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The three ground water monitoring wells were monitored quarterly for five quarters prior to May 1991 Quarterly monitoring results reported benzene, toluene, ethylbenzene, and xylenes (BTEX) concentrations well below California Action Levels with one exception. In August 1991 benzene at a concentration of 1.3 ppb, was found in well MW-2, but was not confirmed during any of the four preceding nor three subsequent quarterly monitoring events. ESE requested site closure from the PHS/EHD on two separate occasions. Site closure was denied because of the detectable concentrations of petroleum hydrocarbons in the ground water. In addition, the PHS/EHD requested an additional investigation of soil and ground water to determine if a source of petroleum hydrocarbons still existed at the site. In May 1993, ESE drilled two soil borings m the vicinity of boring B-2Y and one monitoring well was installed downgradient and to the west of the former tank excavation. This additional investigation work was documented in a report dated June 11, 1993. Analyses of soil samples collected dunng the investigation were reported as nondetectable for TPH-D and benzene, toluene, ethylbenzene, and xylenes (BTEX). Analyses of ground water samples from the new monitoring well, MW-4, were also reported as nondetectable for TPH-D and BTEX. In addition, in May 1993 and July 1993 ground water sampling was performed on the three existing wells Analysis of ground water from well MW-1 showed detectable concentrations of TPH-D of 950 micrograms per liter (ug/L) in May and 200 ug/L in July 1993. BTEX was nondetectable for the existing wells for both events. 1.2 QUARTERLY ACTIVITIES The following tasks were performed at the site during this quarter: • On September 23, 1993, ESE measured the depth to ground water and collected ground water samples from wells MW-1 through MW-4, • The ground water samples were analyzed for TPH-D and BTEX, and • The data were evaluated and this report was prepared. Environmental Science F\6925009\3gmr 993 2 &Engineering,Inc