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I 1 1 I r 19 June 2000 ' AGE-NC Project No 95-0103 Page 4 of 5 4 0. DISCUSSION/CONCLUSIONS Based on data collected recently at the site and during site remediation, AGE concludes The relative ground water elevation at the site increased 2 98 feet over the last quarter The map of ground water contours mdicates a divergent ground water flow direction toward the south • Monitoring wells MW-1,MW-2,MW-3,MW-4 and MW-6 had ground water approximately one to seven feet above the top of the screened interval,potentially reducing the effectiveness ' of these ground water monitoring wells to characterize the dissolved-phase hydrocarbon plume in the shallowest ground water ' • The greatest concentrations of petroleum hydrocarbons as gasoline were detected in samples collected from monitoring wells MW-3 and MW-4 and vapor well VE-6 The highest concentrations of benzene were detected in the samples collected from monitoring well MW- ,' 4 and well VE-6 The southern delineation of the dissolved hydrocarbons has not been monitored (south of CHP5 to CHP9), therefore an addition well should be installed • Fuel additives were detected in the ground water samples • An overall reduction of the dissolved-phase hydrocarbon plume concentrations on the site has occurred since ground water monitoring began in 1994 However, the dissolved i hydrocarbon concentrations, specifically benzene have fluctuated over the past four quarters F • In general, contaminant concentrations have increased since vapor extraction and air- ; sparging was discontinued at the site 50 RECOMMENDATION The next quarterly monitoring event should be scheduled for July 2000 • Installation of a ground water monitoring well at the southwestern edge of the site ' Monitoring of the active ground water and soil remediation system Advanced GcoEnvironmcntal Inc V , f