ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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Local Water Supplies The City of Manteca currently provides domestic water to its customers through a network of wells and transmission lines that extract groundwater from underlying aquifers and distribute the water throughout the City. The City recently began receiving domestic water supplies from the SSJID's South County Surface Water Supply Project(SCSWSP),which conveys surface water to the City for municipal use. The SCSWSP is a joint project between SSJID and the Cities of Manteca,Lathrop,Escalon,and Tracy to supply treated potable water to these cities. The SCSWSP involves the operation of a new surface water treatment plant near Woodward Reservoir in Stanislaus County and a 36.5-mile water transmission pipeline with pumping facilities to transport treated water to turnouts at each city. The SCSWSP began supplying surface water supplies to the City of Manteca in 2005 and is expected to provide sufficient surface water supplies to meet the City's future water demands. For additional information regarding local water supplies,the SCSWSP, and groundwater pumping, see Section 4.10, "Public Services and Utilities." WATER QUALITY National Drinking Water Standards (Maximum Contaminant Levels) National drinking water standards include primary and secondary drinking water standards. Drinking water contaminant levels are reported as Maximum Contaminant Levels(MCLS). MCLS are legally enforceable standards based on health risk or nonhealth concerns such as odor or taste.National Primary Drinking Water Regulations(NPDWRs or primary standards) are legally enforceable standards that apply to public water systems. Primary standards protect public health by limiting the levels of contaminants in drinking water.National Secondary Drinking Water Regulations (NSDWRs or secondary standards) are nonenforceable guidelines regulating contaminants that may cause cosmetic effects(such as skin or tooth discoloration)or aesthetic effects (such as taste, odor,or color) in drinking water. The United States EPA recommends secondary standards to water systems but does not require systems to comply. However, states may choose to adopt them as enforceable standards. Groundwater Quality The City's wells currently produce groundwater that meets or exceeds the State Department of Health Services (DHS)recommended drinking water quality standards (City of Manteca 2003a). Some areas of the City's groundwater basin are subject to saltwater intrusion from the Delta and adverse water quality impacts from infiltration of area runoff from urban and agricultural areas. Saline intrusion is the possible result of excessive groundwater withdrawal from aquifers. The extent of saline intrusion in the Manteca area is not well defined but is known to be located west of the City of Lathrop. Saline intrusion is an important issue related to the reliability of the existing groundwater system as it could result in well abandonment or water treatment to maintain existing water quality. Several other known contaminants have the potential to affect the quality of groundwater for domestic use in the Manteca area(UWMP 2000). The concentrations of these have remained relatively stable,but have the potential to increase as a result of groundwater movement. They are: Nitrate Elevated levels of nitrate(as NOO are found at six city wells at 30 milligrams per liter(mg/1) or higher. If these levels were to increase above the MCL of 45 mg/1,production would have to stop from the source well and modified with screening of the upper portion of the aquifer where higher concentrations are found, or treating the water. The source of the nitrate is believed to be from past agricultural activities in the area. EDAW DER Hydrology and Water Quality 4.9-6 City of Manteca