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CAM BRIA thick that are present between shallow groundwater at the subject site and the top of the screened interval for Well No 12 These clay layers should provide a significant barrier between any petroleum hydrocarbons that may be found in the shallow groundwater and the water bearing sediments at 210 fbg in Well No 12 Former Chevron Service Station This former service station is located northeast (and upgradient) of the subject site at the address of 301 West Kettleman Lane, with cross streets, west and east of the site, of South Lee Avenue and South Pleasant Avenue A site map showing the location of the former Chevron site in relationship to the subject site is presented in Appendix F of this report and on Figure 3 During removal of the USTs and associated dispensers and piping (August 1998), hydrocarbons were detected in the soil beneath the site Since then 14 shallow groundwater monitoring wells and 5 deeper monitoring wells have been installed in the vicinity of this site The site is currently under a Cleanup and Abatement Order issued by the RWQCB on April 20, 2000 Quarterly groundwater monitoring data from the Chevron site indicates the groundwater flow direction is generally to the southwest A comparison of groundwater elevation data from Chevron's shallow wells and deep wells suggests the vertical gradient at the site is downward Gettler-Ryan (GR) monitored water levels in site monitoring wells for a three-day period and determined that groundwater elevation at the site fluctuates in daily cycles corresponding to the operation of municipal well No 12 These findings are documented in GR's November 2, 1999 Offstte Source Survey The highest benzene and MTBE concentrations in groundwater at the former Chevron site have been detected in the vicinity of the former USTs at concentrations of 39,000 ppb and 720,000 ppb, respectively The concentration of MTBE in Chevron's well MW-5, located in the southwest corner of the site, was 3,650 ppb in March 2000 (Figure 3) This concentration is three times higher than the previous sampling event in this well Well MW-5 is located downgradient of the former UST and data from this well essentially represents the concentration of MTBE that is moving offsite Chevron's well MW-8 is located south-southeast of Chevron's well MW-5, on the southern side of West Kettleman Lane, adjacent to the Shell site This well has not contained detectable levels of petroleum I hydrocarbons or fuel oxygenates A table of historical groundwater analytical data and a site • map from SECOR International, Inc 's July 24, 2000 Problem Assessment Report are included in Appendix F 1346 6