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Mr Harlin KnollN <br /> San Joaquin County Environmental Health Division <br /> 20 February 2001 <br /> Page 6 <br /> Rationale for Site Closure <br /> IBridgestone/Firestone is requesting site closure based on the following factors <br /> ❑ Future and/or ongoing sources of gasoline and its constituents, specifically <br /> MTBE, including USTs, related piping, and impacted soil in the vicinity of <br /> the USTs have been removed or properly closed in place at the site The in- <br /> place USTs have been closed since 1967 and never contained MTBE as a <br /> fuel component The other onsite USTs were non-operational when <br /> removed in 1990 and also did not contain fuel with the MTBE additive <br /> I ❑ Analytical data collected during well installation activities indicate <br /> concentrations of TPHg, BTEX, and MTBE in the site soils that would fall into <br /> California's category of low risk Three wells were drilled and selected soil <br /> samples from each boring were collected and analyzed TPHg, BTEX, and <br /> MTBE were not detected in soil samples from wells MW-2 and MW-3 The <br /> soil sample analyzed from MW-1 yielded MTBE at a concentration of <br /> 99 µg/kg and nondetectable concentrations of TPHg and BTEX These <br /> . concentrations are below recently published PRGs <br /> ❑ Groundwater samples collected during the four rounds of groundwater <br /> sampling indicate low impact to groundwater at the site The cross-gradient <br /> well MW-3 did not contain detectable concentrations of constituents <br /> associated with gasoline In monitoring well MW-1, TPHg and BTEX were <br /> not detected and only small concentrations of MTBE were detected during <br /> four quarterly rounds of sampling (42 0, 7 7, 7 9, and 4 0 µg/I of MTBE, <br /> respectively) Well MW-2 had no detectable concentrations of MTBE The <br /> MTBE detected did not originate from the site operations and USTs These <br /> groundwater concentrations are below California Water Resources Control <br /> Board guidelines for low risk sites <br /> ❑ Total mass calculations indicate that approximately 1/4 pound of total <br /> petroleum hydrocarbons remain on site <br /> ❑ Accordingto the California Water Service there are no groundwater <br /> drinking wells within 2,000 feet of the site <br /> ❑ The site is paved with asphalt, reducing the likelihood of surface water <br /> infiltration and the potential for migration of the detected constituents in the <br /> . soil to groundwater <br /> S\BFS\STOCKTON\LTR\LTR007 DOC 2/20/01 <br />