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2 November 21, 2011 Cardno ERI 2789C.R02 Former Mobil Service Station 99CAS, Stockton, California The subject site is made up of two separate parcels of land. The parcel on the western portion of the site (assessor's parcel number 115-140-06) is currently owned by Mr. Arthur Lavagnino. The parcel on the eastern portion of the site (assessor's parcel number 115-140-07) is currently owned by Mr. Duane Berndt and Ms. Wendy Berndt of the Guido G. Segarini Trust. Mobil Oil Corporation leased the property from 1955 to 1985 (ETIC, 2010). The surrounding land use is primarily residential with some commercial buildings, church complexes, and elementary schools nearby. Parking lots are located immediately north of the site, and a residential house borders the site to the west. GEOLOGY AND HYDROGEOLOGY The site is located in the Great Valley geomorphic province and the Eastern San Joaquin Subbasin of the San Joaquin Valley Groundwater Basin. The Great Valley geomorphic province is bounded by the Coast Ranges to the west and the Sierra Nevada province to the east. The Eastern San Joaquin Subbasin is defined by the areal extent of unconsolidated to semi -consolidated sedimentary deposits bounded by the Mokelumne River to the north and northwest, the San Joaquin River to the west, the Stanislaus River to the south, and consolidated bedrock to the east. Water -bearing formations in the Eastern San Joaquin Subbasin include alluvium, the Modesto/Riverbank Formations, the Flood Basin Deposits, the Laguna Formation, and the Mehrten Formation. The Calaveras River, the nearest surface water body, is located approximately 3,200 feet northwest of the site (ETIC, 2011). Yosemite Lake and the Smith Canal are located approximately 4,860 feet southwest of the site. In the eastern part of the Basin, the predominant anion is bicarbonate. The majority of groundwater throughout the Basin is characterized by calcium -magnesium bicarbonate or calcium -sodium bicarbonate types. Areas of chloride -type water are present along the western margin of the subbasin along the San Joaquin River. Degraded water has been moving east along a 16 -mile front on the eastern side of the Delta as a result of declining groundwater levels. This has been evident in the Stockton area where the saline front has been moving eastward at a rate of approximately 140 to 150 feet per year (ETIC, 2011). During previous site investigations, clayey silt and silty clay with lenses of poorly graded sand and clayey sand have been observed to 107 feet bgs, the maximum depth explored (ETIC, 2011). The DTW at the site has historically ranged from 32 to 41 feet bgs. During the third quarter 2011 groundwater monitoring and sampling event, the groundwater flow direction in the shallow and deep zones was towards the east and northeast, respectively (Cardno ERI, 2011 b). PREVIOUS WORK Soil and groundwater investigations have been conducted at the site since 1994. Previous work has included the drilling of soil borings, installation of wells, removal of USTs, and groundwater monitoring and sampling