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1 GECMATRIX <br /> SOIL AND GROUNDWATER INVESTIGATION REPORT <br /> ,} 35275 Welty Road — APN 255-180-09 <br /> Vernalis, California <br /> EXECUTIVE SUMMARY <br /> This report presents results of field activities conducted in June and November 1999 at the <br /> 35275 Welty Road site (San Joaquin County Assessor's Parcel Number 255-180-09) in <br /> Vernalis, California (the site; Figure 1). Field activities included the advancement of seven soil <br /> borings for the collection of soil and groundwater samples and sampling of one off-site ground- <br /> water monitoring well. This work was performed in accordance with Geomatrix's June 12, <br /> 1999 work plan submitted to the California Regional Water Quality Control Board, Central <br /> Valley Region (RWQCB). The purpose of the investigation was to assess the vertical and <br /> lateral extent of soil affected by weathered Old Valley Pipeline(OVP) crude oil and to assess <br /> whether residual OVP oil present in the site subsurface provides a source of dissolved <br /> petroleum constituents to groundwater. Trichloroethene (TCE) has historically been detected <br /> in shallow soil in one area of the site but not in shallow groundwater. At the request of the <br /> RWQCB,this investigation also evaluated the presence of TCE in site soil at depths below <br /> previous soil samples. <br /> Depth to groundwater was approximately 30 to 32 feet below ground surface (bg's) with a <br /> gradient direction to the northeast; these data are consistent with previous measurements by <br /> others. Stained soil and hydrocarbon odor were observed in three borings from depths of 15.5 <br /> to 51.5 feet bgs. No TCE or other nonpetroleum volatile organic compounds were detected in <br /> the soil samples collected from boring GMX-1. <br /> No petroleum hydrocarbons were detected in a groundwater sample collected from a previously <br /> installed off-site monitoring well located downgradient of on-site petroleum hydrocarbon <br /> affected soil. Petroleum hydrocarbons were detected in a grab groundwater sample collected <br /> from a second location downgradient of the site. Although this location is also downgradient <br /> from an on-site monitoring well that contains a sheen of petroleum, the detected constituents in <br /> the grab sample are uncharacteristic of OVP sites, and the chromatograms are dissimilar to <br /> L%DOC_SAFF\5000S153801S01LGW RPT.DOC ES-1 <br />