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S Jill A • from CPT-2 at depths of 75, 101, and 120 feet bgs, and from CPT-3 at depths of 74, 100, and 125 feet bgs TPHg and BTEX constituents were not detected above laboratory method reporting limits in the CPT groundwater samples Of the fuel oxygenates analyzed, MtBE and methanol were detected in groundwater sample CPT-2 75 at concentrations of 2 0 and 2,700 ppb, respectively MtBE was detected in CPT-3 100 at a concentration of 6 8 ppb MtBE and TBA were detected in CPT-3 125 at concentrations of 290 and 88, respectively An ozone sparge system was also Installed, connected to the sparge wells, and was brought on-line In December 2002 Groundwater has been monitored and sampled on a quarterly basis from 1991 to the r present During the year of 1997, groundwater was not monitored or sampled SENSITIVE RECEPTORS In April 2001, GR conducted a well search and sensitive receptor survey (SRS) in the vicinity of the subject site The well search was conducted within a %-mile radius around the site Based on the available data supplied by the California Department of Water Resources (DWR), three municipal wells were Identified within the Y2-mile radius of the study area The closest well was located approximately 1,000 feet north-northwest of the site The depths of the three municipal wells were reported to exceed 550 feet bgs, and contain screened intervals beginning at a minimum of 350 feet bgs The SRS was conducted within a 500-foot radius of the subject site The SRS Involved distributing questionnaires to all residences and businesses within the study area, requesting • information about potential groundwater receptors GR distributed 141 questionnairesb via the U S Post Office, and a total of 49 questionnaires (35%) were returned to GR t None of the returned questionnaires indicated the presence of a well within the SRS study area (GR, 2001) MONITORING AND SAMPLINGv TRC's Quarterly Monitoring Report, October Through December 2004 dated January 10, 2005 is included as Attachment A The site has been monitored and sampled since the second quarter 1990 Between 1990 and 1991, the site was monitored and sampled t semi-annually From 1992 to the present, the site has been monitored and sampled quarterly Currently, the monitoring well network consists of wells MW-1 and MW-3 through MW-13, which are monitored and sampled quarterly Samples are analyzed for TPPH, BTEX, and fuel oxygenates by EPA Method 82608 During the fourth quarter 2004, groundwater flow was toward the north at a gradient of 0 002 feet per foot (ft/ft) Maximum reported concentrations of MtBE and TBA during the fourth quarter 2004 were 5 4 ppb (MW-4) and 75,000 ppb (MW-7), respectively Concentrations of MtBE, TPPH, and TBA continue to decline in site monitoring wells MtBE concentrations in wells MW-1, MW-3, MW-4, MW-5, MW-6, MW-7, MWA1, and MW-13 continue to decline (from a historical maximum of 233,000 ppb to a current maximum of 5 4 ppb) TBA concentrations In wells MW-1, MW-3, and MW-7 continue to decline from a historical maximum of 240,000 ppb to a current maximum of 75,000 ppb TBA concentrations in well MW-11 have Increased to a historical high during the third quarter 2004 Based on MtBE and TBA Isoconcentration maps (Figures 5 and 6 in • Attachment A), these constituents are not delineated northeast of the site (in the area of Shell well S-2) 11ConocoPhill ips\Retail Sltes\111921QSSR120041402004 QSSR doc a