAN JOAQUIN COUNTY Effluent/Receiving Water Limitations Total Dissolved Solids - The TDS secondary drinking water MCL is the basis for the effluent limitations of 500 mg/1 as a monthly average and 1000 mg/1 as a daily maximum in Order No. 95-148. These limitations will be unchanged in this version of the permit. For protection of the agricultural supply beneficial use based on crop tolerance, a recommended water quality goal is 450 mg/1 as an annual average. The Board must consider the factors in Water Code Section 13263, including considering the provisions of Water Code Section 13241, in adopting TDS.limitations using the water quality goal. Cost estimates submitted by the Discharger indicate that water use would increase by 31% and costs by $250,000 per year. Also, no agricultural intakes are present downstream of the discharge in North Littlejohns Creek. Therefore, it is more appropriate to use the secondary MCL as the basis for the effluent limitations for TDS. Chlorine Residual—The chlorine residual effluent limitations have been modified from the previous permit. A chlorine residual monthly average limit of 0.01 mg/l and a daily maximum effluent limit of 0.02 mg/1 have been added to the permit in order to protect freshwater aquatic life. It is unknown if the Discharger is currently capable of meeting this effluent limitations. This Order provides for a time schedule for meeting the effluent limitations. The Board considers the application of a water quality objective that has never been applied to North Littlejohn Creek as a new interpretation of the Basin Plan. Copper-Based on a worst-case effluent hardness of 95 mg/l as CaCO3, the CTR hardness dependent copper water quality criteria for protection of aquatic life is 8.6 µg/l as a four day average and 13 µg/l as a 1 hour average. Of seven samples collected biannually between January 1997 and January 2000 the two samples collected in 1998 were both above detection limits at 30 and 50 µg/l. These higher copper concentrations were attributed to process changes in the Discharger's cooling tower disinfection system implemented that year. Once the impact of these process changes on effluent copper concentrations was discovered, the disinfection system was adjusted to reduce copper concentrations below detection limits again. Because of the process changes made to prevent these increased copper concentrations, the Board does not find these to be indicative of reasonable potential. However, the other five samples were below detection limits with four of the five having detection limits ranging between 10 and 30 µg/1. These levels are above the most stringent copper water quality criteria. The fifth of the non-detect samples was at a 4 gg/1 detection level. Based on the fact that all but one of the samples had detection limits higher than the most stringent CTR criteria, more data with appropriate detection limits will be required per SIP section 2.2.2.A. The Discharger is required to develop a workplan and conduct sampling with detection limits low enough to allow for evaluation with the CTR criteria. Arsenic - Arsenic is an inorganic priority pollutant that produces human health effects. Of seven samples collected and analyzed for arsenic biannually between January 1997 and January 2000, all were above the State of California Proposition 65 Level of 5 µg/l for arsenic. Effluent concentrations ranged between 20 and 26 µg/l. Data indicate that the source of the arsenic is the groundwater that is the supply for the majority of the cooling tower feedwater. There is no arsenic added in any part of the SCC . operation. The Basin Plan requires the Board to consider information submitted by the discharger and