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Closure Report - Chevron Station 119-1848 <br /> January 18, I999 <br /> uses of the groundwater in the site vicinity are not likely to be impacted <br /> Engineered remediation of impacted groundwater was not undertaken at the site The <br /> dissolved petroleum hydrocarbon plume has remained stable since the subsurface <br /> facilities were removed or replaced Moreover, it appears the hydrocarbon plume has <br /> not migrated off-site as evidenced by the non-detectable concentrations of TPHg, <br /> benzene, and MTBE in the grab groundwater samples coIIected from the four off-site <br /> borings The low concentrations of petroleum hydrocarbons left in place during the <br /> UST removal do not appear to be acting as a continuous source impacting groundwater <br /> VIII Sign-off <br /> Some impacted soil remains in place near the former gasoline UST pit, southern <br /> dispenser island, and the current UST pit. <br /> Historical groundwater monitoring data indicate that TPHg, benzene, and MTBE <br /> concenttations have been detected in monitoring wells C-1 and C-2 Benzene has been <br /> detected in well C-1 three times in the last ten sampling events at a concentration high <br /> of 15 ppb furthermore, benzene has been detected in well C-2 twice in the last ten <br /> sampling events at a concentration high of 1 0 ppb Concentrations of MTBE in well <br /> C-1 have remained consistently low since May 1996 The concentration high in well <br /> C-1 was 7 8 ppb MTBE concentrations detected in well C-2 have declined steadily <br /> since August 1996 from a high of 2,100 ppb to fib ppb detected in the August 1998 <br /> sampling event TPHg have not been detected in well C-3 since January 1992, nor has <br /> benzene been detected since November 1992 MTBE has never been detected in well <br /> C-3 <br /> Based on the lack of detectable petroleum hydrocarbons in the soil or groundwater from <br /> the off-site soil borings, the Iack of any existing or potential sensitive receptors in the <br /> vicinity of the site, and the likelihood that the existing or potential beneficial uses of the <br /> groundwater beneath the San Joaquin River Basin will not be impacted by petroleum <br /> hydrocarbons from the subject site, further investigative, remedial, or monitoring <br /> activities at this site are not warranted and this site should be closed by the SJCPHS and <br /> California Regional Water Quality Control Board-Central Valley Region <br /> M346392 02-cl 6 <br />