SITE INFORMATION AND CORRESPONDENCE

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Monitoring wells 4 and 5 were installed in 1989. Initial Benzene concentrations were ND. Benzene has been detected more frequently in MW-4 and if one looks at gasoline concentrations it is obvious that MW-5 is a zero line well and MW-4 is at the downgradient lateral extent of the plume. On February 26, 1992 the three vapor wells were installed . The clustered wells VW2 and VW3 were apparently located based on data from KBS. VW2 is screened from 51-24 and VW3 is screened from 10-25. KB-5 showed highest concentrations at total depth of 20 feet. The estimated vertical extent of soil contamination in this area is deeper than 52 feet based on analytical data from VW-2. Water was encountered at 52 feet . VW1 was installed apparently based on data from KB3. Analytical data was ND for all samples from the installation. MW-6 and MW-7 were installed during the same week as the vapor wells. Soil samples were ND. Groundwater samples from MW-7 were ND. MW-6 showed concentrations of hydrocarbons in groundwater until May 8 1996. MW-8 and MW-9 were installed on July 19, 1994 to a depth of 54 feet_ Static water in both wells was 43 feet. The wells were screened from 30-54 feet. Analytical soil results of these two wells were ND. Groundwater analytical showed approximately 90-100 ppb gasoline and Benzene as ND. Laboratory notes on these analyses state that the contamination does not appear to be gasoline. Groundwater elevations have changed significantly. In 1988 static groundwater was 30 feet , in 1992 static water level was 50 feet and current static groundwater level is 30. Monitoring wells 1,9,8,7 and 5 have always been clean. Wells 2,3 and 4 have always been contaminated. MW-6 had levels of contamination from March 4 1992 until February 8, 1996. MW-6 is the only well which appears to be naturally attenuating . Current Benzene level is ND.. When water elevations are plotted and compared to gasoline (TPHg) concentrations it appears that 90% of the attenuation occurred while groundwater was at a stable elevation (November 12, 1993). When plotting Benzene and groundwater elevation for MW-2 there is a correlation that indicates dilution is occurring. Closure has been denied based on the following rational: 1) The plume is approximately 150 feet by 60 feet . Concentrations in the center of the plume (MW2) of benzene are in the range of 1200 ppb. 2) Soil beneath the dispensers was treated by a pilot vapor extraction system (VES) that went asymptotic. When the VES wells were installed groundwater was at 52 feet. When the system was initialized groundwater was at 37 feet.