ARCHIVED REPORTS_XR0003896 - Laserfiche WebLink

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PURPOSE AND SCOPE Ms. Pam Lopez and her consultant RAH Environmental, Inc. (RAH) , propose to drill a soil boring in order to determine if hydrocarbon contamination from the former tank has impacted ground water. SITE LOCATION AND DESCRIPTION The site is a private residence located at 26500 Nowell Road, Thornton, California The site is located in projected Section 3 , T4N, R5E, of 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. 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 at between 14 and 19 feet below the surface, (Tri-Valley Growers well logs and quarterly monitoring reports) . It was noted in the log of MW 4 , that visible product had been present at the top of this aquifer. During the majority of the time that the Tri-Valley site has been monitored the top of this sand has been below the top of ground water, indicating that the aquifer is confined. During those time periods that the ground water has fallen below the top of the sand in MW4 , as a result of pumping, the reported hydrocarbon concentration levels had increased. PREVIOUS WORK AT THE SITE One, 1000 gallon, gasoline underground storage tank was removed from the site, on October 9 , 1989 . No BTEX compounds were found in the soil sample taken during the tank pull, but 3 . 9 mg/kg TPH-G compounds were detected in the sample. SOIL BORING Selection of Soil Boring Location Because of the possibility of cross contamination resulting from the neighboring Tri-Valley Growers plume, the soil boring will be drilled on the location of the former tank. . 1