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• Shell Service Station, 4445 North Pershing Avenue In 1990, USTs were removed and subsequently replaced in another location TPH-g and benzene were detected in soil samples collected from beneath the former USTs at concentrations of 4,300 and 10 mg/kg, respectively Groundwater monitoring wells MW I through MW3, and vapor extraction wells VEW-1 and VEW-2 were installed in 1990 Groundwater monitoring wells MW 1 through MW3 were installed either upgradient or cross ' gradient of potential source areas An additional onsite well, MW4, was installed in 1991 A pilot soil vapor extraction test was performed from December 1991 to January 1992 A soil sample collected at 28 5 feet bgs during the installation of ExxonMobil well MW8, which was installed downgradient of the Shell dispenser islands, contained 3,200 mg/kg TPH-g and 12 mg/kg benzene Groundwater samples collected from ExxonMobil well MW8, as presented in Table 1, have contained up to 120,000 gg/L TPH-g (April 1988) and 1,100 ' gg/L benzene (February 1993) As presented in the hydrograph for MW8 (Appendix C), and in Table 1, the concentrations in groundwater collected from MW8 in March 2002 decreased to 215 gg/L TPH-g, and 0 60 gg/L benzene SJCEHD granted site closure for this site in ' November 2002 (Appendix D) Though the analytical results of samples collected from MW8 were not included in the closure documents, SJCEHD considered the environmental investigation of this Shell service station complete and issued a "letter of no further action" ' regarding the Shell site A figure presenting the site configuration of the Shell service station, as well as soil and groundwater analytical tables, and regulatory correspondence, is ' provided in Appendix D 7-Eleven Site No. 17334, 4501 North Pershing Avenue. ' In 1997, seven geoprobe bonngs (GPI through GP7) were advanced onsite Benzene was detected in soil sample GP4 at 17 feet bgs at 0 0095 mg/kg MTBE was detected in soil sample GPI at 15 feet bgs at a concentration of 0 91 mg/kg Up to 9,100 gg/L benzene, 150,000 gg/L TPH-g, and 84,000 gg/L MTBE were detected in grab groundwater samples collected from GP4 Five groundwater monitoring wells were installed onsite Soil samples ' collected during the installation of ExxonMobil well MW9, which was installed downgradient of the 7-Eleven site, did not contain detectable concentrations of TPH-g or benzene Groundwater samples collected from ExxonMobil well MW9, as presented in ' Table 1, have contained up to 35,000 gg/L TPH-g, 4,900 gg/L benzene, and 250 gg/L MTBE Groundwater concentrations in MW9 have decreased to below laboratory reporting limits for both TPH-g and benzene MTBE was detected at a concentration of 150 gg/L, ' when the well was last sampled on 6 March 2002 The highest detected concentration of MTBE at the 7-Eleven site during the most recent sampling event was 1,100 gg/L (MW4 10/15/02) A figure presenting the site configuration of the 7-Eleven service station, as well ' as soil and groundwater analytical tables, is provided in Appendix E 1 ' G UPrgecu\73942\MAS7ER\WP\VM3031WPta dm 6