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%. „retial Study—LID Annexation relation to the path of the San Joaquin River suggests that the site was previously the outfall location of the San Joaquin River into a delta environment of braided streams and marshlands. Sediments underlying the site documented in earlier studies consist of unconsolidated and discontinuous layers and lenses of silt, sand,clay,and gravel.The subsurface of the site is highly variable in both thickness and distribution of deposits. The project site soils are alluvial (deposited by water) in origin and were placed over approximately the last one million years(Late Quaternary)during episodes of deposition followed by periods of nondeposition and erosion.The site soils,as mapped by the U.S. Soil Conservation Service are of the following soil types: 133 -Columbia fine sandy loam,clayey substratum, partially drained; 153 -Egbert silty clay loam,partially drained; and 197—Merritt silty clay loam, partially drained.These soil units are similar in nature and generally are silty clays to silty sands. Detailed USDA Soil Survey Soil descriptions are presented in the Baseline Geotechnical Assessment for the River Islands Project, prepared by ENGEO Geotechnical Engineers for the River Islands EIR. Site observations indicated that the actual surface soils observed at the site were mapped in previous geotechnical investigations as silty sands,clayey to sandy silts, and two areas of moderately to highly plastic clays. The descriptions of the underlying soils are similar,consisting of silty sands,poorly to well- graded sands,clayey to sandy silts,and moderately to highly plastic clays. In general,the site soils appear sandier in the eastern portion of the site,with localized clayey pockets. The central portion of the site is generally silty with lesser amounts of clay and sand and localized clayey zones. The western portion is generally sandy with localized clays and silts. Seismic hazards include earthquake-induced ground shaking or rupture,subsidence, liquefaction,and tsunamis or seiches. Strong earthquakes generated along a fault system create ground shaking,which attenuates with distance from the epicenter.The area affected by strong ground shaking would depend on the characteristics of the earthquake, such as intensity and duration and the location of the epicenter. No active faults are mapped across the project site by the California Geological Survey(CGS)or the United States Geological Survey(USGS). The nearest known surface trace of a fault designated as active by the CGS is the Greenville fault, located approximately 20 miles west of the project site.The next significant fault zone designated active by the CGS is the Calaveras fault, located approximately 30 miles west of the site.The closest trace of the San Andreas Fault is located approximately 55 miles to the west of the site. With the previous LAFCo Initial Study/MND Mitigation Monitoring Program,a fault and hazard mitigation measure was adopted for all new facilities constructed for electrical service. This mitigation shall remain in full force and effect and be incorporated into the proposed Mitigation Monitoring and Reporting Program(MMRP)for this negative declaration. 2.6.1 Regulatory Background The Hazard Management Element of the Lathrop General Plan outlines goals and policies associated with earth/soils issues. The following policies relate to the proposed project: All new building construction shall conform to the latest seismic requirements of the Uniform Building Code as a minimum standard. If the preliminary geologic report indicates the presence of critically expansive soils or other soil problems(e.g.,potential for liquefaction which if not corrected could lead to structural defects),the developer shall provide such additional soils investigation for each 36