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environ@ <br /> Discussion <br /> Between March 1993 and August 1996 GWE and/or SVE were used to remediate <br /> petroleum hydrocarbons in soil and ground water beneath the site Soil borings drilled in <br /> April 1996 confirmed that petroleum hydrocarbon concentrations in soil had been <br /> remediated Ground water monitoring data indicate that petroleum hydrocarbon <br /> concentrations have been reduced to near detection limits In the second quarter of 1997, <br /> benzene was detected in two wells at concentrations exceeding the MCL of 1 0 ppb Well <br /> RW-1 contained 6 3 ppb benzene following six consecutive quarters of ND results Well <br /> VEW-1 contained 15 ppb benzene following three consecutive quarters of ND results <br /> Based on the ground water chemical data collected since November 1995 and the completed <br /> remediation of petroleum hydrocarbons from the soils, it is our opinion that the low <br /> concentrations of BTEX detected in ground water samples collected during the second <br /> quarter of 1997 will naturally attenuate and should not preclude site closure <br /> Ground water samples from the site have been analyzed for MTBE since May 1996 In <br /> general MTBE concentrations have been increasing at the site over time Shell <br /> discontinued selling gasoline at the site in 1981 prior to the use of MTBE Based on the <br /> increasing MTBE concentration trend and time period during which gasoline was stored at <br /> the site, itis our opinion that the MTBE is originating from an off-site source An ARCO <br /> Service Station is orth This site's locationisshowntonyth00a tachefeet d Clayton <br /> and is a documenteded fuel leak site <br /> Environmental Consultants Plate 2 <br /> HVOCs have been detected in ground water samples collected from Wells MW-2, MW-3, <br /> MW-4, RW-1, RW-2 and VEW-3 The HVOC plume is delineated to the southwest by <br /> Wells MW-1, MW-5, VEW-1, VEW-2, and VEW-4 Wells MW-1 MW-5, VEW-1, <br /> VEW-2, and VEW-4 provide a ND boundary between the former waste oil tank and former <br /> service bays and the HVOC plume It is our opinion that the HVOCs are onginating from <br /> an off-site source The Goodyear Tire and Rubber Company dcumented e is located t 130 or tath El <br /> Doreast, and isado Street, approximately 100 feet to the <br /> incident site (Clayton Environmental Consultants Plate 2) <br /> Ground water beneath the site has been degraded by MTBE and HVOCs Based on site <br /> from off-site sources <br /> data it is our opinion that these <br /> tcontaminants <br /> MTBE and HVOCs ginatindetected in ground waterFurther <br /> investigation and/or remediation of the <br /> beneath the site should be pursued by the responsible party(s) <br /> Based on the information presented in this Preliminary Site Closure Summary, Enviros and <br /> Shell request SJCPHS to conduct a closure evaluation for this site as discussed in <br /> SJCPHS's May 28, 1997 tl tie bepreparedpnrection from SJCPHS and the Central Valley <br /> RWQCB, a closure rep <br /> 97369 3 <br />