ARCHIVED REPORTS XR0009987 - Laserfiche WebLink

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