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1.2 Chronology of UST-Related Events ' A 1,000-gallon gasoline UST located beneath the sidewalk along South Center Street, an associated fuel dispenser located within the building, and the portion of product piping from the UST to the building were removed in ' December 1990 The remaining product piping, from the edge of the building to the former dispenser, was properly abandoned on April 17, 1998 ' On April 16, 1998, two 1-inch diameter direct-push probeholes were driven beneath the former UST to collect soil and groundwater samples for laboratory analysis Analytical results, summarized in the June 2, 1998 Preliminary Subsurface Site Investigation Results and Product Piping Abandonment Completion Report, indicated benzene, toluene, ethylbenzene, and xylenes (BTEX) impact to subsurface soil and groundwater The soil and ' groundwater samples did not contain detectable oxygenate compounds In July 1999, Ground Zero Analysis, Inc (GZA) of Escalon, California, I performed a subsequent subsurface investigation GZA drilled three soil borings, completed them as groundwater-monitonng wells (MW-1, MW-2, and MW-3), and collected soil and groundwater samples for laboratory analysis GZA's Investigation, summarized in their July 28, 1999 Groundwater Monitoring Well Installation Report, detected BTEX and total petroleum hydrocarbon as gasoline (TPH-G) impact in soil and groundwater samples collected at MW-2 Samples collected from MW-1 and MW-3, placed in hydraulically upgradient positions relative to the former UST, did not contain detectable petroleum hydrocarbons ' The SJCEHD required quarterly groundwater-monitoring be performed to assess contaminant trends, which Included the oxygenate analytes tert-butanol ' (TBA), methyl-tert-butyl ether (MTBE), di-isopropyl ether (DIPE), ethyl-tert- butyl ether (ETBE), and tert-amyltnethyl ether (TAME) After several quarterly events, the laboratory analytical data indicated that higher concentrations of petroleum hydrocarbons were detected in samples collected from well MW-2 and non-detectable or lower concentrations were measured at the upgradient locations SJCEHD requested that additional investigation be performed to assess the extent of petroleum Impact PSC submitted a September 24, 2001 Subsurface ' Site Investigation Workplan to SJCEHD, which proposed further assessment SJCEHD approved this work plan in a letter dated October 16, 2001 PSC performed an investigation in March 2002 Six probeholes (PH-3 through PH-8) were advanced, one groundwater-monitoring well (MW-4) was installed, one air-sparging well (SP-1) was constructed, one soil-vapor- extraction well (VW-1) was constructed, and samples of soil and groundwater were collected for laboratory analysis Investigation findings were submitted ' z Quarterly Groundwater Monitoring Report May 2005 Prepared for SARA LEE BAKERY GROUP,INC Prepared by Philip Services Corporation lnvertigatrve and Quarterly Report\2nd Quarterly Report 05_2005(final) September 23,2005