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' The three ground water monitoring wells were monitored quarterly for five quarters prior <br /> to May 1991. Quarterly monitoring results reported benzene, toluene, ethylbenzene, and <br /> xylenes (BTEX) concentrations well below California Action Levels with one exception In <br />' August 1991 benzene at a concentration of 1.3 ppb, was found in well MW-2, but was not <br /> confirmed during any of the four preceding nor three subsequent quarterly monitoring <br /> events <br /> ESE requested site closure from the PHS/EHD on two separate occasions. Site closure was <br /> denied because of the detectable concentrations of petroleum hydrocarbons in the ground <br />' water. In addition, the PHS/EHD requested an additional investigation of soil and ground <br /> water to determine if a source of petroleum hydrocarbons still existed at the site <br />' In May 1993 ESE drilled two soil borings in th <br /> Y g e vicinity of boring B-2Y and one monitoring <br /> well was installed downgradient and to the west of the former tank excavation This <br /> additional investigation work was documented in a report dated June 11, 1993. Analyses ' <br /> of soil samples collected during the investigation were reported as nondetectable for TPH-D <br /> and benzene, toluene, ethylbenzene, and xylenes (BTEX). Analyses of ground water <br /> samples from the new monitoring well, MW-4, were also reported as nondetectable for <br /> TPH-D and BTEX. In addition, in May 1993 and July 1993 ground water sampling was <br />' performed on the three existing wells. Analysis of ground water from well MW-1 showed <br /> detectable concentrations of TPH-D of 950 micrograms per liter (ug/L) in May and 200 <br />' ug/L in July 1993. BTEX was nondetectable for the existing wells for both events. <br />' 1.2 UARTERLY ACnVMES <br /> The following tasks were performed at the site during this quarter: <br /> • On September 23, 1993, ESE measured the depth to ground water and collected <br />' ground water samples from wells MW-1 through MW-4, <br /> • The ground water samples were analyzed for TPH-D and BTEX, and <br />' The data were evaluated and this report was prepared. <br /> Environmental Science <br /> F,692500913gmr 993 2 &Engineering.Inc <br />