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Soil Investigation and Background Groundwater Moniton#ell Installation Workplan January 17,2007 C A M B R I A downstream water rights holders, and water for fisheries and riparian habitat. Downstream of the powerhouse,the Mokelumne River drains into the San Joaquin River that flows to the Sacramento- San Joaquin Delta(the Delta). The powerhouse is located in a rural area surrounded by undeveloped watershed and agricultural land.The Mokelumne River Fish Hatchery is south of the powerhouse located on the southern bank of the Mokelumne River. Twenty-eight miles of the Lower Mokelumne River, from Camanche Reservoir toward the Delta, have been identified as a Water Quality Limited Segment under Section 303(d) of the Clean Water ® Act. Pollutants identified on the California 303(d) list as impairing the Mokelumne River include copper and zinc. Resource extraction is identified as the primary source of these pollutants. The District's discharge from the powerhouse occurs within the copper and zinc impaired region of the Mokelumne River(RWQCB, 2003). Three hydro-powered turbine generators are operated at the Camanche powerhouse and are capable of producing up to 10 million kilowatts of electricity per year for California rate payers.Currently, the power generation process produces industrial wastewater that is treated and discharged from an oil water separation tretention pond to the Mokelumne River at a point south of the pond under Waste Discharge Requirements (WDR) Order No. R5-2003-0153 and National Pollutant Discharge Elimination System(NPDES) permit No. CA0082040. The District is proposing to redirect the existing oil water separation/retention pond's effluent to a 629,000-gallon infiltration/evaporation pond to be constructed on the northwestern corner of the Camanche Warehouse lay down area,approximately 300 feet northwest from the existing discharge point into the Mokelumne River. The final disposal of the discharge would be through infiltration and evaporation (EBMUD,2006). Previous Investigations 2005 Compliance Alternative Study Report&Alternative Selection:On June 27,2005,the District submitted the Compliance Alternatives Study Report that evaluated seven alternatives to comply with strict hardness-based total copper effluent limitations. Land application and effluent limitation modifications concurrent with additional waste stream treatment were the only alternatives that appeared to be feasible (EBMUD, 2005a). On September 27, 2005, the District submitted the Selection of an Alternative far Complying with the Final Copper Effluent Limitations that selected 2