ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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PROPOSED SOLIDS STREAM TREATMENT FACILITIES Solids Thickening and Digestion Wastewater sludge generated in the primary sedimentation basins and activated-sludge process would be anaerobically digested in five new anaerobic digesters. Sizing of the new digesters is based on solids loading and hydraulic detention time criteria. The sludge heating process in the new digesters would be similar to the heating process for the existing digesters. Sludge would be drawn off the digester mixing pipeline with a booster pump, conveyed through a spiral heat exchanger, and discharged back into the mixing pipeline. Solids Dewatering and Disposal Anaerobically digested sludge would be dewatered in a new high-solid centrifuge unit. The new unit would be installed in a new dewatering building designed to accommodate two 100-horsepower centrifuges with space for one additional centrifuge unit in the future. Dewatered cake from the centrifuges would be discharged at a solids content of approximately 30-50%onto a solids handling conveyor. The conveyor would discharge cake outside the building to a biosolids composting and storage area. PROPOSED SUPPORT WASTEWATER QUALITY CONTROL FACILITIES A chemical handling, storage, and metering facility would be required to support the tertiary filtration process as coagulant and polymer may be needed occasionally for filter aids (Exhibit 3-6). The equipment in the facility would include four bulk tanks and one day tank for coagulant,metering pumps, space for four polymer tanks or totes, and a polymer dilution unit. All tanks and pumps would be installed indoors to prevent damage from sunlight and temperature extremes. Cogeneration Solids removed during the wastewater treatment process (i.e., sludge)are stabilized through anaerobic digestion before dewatering and disposal off-site. Methane gas produced during anaerobic digestion is currently either used as a fuel to heat WQCF digesters and maintain sludge temperatures, or is flared under controlled conditions. As an alternative to flaring, digester gas can be scrubbed,blended with natural gas, and routed to an engine generator for electricity production. This electricity could off-set electrical deliveries from PG&E. One cogeneration unit (engine generator) is currently installed at the WQCF but has not yet been brought on-line. Operation of the initial cogeneration unit is anticipated in 2007. Ultimately,three cogeneration units would be installed at WQCF buildout(Richard,pers. comm.,2006a). 3.7.3 PROPOSED WASTEWATER COLLECTION SYSTEM IMPROVEMENTS The proposed project would incrementally add new trunk sewer segments to meet the development goals adopted in the City of Manteca General Plan 2023. Building upon the existing collection system, a trunk sewer gravity collection system would convey wastewater to an influent pump station located at the WQCF. Interim pump stations would be constructed as needed and then gradually phased out as the trunk sewers are completed. The principal objective of the trunk sewer network is to maximize the area of gravity sewer service within the city. Completion of the trunk sewer system would largely eliminate permanent pumping stations within the city with the exception of areas at the limits of the service boundaries. Currently, only one permanent pumping station is anticipated: Southwest Manteca(at the westerly terminus of Woodward Avenue). Several interim pumping stations may be needed depending on the completion schedule of the north and south Manteca trunk sewers. Both the interim and permanent pumping stations would be wet-well/dry-well or submersible configurations, and would be predominantly below grade. The above-grade profile would be limited to an access structure, emergency generator,paved parking area and security fencing. Landscaping would be provided as a visual buffer along with EDAW Manteca WQCF and Collection System Master Plans EIR Project Description 3-22 City of Manteca