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r PURPOSE AND SCOPE In response to San Joaquin County, Environmental Health' s letter of June 10 , 1994 , Tri-Valley Growers and their consultant RAH Environmental, Inc. drilled and sampled seven soil borings, on November 28 , 1994 , in order to further define extent of the soil and ground water contamination at the Thornton Plant T site. SITE LOCATION AND DESCRIPTION Tri-Valley Growers Plant T is located at 26200 Nowell Road, Thornton, California. The site as located in projected Section 3 , T4N, R5E, of the MDB&M at an elevation of approximately 11 feet above mean sea level (see Figures 1 and 2) . This Tri-Valley site is an operating cannery. GEOLOGY AND HYDROGEOLOGY The site is located on recent flood plain and channel deposits derived from the Mokelumne River. See Exceltech, Inc report of November 91 1987 for further discussion of geology and for well reconnaissance. In the area of interest the soils are made up of unconsolidated clayey silts, silty clay, sandy clays, clay sands and silty sands. Of most importance, at this site, is the silty sand aquifer between 14 and 19 feet below the surface. It was noted in the log of MW4, that visible product had been present at the top of this aquifer. During the ma]oraty of the time when the site had been monitored, the top of this sand had been below the top of ground water. This indicates that the aquifer is confined. During those time periods that the ground water had fallen below the top of the sand in MW4, as a result of pumping, the reported hydrocarbon concentration levels have increased. PREVIOUS WORK AT THE SITE Two gasoline underground storage tanks were removed from the area of interest during January and February 1987 . Appreciable amounts of hydrocarbon contamination were found in the soil samples taken during the tank pull. After the tank pull, four ground water monitor wells were installed by Exceltech. Two additional monitor wells were later installed by Water Work. Of these wells, only MW4 has ever shown a significant amount of hydrocarbon contamination. The other wells provide an outer limit to the hydrocarbon contamination on the site. A ground water recovery system was placed into operation on May 13 , 1991. The system was set to pump water from MW4 .