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S EC ® R h� . 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 Environmental Protection Agency (EPA) Method 8260 According to the SJCEHD, 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, GRI oversaw the installation of groundwater monitoring wells MW-12 and MW-13, the installation of 10 ozone sparge (OS) points (SP-A through SP-H, SP-J, and SP-K, Attachment 1) 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 soil stratigraphic log of the boring by comparing the CPT tip resistance to sleeve friction on the CPT cone TPHg and 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 OS system was installed, connected to the sparge wells, and was brought on-line on • December 20, 2002 by GRI The currently operating OS system 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 Monitoring Well, CPT, and Ozone Microsparge System Installation Report, May 2003) The monitoring well network consists of 12 wells (MW-1 and MW-3 through MW-13) that are sampled quarterly Quarterly groundwater monitoring and sampling of the site wells is coordinated with the groundwater monitoring and sampling of the wells located at and in the vicinity of the nearby Shell Service Station (1267 Country Club Boulevard) SENSITIVE RECEPTORS A water supply well survey was performed in 1989 Results 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 In April 2001, GRI conducted a well search and sensitive receptor survey (SRS) within a '/-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 '/-mile radius of the site The closest well was located approximately 1,000 feet north- northwest of the site A 500-foot radius, door-to-door SRS was also conducted, which involved the distribution of questionnaires to residences and businesses within the site x area None of the returned questionnaires indicated the presence of a water supply well within 500 feet of the site (GRI, Monitoring Well Installation Report, September 26, . 2001)