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,16 i <br /> 4 SITE INVESTIGATION SUMMARY <br /> Based on previous and current Site investigation results PSC resents the following <br /> p g P g <br /> summary of findings <br /> • A 1,000-gallon gasoline UST was removed from the Site in December 1990 <br /> • The Site is located in a mix of commercial and residential properties <br /> • The closest residential property to the former UST is about 150 feet away <br /> • The closest surface water body is about 4,500 feet away <br /> • An operating gasoline station, the subject of an existing County leaking UST, is <br /> located about 1 block away <br /> • Research information Indicates that the 1725 El Dorado Street property, across the <br /> street from the Site, was historically operated as a retail gasoline station <br /> • Three phases of site investigation have been performed in April 1998, in July <br /> 1999, and in March 2002 Eight Geoprobe borings have been driven, 4 <br /> groundwater monitoring wells have been completed, and an air sparging well and <br /> a soil vapor extraction well have been installed <br /> • Groundwater monitoring has been performed in 2000 and 2001 <br /> O Subsurface soils in the vicinity of the Site are primarily comprised of silt and clay <br /> to at least 50 feet <br /> o Initial groundwater, situated in the clayey matrix, was typically observed at a <br /> depth of 30 to 35 feet Groundwater is slow to yield, but typically rises under <br /> confined pressure to about 23 to 25 feet <br /> • Groundwater flows east-southeast at a gradient of about 0 0026 ft/ft <br /> • BTEX concentrations in soil samples collected above the groundwater table are <br /> relatively low compared to those obtained below Higher BTEX concentrations in <br /> soil samples collected below the groundwater table may be a result of the <br /> contaminated groundwater present within their matrix <br /> • TPHg concentrations in soil samples collected above the groundwater table are <br /> relatively higher compared to those obtained below BTEX concentrations, once <br /> potentially present in these higher TPHg-impacted soil samples, appear to have <br /> degraded <br /> • The lateral extent of petroleum impacted soil appears to be narrowly confined in <br /> the vicinity of the former UST The vertical extent of impact is evaluated to be 50 <br /> to 55 feet <br /> OR Oxygenate compounds have not been detected in any soil sample <br /> 14 <br /> March 2002 <br /> Subsurface Site Investigation <br /> 1717 South Center Street-Stockton,California <br /> Prepared by Philip Services Corp <br /> H 5ENV1624001321121382EG\PmjeculStockCentlmarch20P2mvestigauon doc May 14,2002 <br />