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06 October 2006 AGE-NC Project No. 04-1207 Page 2 of 9 Riverbank, and Turlock Lake Formations and overlying Recent alluvium are the principal sources of domestic ground water in the 13,500-square mile San Joaquin Valley Ground Water Basin (Basin 5-22). Based on the United States Department of Agriculture-Natural Resources Conservation Service's Web Soil Survey map, surface sediment at the site area is classified as Tokay-Urban land complex soil. The Tokay series, found on low fan terraces, consists of very deep,well-drained soils formed in alluvium derived mainly from granitic rock sources. The sedimentary units at the site are relatively horizontal and continuous.Based on quarterly ground water monitoring events conducted at the site beginning in April 2005, ground water is currently encountered at approximately 47 feet to 50 feet below surface grade (bsg) and flows toward the southwest. The uppermost ground water flows in an unconfined aquifer; first ground water occurs in a silty sand or sandy silt layer,coarsening to fine-to coarse-grained sand at approximately 60 feet bsg. Ground water is considered to be of beneficial use and is used for domestic, industrial and commercial purposes. 2.2. UNDERGROUND STORAGE TANK REMOVAL Based on conversations conducted by J.H. Kleinfelder& Associates (JHK) with former property owner Tom Tucker and San Joaquin County Environmental Health Department(EHD)personnel, two 1,000-gallon USTs were removed from the site in 1984 or 1985. No further information regarding the excavation and removal of the USTs is available to AGE at this time. 2.3. PREVIOUS SITE ASSESSMENT ACTIVITIES • On 16 October 1985, JHK advanced one soil boring to a depth of 65 feet bsg for the installation of one ground water monitoring well (MW-1; Figure 2). Soil samples taken at 35 feet(B 1-35)and 40 feet bsg(B 1-40)contained benzene,toluene,ethylbenzene,and total xylenes(BTEX)at concentrations as high as 27 milligrams per kilogram(mg/kg; xylenes). Total petroleum hydrocarbons quantified as gasoline(TPH-g)were detected at a maximum concentration of 193 mg/kg. • On 19 October 1985,monitoring well MW-1 was developed and ground water samples were collected for analysis.BTEX compounds were detected at concentrations of 21.2 micrograms per liter (µg/1) benzene, 204 µg/1 toluene, 12.4 µg/l ethylbenzene, and 1,440 µg/1 total xylenes. TPH-g was detected at a concentration of 16,000 µg/1;total lead was detected at a concentration of 110 µg/l. Advanced GeoEnvironmental,Inc.