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VVL' INC 4 The groundwater treatment system has removed approximately 388,800 gallons of • hydrocarbon-contaminated groundwater from the subsurface using best available technology provided by a pump and treat system using monitoring well MW-1 as the extraction well This effort is estimated to have removed the following estimated volumes of petroleum hydrocarbon constituents by carbon filtration 2 15 gallons of total petroleum hydrocarbon as gasoline, 0 12 gallons of benzene, 0 13 gallons of toluene, 0 09 gallons of ethylbenzene and 0 42 gallons of xylene Although the system removed the above-mentioned volumes of petroleum hydrocarbon compounds, it did not modify the groundwater flow gradient as determined by groundwater surface elevations measured from the monitoring wells during the period of operation from September 1992 to June 1994 No effect on the groundwater surface elevation was found from operational pumpage from the main water supply well The groundwater treatment system has not been active since June 1994 5 The remaining hydrocarbon constituent within the groundwater at monitoring well MW-1 is benzene and it is estimated to be present at concentrations of less than five µg11 This very low level concentration of benzene does not pose a threat to the groundwater of the state or deprive the beneficial use of the groundwater beneath the site No significant threat to the drinking water supply beneath the site or immediate surrounding area is present because 1) the groundwater production zones for the onsite main water supply well and standby wel I are from deeper zones, 2) a clay layer is present that is at least five feet thick and has been depicted by McLaren (1989a) to extend throughout the site, minimizing downward movement of potentially contaminated groundwater, 3) the groundwater gradient determined from the monitoring well network has not produced a gradient in the direction of the main water supply well, indicating that the shallow zones completed with the monitoring awell network is hydrodynamically separate from the deeper zone in the main water supply well, and 4) the nearest offsite domestic water supply well is approximately 19150011005 43