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N <br /> i' <br /> a: EXECUTIVE SUMMARY <br /> This report has been prepared by Pacific Environmental Group Inc. (PACIFIC) to <br /> document the findings of a soil and groundwater investigation performed at UNOCAL <br /> Bulk Plant 0788 located at 8203 East 11th Street in Tracy, California. A.summary of <br /> the investigative findings is presented below: <br /> o A partially buried 5,000-gallon transmission fluid storage tank was <br /> }' removed from the southeastern portion of the site on <br /> December 13, 1989. Analytical results indicated that low levels of <br /> petroleum hydrocarbons remained in the soils adjacent to the <br /> excavation. <br /> o The San Joaquin County Public Health Services Department issued an <br /> "Unauthorized Storage Tank Release/Contamination Site Report" on <br /> r January 30, 1990, and requested additional investigation. el <br /> : a <br /> o PACIFIC installed groundwater Monitoring Wells U-1 through U-3 on <br /> October 24 and 25, 1990. Three groundwater monitoring wells <br /> designated U-4 through U-6, and three exploratory foil borings, <br /> designated U-A through U-C, were installed on site on May 9, 1991. <br /> r Four additional groundwater monitoring wells designated )-7 through <br /> l.t U-10 were installed on March 10 through March 12, 1992. !i <br /> o The site is underlain primarily by silts, clays, and silty sands to the <br /> maximum depth explored of 16-1/2 feet. The clays and silts were <br /> found at depths from grade to 16 feet. Silty sands were `observed at <br /> depths below 15-1/2 feet to 16-1/2 feet the maximum depth explored. <br /> ry r� Silty sands were encountered at shallower depth intervals in previous <br /> ; phases of investigation. High-permeability sediments occur below the <br /> L1 above-ground storage tanks and may be providing { route for <br /> hydrocarbon migration. <br /> o Hydrocarbon concentrations in soil samples collected Iduring the <br /> March 10 through March 12, 1992, investigation ranged from 2.0 parts <br /> per million (ppm) to 7.8 ppm total petroleum hydrocarbons calculated <br /> 3100103/REPORTS i i June 11, 1992 <br />