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Mr. Harlin Knoll C) RIIN <br /> San Joaquin County Environmental Health Division <br /> 27 June 2001 <br /> *40, Page 5 <br /> L ❑ Analytical data collected during well installation activities indicate <br /> concentrations of TPHg, BTEX, and MTBE in the site soils that would fall into <br /> the state category of low risk. Four 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, MW-3, and <br /> L MW-4. The soil sample analyzed from well MW-1 contained MTBE at a <br /> concentration of 99 µg/kg and nondetectable concentrations of TPHg and <br /> BTEX. This concentration is below published Preliminary Remediation <br /> L Goals (PBGs) of 37,000 µg/kg for soil at industrial sites by the Environmental <br /> r Protection Agency Region 9. <br /> L <br /> ❑ Groundwater samples collected during the groundwater monitoring events <br /> 1 indicate low impact to groundwater at the site. The cross-gradient well <br /> L MW-3 did not contain detectable concentrations of constituents associated <br /> I with gasoline. In monitoring well MW-1, TPHg and BTEX were not detected <br /> L and only small concentrations of MTBE were detected during five quarterly <br /> rounds of sampling (5.0, 42.0, 7.7, 4.0, and 8.6 µg/l of MTBE, respectively). <br /> Wells MW-2 and MW-4 contained only trace amounts of MTBE. These <br /> L groundwater concentrations are below SWRCB guidelines for low risk sites. <br /> L <br /> 11 Based on the age of the USTs and period of site operations, the MTBE <br /> detected on site does not appear to have originated from the site operations <br /> and USTs. <br /> L <br /> ❑ Total mass calculations presented in Orion's 1 May 2001 letter estimate that <br /> 1 approximately 30.8 gallons of weathered gasoline remain on site (at a <br /> L density of 6.5 pounds per gallon). <br /> Cl According to the California Water Service, groundwater drinking wells do <br /> L not exist within 2,000 feet of the site. <br /> I <br /> L ❑ The site is paved with concrete and asphalt, reducing the likelihood of <br /> surface water infiltration and the potential for migration of the detected <br /> Lconstituents in the soil to groundwater. <br /> ❑ Evaluation of the CWRCB's guidance document indicates that this site is a <br /> L h low risk classification site and could be closed without requiring any <br /> remedial activities. <br /> L <br /> ? SABF5\5T0CKT0N\LTR\LTR010.D0C 6/27/01 <br /> L <br />