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Site Assessment Report,Site Conceptual Model,and Site Investigation Work Plan R& L Diesel Services,2417 West Lane, Stockton, California, 95205 Tertiary deposits incorporate the Pliocene-recent flood basin deposits, the Pliocene-Pleistocene Laguna Formation and the Miocene Pliocene Mehrten Formation. The Pliocene-recent flood basin deposits are exposed in the delta area of the Sang Joaquin Valley. They are essentially fine-grained transported versions of the Laguna, Riverbank, and Modesto Formations and recent deposits. This unit's thickness ranges from 0 to 11,400 feet and has low permability. The 1 ' Pliocene-Pleistocene Laguna Formation consists of discontinuous stream-laid sand and silt with -" minor amounts of clay and gravel. The thickness ranges from 400-1000 feet, and permeability ranges from moderate-high. The Miocene-Pliocene Mehrten Formation is composed of moderately-well indurated andesitic sand and sandstone with conglomerate interbeds. The F thickness ranges from 400-600 feet in the Stockton area. Site-specific geology is unavailable as logging lithologylduring drilling activities was not conducted during the March 2008 sampling event. However, there are two.open sites nearby - (American Forest Products approximately 0.2 miles north on the west side of West Lane and Pacific Pride approximately 0.5 miles north on the east side of West Lane)with available public P, groundwater and/or lithologic data. Advanced GeoEnviromental, Inc., the environmental consulting company working on the Pacific Pride site, has installed five monitoring wells while logging borehole lithology. Collaboratively summarizing the five logs reveals a profile of clayey silt to 5 feet bgs, sandy silt to 10 feet bgs, silty sand to 20 feet bgs, clayey sandy silt and silty sand to 55 feet bgs, sand to 65 feet bgs and sandy silt t680 feet bgs. Drilling at the R&L site has encountered a tight, hard clay layer at approximately 40 feet below grade which caused refusal for the geoprobe being used to advance the boriings. 2.2.2 Hydroaeolocly The eastern San Joaquin Valley is the southernmost section of the Great Valley Geomorphic f Province, a broad basin bordered by the Sierra Nevada on the east and Coast Range Complex to the west. The San Joaquin Subbasin is composed of unconsolidated and serhiconsolidated sedimentary deposits, bordered by the Modesto, Delta-Mendota, and Tracy Subbasins to the 4 , south, southwest and west, respectively. The San Joaquin Subbasin is drained by the San Joaquin River and its tributaries northward and discharges into the San Francisco Bay. Annual precipitation ranges from 11 inches in the southwest to 25 inches in the northeast. y The aquifer system consists of the late Tertiary to Quaternary-aged continental deposits detailed previously in the Geology section, with the upper Quaternary deposits being moderately Fto highly permeable and the lower Tertiary deposits ranging in permeability from low to high. No site-specific groundwater gradient data is available however, there are two open sites Fsnearby (American Forest Products approximately 0.2 miles north on the west side of West Lane and Pacific Pride approximately 0.5 miles north on the east side of West Lane) with available public groundwater and/or lithologic data. Advanced GeoEviromental, Inc., the environmental consulting company working on the Pacific Pride site, has installed five monitoring wells (MW-1 MW, -5). According to their first quarter 2008 monitoring report, depth to water ranged from 43.36 feet bgs to 47.25 feet bgs and F] groundwater elevation ranged from 29.20 to 29.44 feet below mean sea level (MSL). The t groundwater gradient was southwest at 0.003 feet/foot. I URS, the environmental consulting company working on the American Forest Products site, have installed nine monitoring wells 'A (DMW-I-DMW-9). According to their third quarter 2007 imonitoring report, depth to water ranged from 44 to 45 feet bgs and the groundwater elevation was approximately 27 feet below MSL. The groundwater gradient was northeast at 0.003 feetlfoot. F1, F1