ARCHIVED REPORTS_DRAFT ENVIRONMENTAL IMPACT REPORT

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outfall pipelines are also located in the 500-year floodplain. No project components would be located in the 100- year floodplain(City of Manteca 2003a). Table 4.9-1 Sources and Percent Contributions of Flow and TDS in the San Joaquin River at Vernalis (1985-1994) Source Discharge' Percent TDS Loadz(Tons x Percent (Acre-Feet x 1000) Contribution 1000) Contribution Eastside Tributaries 1,323 70 148 16 Groundwater 90 5 191 20 Westside Tributaries 68 4 201 21 Grassland Wetlands 60 3 74 8 Groundwater Inflow 11 1 77 8 Westside Surface Returns 70 4 57 6 Subsurface Return Flows 11 1 25 3 (Main Stem San Joaquin River) Surface Return Flows 250 13 150 16 (Main Stem San Joaquin River) Municipal and Industrial 15 1 14 2 Total 1,899 100 938 100 Notes: TDS=total dissolved solids ' 10-year mean annual flow calculated from 1985-1994. 2 10-year mean annual load calculated from 1985-1994. Source:Quinn and Tulloch 2002 The WQCF site and proposed pipeline alignments are located in an inundation area for three dams located within the Manteca vicinity. The project site could be subject to flooding if the Tulloch Dam(located 36 miles east), San Luis Dam(located 46 miles south), or New Melones Dam(located 41 miles east) failed(City of Manteca 1988). The California Government Code (Section 8589.5)requires local jurisdictions to adopt emergency evacuation procedures for populated inundation areas. The local Office of Emergency Services prepared a Dam Failure Plan that includes a description of dams, direction of floodwaters,responsibilities of local jurisdictions, and evacuation plans(City of Manteca 2003a). Because an adequate evacuation plan exists in case of a dam failure that could affect the project site, flooding issues related to dam failure are not discussed further in this EIR. The WQCF site and proposed pipeline alignments are not located near an open body of water and therefore would not be subject to adverse effects associated with a seich;this issue is therefore not addressed further in this EIR. The effluent outfall pipeline and outfall structure would not be affected by a seich because the outfall pipeline and associated structure would be constructed underground. The project area is not located near the ocean and therefore would not be subject to adverse effects associated with a tsunami;this issue is therefore not addressed further in this EIR. Storm water drainage is provide in the city by a system of gravity storm drain lines that terminate at detention or retention facilities to provide storage to attenuate peak flows. There are currently 32 detention basins located in the city with up to 65 additional detention basins planned for the future(City of Manteca 2006). Most stormwater is pumped into the South San Joaquin Irrigation District(SSJID)drains. There are currently 38 drainage pump stations in the city with an additional pump station planned for each proposed detention basin. SSJID operates drainage facilities that traverse the City of Manteca and carry a portion of the City's stormwater drainage. Water EDAW DER Hydrology and Water Quality 4.9-4 City of Manteca