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' 18 October 2002 AGE-NC Project No 95-0128 ' Page 6 of 7 ' 4.4. SUMMARY AND CONCLUSIONS The following conclusions were drawn from the results of this quarterly investigation • Ground-water elevations measured during the August 2002 monitoring event ranged between 20 01 and 2177 feet below MSL, ground water flow direction at the site was Inferred to be ' northeast towards a well-defined cone of depression at extraction well EW-1 • Dissolved petroleum hydrocarbons quantified as TPH-g,TPH-d and BTEX compounds were detected in ground water samples MW-4, MW-5 and VW-1, collected within the ' northeastern portion of the site • The highest concentrations benzene (160 pg/1), toluene (170 µg/1) and ethylbenzene ' (1,900 gg/1) were detected in sample MW-5, these concentrations were above the DHS' Maximum Contaminant Levels (MCLs) in drinking water • The highest concentration of MTBE detected in the ground water samples (690 µg/1) occurred in monitoring well MW-5, adjacent to extraction well EW-1 Lower or non- detectable MTBE concentrations in the down-gradient and cross gradient wells defined the lie dissolved MTBE plume toward the north and west(Figure 4) The dissolved MTBE plume has not been defined east of well MW-15 • The lead scavenger 1,2-DCA was detected in sample MW-3 at 15 gg/l, slightly above the MCL of 0 5 gg/l • Approximately 0 18 kg or 0 39 lbs of MTBE, 0 16 kg or 0 35 lbs of benzene and 2 2 kg or 4 9 lbs of TPH-g were removed from the site and treated by the ground water extraction system I 5.0. RECOMMENDATIONS ' Based on the results of this and previous investigations, AGE recommends • Continued quarterly ground water monitoring of the site concurrently with the Pacific Car Wash site (4405 Pacific Avenue), the next monitoring event is tentatively scheduled for November 2002 I • Continued interim ground water extraction and treatment as a remedial measure, with the addition of another ground water extraction well by well MW-5 I • Assessment of the dissolved MTBE cast of wells MW-15 and MW-16 • IAdvanced GeoEnvironmental Inc