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Background <br /> According to EVAX(1992) and Remediation Risk Management (1993), five underground <br /> storage tanks were removed (one 8,000-gallon gasoline, one 7,500-gallon premium <br /> gasoline, two 4,000-gallon for unleaded gasoline, and one waste oil tank were reportedly <br /> removed). Thirteen soil samples were reportedly collected and chemically analyzed at <br /> FGL Environmental of Stockton, California. Those samples indicated petroleum <br /> hydrocarbon leakage in the immediate tank pit vicinity. In addition, EVAX also performed <br /> a soil vapor survey, the results of which were used to locate the initial three-groundwater <br /> monitoring wells. <br /> Wright had performed an additional subsurface sampling assessment and installed six <br /> monitoring wells, and has conducted quarterly groundwater monitoring. Wright had <br /> pursued a possible site closure approach based upon that data. However, upon review of <br /> PHS-EHD and RWQCB, closure was not approved due to elevated TPHG and Benzene <br /> levels at MW-9 and MW-3 (See Figures 1, 2 and Reference). <br /> Previous site assessment activities have mapped the dissolved plume; the former <br /> underground tank sources have been removed and quarterly monitoring sampling with <br /> reports are ongoing at the site_ Additional subsurface assessment was completed in 2000 <br /> and 2001 to address locally elevated residual contaminants on-site, specifically in the <br /> immediate vicinities of Wells MW-3 and MW-9, Field modifications to the work were <br /> made in consultation with the PHS-EHD representative as discussed below. <br /> Additional subsurface study was requested in a letter dated November 29, 1999 from the <br /> San Joaquin Public Health Services Environmental Health Division (PHS-EHD) for <br /> additional site assessment. This work was performed to address locally elevated residual <br /> contaminants on-site, and a suspect additional contaminant source, specifically in the <br /> immediate vicinities of wells MW-3 and MW-9. The first phase of work was performed in <br /> April 2000 to attempt to delineate selected areas. Following a review of that data, Wright <br /> and PHS-EHD agreed to review all the site data and to perform additional studies to <br /> ascertain whether a possible tank source was present. This report presents the subsurface <br /> data from the April, 2000 and April, 2001 investigations that in our opinion have defined <br /> the plume. <br /> This information together with the quarterly monitoring data and soil samples collected for <br /> assessing site biologic activity are presented for this corrective action report. Three <br /> options are presented for site cleanup, which in our opinion can address site cleanup for <br /> cleanup of the elevated TPHG and Benzene concentrations of concern to the agencies in a <br /> cost-effective manner. <br /> r..r <br /> Page 3 <br />