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- <br /> w - <br /> R <br /> t� <br /> r , <br /> 1 { . <br /> t <br /> EXECUTIVE SUMMARY <br /> t <br /> This report has been prepared by Pacific Environmental Group, Inc. (P:�CIFIC) 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 3 <br /> I investigative findings is presented below: <br /> o A partially buried 5,000-gallon transmission fluid storage tank was S <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 /> k;l <br /> excavation. <br /> 1 <br /> e The San Joaquin County Public Health Services Department issued an 71 <br /> "Unauthorized Storage Tank Release/Contamination Site Report"on <br /> z January 30, 1990, and requested additional investigation. . <br /> f o PACIFIC installed Groundwater!Monitoring Wells U-1 through U-3 <br /> on Octob-er 24 and 25, 1690. Three additional groundwater monitoring <br /> wells designated U-4 through U-6,and three exploratory soil borings, z <br /> h U-A through U-C,were installed on site on May 9, 1991. <br /> o The site is underlain primarily by silts and clays to the rpm-dmum depth <br /> explored of 27 feet. Sur-ficial sands were observed in the northwestern <br /> and southeastern portions of the site,at an approximate thickness of 5 <br /> to 8 feet. Significant subsurface sands were observed at approximate <br /> depths of 6 feet in U-6, S-1/2 feet in U-B, 16-1/2 feet in U-C,and ' <br /> 20 feet in U-4. These sands range from approximately 1 foot to 5 feet <br /> in thickness,but appear not to be laterally continuous across the site. <br /> o Hy 4xocarbon concentrations in soil samples collected during October <br /> 1990 and May 1991 ranged from none-detected to 1,800 parts per <br /> million(ppm)TPH-gasoline,and from none-detected to 4,900 ppm <br /> TPH-diesel. Hvdroearbon concentrations were at a maximum at <br /> depths between 5 and 8_i/2 feet,-with_th..e_maximum TPH.-gasoline <br /> concentration occt:rrin;tn U-1,and the maximum TPH-diesel — — ----- -- — - <br /> , 6 <br /> .3100101/REFORT- i September 30, 1991 <br />