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Mr Jeff Wong October 12, 2001 Page 3 of 4 custody documentation are included in Attachment C The estimated extent of benzene and MTBE in the shallow aquifer is presented on Figures 3 and 4, respectively 4.0 SUMMARY Groundwater levels in the shallow aquifer fell an average of 2 83 feet between May 2001 and August 2001 Groundwater flow beneath the site was largely influenced by an apparent groundwater depression near well MW4 Free product was observed in well MW 1 As an interim remedial effort, approximately 23 gallons of product/water mixture were removed and contained on site between August 31 and September 26, 2001 A Ground Zero technician is currently bailing free product from well MW 1 on a weekly bans No gasoline constituents, including MTBE, were detected in well MW5, which is located approximately 100 feet northwest of the former USTs Well MW6, located approximately 130 feet northeast of the former USTs contained only MTBE at 780 ppb TPHg and BTEX were detected in well MW7, located approximately 90 feet east of the fornier USTs, for the first time since the well was installed in October 2000 Well MW8, approximately 120 feet northeast of the former USTs, also contained low levels of toluene and xylenes for the first time Contaminant concentrations are steadily declining in wells MW3 and MW6, but appear to be increasing in wells MW 1, MW2, MW4, and MW7 (first positive results) MW 1 contained free product from at least August 15, 2001 through September 26, 2001, and well MW4 contained MTBE at 32,000 ppb Time versus concentration plots of constituents of concern (TPHg, benzene, MTBE) in site wells are included in Attachment D 5.0 CONCLUSIONS The lateral extent of groundwater contamination beneath the site has been essentially defined, with the exception of the northern extent of the dissolved contaminant plume The decreasing concentrations in site wells north of the former USTs and the incl easing concentration in wells east of the former USTs suggest that the dissolved gasoline plume may be migrating eastward The apparent groundwater depression near well MW4 may be a result of facility well operation or an indicator that some vertical leakage of the shallow aquifer is occurring through the water supply well Dissolved contamination in the upper water-beanng zone does not appear to extend into deeper zones based upon the absence of TPHg, benzene, and MTBE in well MW9B It should be noted, however, that low levels of toluene, ethylbenzene, and xylenes have each been detected at least once during the last three sampling events • 60 RECOMMENDATIONS I Based upon the results of subsurface investigations conducted to date, Ground Zero makes the G 111)aia\GRouNDZE1TuLEBURG\Reports\QMRl3QM2041 doe