ARCHIVED REPORTS_XR0003895 - Laserfiche WebLink

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PURPOSE AND SCOPE On November 28, 1994, Ms. Pam Lopez's consultant, RAH Environmental, Inc. , drilled and sampled a soil boring (SBA) in order to determine if hydrocarbon contamination from the former tank had impacted ground water. The soil boring was drilled in conjunction with seven soil borings drilled by RAH Environmental for Tri-Valley Growers (TVG) . SITE LOCATION AND DESCRIPTION The site is a private residence located at 25500 Nowell Road, Thornton, California. It is 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) . 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 9, 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 (TVG well logs and quarterly monitor reports) . It was noted in the log of MW4 , that visible product had been present at the top of this aquifer. During the majority 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 SITEJ ��"'� One, 500 gallon, underground, gasoline storage tank was removed from the site, on October 9 , 1989. No BTEX compounds were found zn the soil sample, taken during the tank pull, but 3 . 9 mg/kg TPHg compounds were detected in the sample. 1