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• INFORMATION SHEET COUNTY OF SAN JOAQUIN COUNTY SERVICE AREA NO. 31 FLAG CITY WASTEWATER TREATMENT FACILITY SAN JOAQUIN COUNTY San Joaquin County Service Area(CSA)No. 31 provides wastewater treatment and disposal services for a commercial development along the junction of Interstate 5 and State Route 12. Surface water drainage is to Dredger Cut which is tributary to White Slough. Flag City Wastewater Treatment Plant has been operating under a National Pollutant Discharge Elimination System (NPDES) permit adopted by the Board on 27 March 1992. This permit prescribes requirements for the treatment of domestic wastewater and surface water discharge of treated effluent from the Flag City commercial development. Growth of the development has been slow, and influent flows comprise only a fraction of the plant's design flow of 0.16 million gallons per day (mgd). The Discharger has been operating the plant as a continuous flow extended aeration activated sludge facility, which is better for handling low hydraulic and organic loading conditions. Although the permit regulates a discharge to Highline Canal, since plant startup in late 1995, disposal has been to an evaporation and percolation (EP)pond. This pond was originally intended to be used as an emergency pond, but because of the extremely light hydraulic and organic loading,the plant could not reliably produce effluent to meet permit limitations for a surface water discharge. With Discharger concurrence,Board staff have recommended that waste discharge requirements be adopted in place of the NPDES permit until the land discharge capability is exhausted. The Discharger will apply to the Board for another NPDES permit at least six months before the time that surface water discharge arrangements are needed. An engineered report shall be submitted six (6) months from the date of adoption of this Order that provides the basis for timing of the permit application submittal. The report shall contain a pond capacity evaluation, an analysis demonstrating that all land discharge options will be exhausted, and a proposed flow rate that will trigger submittal of the NPDES permit application. The wastewater treatment and disposal facilities consist of extended aeration activated sludge processing, clarification in a"clarator" unit, and sand filtration before disposal to the 2.24 million gallon EP pond. The Discharger discharges an average of 0.0145 mgd of treated wastewater to the EP pond. Waste activated sludge solids are stabilized by aerobic digestion,then dewatered in a"Draimad"unit, which introduces an organic polymer to the solids as they are deposited into hanging porous plastic bags. The filtrate that drains from the biosolids is returned to the headworks. The bagged solids are further dried by air,then stacked in a covered metal storage unit. Ultimate disposal after testing is by landfilling.