ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

Home Browse Search

The existing collection system generally serves the developed portions of the city,with major trunk sewers located in the core of the city(i.e.,the central trunk sewer shed),which is approximately bound by SR 120 to the south,Austin Road to the east, Lathrop Road to the north, and Airport Way to the west. Several residential subdivisions located on the perimeter of the City or beyond the central trunk sewer shed have installed temporary wastewater pump stations and facilities to connect to the central trunk shed. Exhibit 3-2 shows the area served by the WQCF and collection system. 3.6.2 HISTORIC WASTEWATER FLOWS Wastewater flows to the Manteca WQCF have steadily increased as the population and commercial and industrial activity in and around the city has grown. Average flows to the plant have increased from just over 4 mgd ADWF in 1991, 5.81 mgd ADWF in 2003, and 6.0 mgd ADWF in December 2005. 3.6.3 EXISTING WASTEWATER TREATMENT FACILITIES, PROCESSES, AND COLLECTION SYSTEM FACILITIES SITE OVERVIEW The existing collection system alignment is shown on Exhibit 3-2 and a detailed layout of the existing WQCF is shown in Exhibit 3-4. The existing WQCF consists of a preliminary,primary, and secondary treatment system; effluent storage and discharge facilities; disinfection facilities; a solids treatment system; and support facilities. The existing wastewater collection system consists of gravity flow pipes that are 6-60 inches in diameter, force mains that are 6-24 inches in diameter, and 13 wastewater pump stations. WASTEWATER TREATMENT PROCESS OVERVIEW The current WQCF is a combined biofilter and activated-sludge plant that treats wastewater using mechanical screening,primary treatment,secondary aeration,settling,chlorine disinfection,and dechlorination. The WQCF treats wastewater to a"secondary level"using a series of mechanical and biological systems to remove wastes. "Secondary level"means that organic wastes are removed by biological treatment with subsequent clarification and disinfection. Small concentrations of contaminants remain in the discharge.Processes employed at the WQCF include raw influent and effluent pumping,primary clarification,aeration and high-rate activated-sludge treatment, disinfection,solids thickening,anaerobic solids digestion, and mechanical dewatering.The treatment processes convert raw wastewater into treated effluent,which is discharged to 190 acres of City-owned agricultural land and the San Joaquin River.A simplified treatment process flow schematic is shown in Exhibit 3-5. EXISTING LIQUID STREAM TREATMENT SYSTEM Preliminary Treatment Wastewater enters the WQCF either via a 54-inch influent trunk sewer(North Manteca Trunk Sewer), or an 18- inch force main(stage 2 force main). Both the trunk sewer and the force main terminate at the influent pump station wet well. The pump station includes two fine mechanical screens, a wet well, a dry well with four centrifugal pumps, and a flow meter. The two fine mechanical screens are designed to remove course solids and nonbiodegradable materials such as plastics. From the wet well,pumps lift screened wastewater to two parallel secondary treatment systems,designated the Northside Facilities(NSF)and the Southside Facilities(SSF). Manteca WQCF and Collection System Master Plans EIR EDAW City of Manteca 3-9 Project Description