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Versar - McLaren/Hart erosional activities occurring in the Sierra Nevada Mountain Range during the Pleistocene period The results of this erosion are mixed alluvial deposits which are covered by silt, sand, clay, gravel, and some channel deposits of the San Joaquin River drainage area during the Quartenary period (Norris and Webb, 1990) Stockton is located in a relatively low risk seismic area of faulting The Stockton Fault is the closest fault to the Site, and is located south of the City of Stockton The closest surface water body is the Stockton Channel, located east of the Site, across North Center Street According to reports completed by Shell as part of the on-site subsurface UST investigation, the groundwater flow direction beneath the Site is to the northeast, away from the Stockton Channel, and is expected to occur at shallow depths (within approximately 10 to 20 feet below ground surface) Versar-McLaren/Hart reviewed information contained in the U S Department of Agriculture's (USDA) Soil Survey of San Joaquin County, California The detailed soil classification beneath the Site is identified as "urban soils" These soils are associated with areas approximately 80 to 85% covered by roads, driveways, parking lots, houses, and other structures The soil under these structures has been graded and mixed or has been covered with fill material The texture of the surface layer is highly variable Urban land soils are deep to moderately deep, nearly level and gently sloping, poorly-drained to well-drained soils, and are located on alluvial fans, flood plains, and coastal terraces Slope ranges from 0 to 5 percent (USDA, SCS, 1980) The general soil classification beneath the Site is Jacktone-Hollenbeck-Stockton (JHS) soil The JHS soil is found on basin rims or in basins and is characterized as a somewhat poorly-drained to moderately well-drained, fine-textured soil The soil is moderately deep to deep with a cemented hardpan 24 Historical Land Use Aerial Photograph Review Versar-McLaren/Hart reviewed available historical aerial photographs of the Sites and surrounding properties for the years 1937, 1952, 1963 and 1984 at the San Joaquin County Surveyor's Office in Stockton, California A summary of the historical aerial photograph review is presented below -4-