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S E C ® R a alternative for this site (SECOR, Dual Phase Extraction Summary Report, February 2002) On April 23, 2002, the SJCEHD expressed concern with high concentrations of tertiary butyl alcohol (TBA) in wells MW-3 and MW-7 On May 9, 2002, GRI confirmed the presence of high concentrations of TBA in the wells (over 200,000 µg/L), and attributed the raised concentrations to MtBE metabolism In correspondence dated July 22, 2002, the SJCEHD required that the groundwater samples from wells MW-3 and MW-7 be analyzed for the full scan of analytes by EPA Method 8260 According to the SJEHD, other degradation constituents are likely present if MtBE metabolism is occurring in the areas of wells MW-3 and MW-7 GRI began sampling MW-3 and MW-7 for the full scan of analytes by EPA Method 8260 during the first quarter 2003 In December 2002, GRE oversaw the installation of groundwater monitoring wells MW-12 and MW-13, the installation of 10 sparge points (SP-A through SP-H, SP-J, and SP-K) completed at a depth of 30 feet bgs, and drilled two additional CPT probes (CPT-2 and CPT-3) to a maximum depth of 140 feet bgs The CPT rig was equipped with an on- board computer system that provided a real time analysis of the subsurface conditions The CPT device created a lithologic log of the boring by comparing the CPT tip resistance to sleeve friction on the CPT cone TPHg and benzene, toluene, ethylbenzene, and xylene (BTEX) constituents were not detected above laboratory method reporting limits in the CPT groundwater samples MtBE and methanol were • detected in the 75-foot groundwater sample from CPT-2 at concentrations of 2 0 and 2,700 ppb, respectively MtBE was detected in the 100-foot groundwater sample from CPT-3 at a concentration of 6 8 ppb MtBE and TBA were detected in the 125-foot sample from CPT-3 at concentrations of 290 and 88 ppb, respectively (GRI, Groundwater Monitoring Well, CPT, and Ozone Microsparge System Installation Report, May, 2003) An ozone sparge (OS) system was installed, connected to the sparge wells, and was brought on-line on December 20, 2002 by GRI Operation of the OS system is currently ongoing and consists of a K-V Associates (KVA) "C-Sparge" ozone microsparging system that cycles a mixture of ozone and air into each sparge point for five to 15 minute periods, approximately 16 times per day (GRI, Groundwater Monitonng Well, CPT, and Ozone Mfcrosparge System Installation Report, May, 2003) Groundwater from the site wells has been monitored and sampled since 1990 SENSITIVE RECEPTORS A water supply well survey was performed in 1989 indicated the presence of one private water supply well located approximately 900 feet from the site (direction unknown), and one public water supply well located 1,100 feet northwest of the site 4 In April 2001, GRI conducted a well search and sensitive receptor survey (SRS) within a Xz-mile radius of the site Based on the available data supplied by the California Department of Water Resources (DWR), three municipal wells were identified within the , • '/z-mile radius of the study area The closest well was located approximately 1,000 feet " A north-northwest of the site A 500-foot radius, door-to-door SRS was also conducted, 1 1ConocoPhilhps%Retaii Sites1111921QSSR120051102005 QSSR and QRPS doc