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Mr Harlin Knoll <br /> m ntal Health Division (DR1 (3N <br /> San Joaquin County Environme <br />' 24 October 2000 <br /> Page 7 <br /> Following written acceptance of site closure, BFS will close the monitoring wells and <br /> restore the surfaces around the well boxes to their previous condition <br /> Rationale for Site Closure <br />' The EPA's Drinking Water Advisory Consumer Acceptability Advice and Health Effects <br /> Analysis on MTBE (EPA-822-F-97-009 December 1997), states about MTBE "that <br /> keeping concentrations in the range of 20 to 40 micrograms per liter (µg/I) of water or <br />' below will likely avert unpleasant taste and odor effects " Additionally, the State of <br /> California has proposed primary drinking water standards as a public health goal for <br />' MTBE of 13 µg/1 Although these values are proposed as goals and considered low by <br /> the industry, the concentrations of MTBE found in the shallow, unused groundwater at <br /> the site are below these aggressive objectives <br />' Bridgestone/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 <br /> ❑ 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 proposed goals or published Regional Water <br />' Quality Control Board objectives <br /> ❑ Groundwater samples collected during the three rounds of groundwater <br />' sampling indicate the following low impact to groundwater at the site The <br /> cross-gradient well MW-3 did not contain detectable concentrations of <br /> constituents associated with gasoline In monitoring well MW-1, TPHg and <br />' BTEX were not detected, and only small concentrations of MTBE were <br /> detected during three quarterly rounds of sampling (7 7, 7 9, and 4 0 µg/I of <br />' MTBE, respectively) Well MW-2 had no detectable concentrations of <br /> MTBE These groundwater concentrations are below EPA and California <br />' proposed goals <br />' S\13FS\STOCKTON\LTR\LTR005 DOC 10/24/00 <br />