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, <br /> GEOMATRIX <br /> Mr. Robert Mihalovich <br /> Chevron Environmental Management Company <br /> May 9, 2002 <br /> Page 2 <br /> 2. HERD advises Site Mitigation Staff to assure that metals,particularly lead, are not also <br /> present at the site since a gasoline station was formerly at the site and BTEX has been <br /> detected in groundwater. <br /> The objective of the additional investigations performed in May and October 2000 was to <br /> assess the lateral extent of petroleum in soil at off-site locations and to evaluate <br /> groundwater quality on site and downgradient of the site. The investigation focused on <br /> evaluating the potential impacts associated with the residual heavy petroleum <br /> hydrocarbon, specifically crude and/or fuel oil, from ChevronTexaco's former Old Valley <br /> Pipeline (OVP) located along the northern boundary of the site adjacent to the railroad <br /> right-of-way. Lead is not a component of the historic crude and fuel oil. <br /> 3. Additional soil and groundwater samples were collected, analyzed for total petroleum <br /> hydrocarbons(TPH),PAHs, and BTEX. The additional data revealed BTEX in <br /> groundwater. <br /> Five groundwater grab samples were collected as part of the investigation and analyzed <br /> for TPH quantified as gasoline and diesel (TPHg and TPHd); benzene, toluene, <br /> ethylbenzene, and xylenes (BTEX); and polynuclear aromatic hydrocarbons (PAHs). <br /> Toluene, ethylbenzene, and xylenes were detected at concentrations less than 2.6 µg/l. <br /> Benzene was detected in only one of five grab groundwater samples at a concentration of <br /> 0.6 micrograms per liter(µg/1), which is slightly above the laboratory reporting limit of <br /> 0.5 µg/1. BTEX compounds were not detected above the laboratory reporting limits in <br /> previous grab groundwater samples. <br /> SPECIFIC COMMENTS <br /> 1. Previously,HERD commented that the vertical extent of soil contamination required <br /> clarification (DTSC, 2000). The vertical extent of soil sampling was not addressed in <br /> the additional data collected. Soil sampling for the combined data set was limited to 8.5 <br /> to 15 ft below ground surface(bgs). <br /> As indicated above, Geomatrix provided a response to HERD's initial comment in a <br /> March 29, 2000 letter, a copy of which was attached in Appendix A of the December <br /> 2000 Report of Additional Soil and Groundwater Investigation,prepared by Geomatrix. <br /> As part of the overall technical approach for OVP sites, borings with petroleum <br /> hydrocarbon-affected soil are advanced until affected soil is no longer observed in the <br /> recovered soil core. As a conservative estimate, soil samples submitted for chemical <br /> analysis are generally from the interval of the core with the most visibly affected soil. <br /> Thus, available analytical results for a particular soil boring do not necessarily reflect the <br /> vertical extent of observed petroleum at a site,but rather the depth of the most visually <br /> impacted depth interval. <br />