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Updated Site Conceptual Model and First Quarter 2002 Monitonng and Reanediation Report Cleanup and Abatement Order No 5-00-707 EAI Protect No 1232 5.0 DISCUSSION 5.1 Ground Water Elevation Contour Maps Ground water beneath the sites has been segregated into shallow and deep zones hereinafter referred to Hydro-Stratigraphic Units A, and B respectively, or simply Unit A and Unit B Two deeper units, Unit C and Unit D, are also associated with the sites (see Section 2 0) The wells that are located on the former Wards site are generally screened in Unit B with the exception of well MW-81) which is screened in Unit D Figures 11 and 12 present ground water elevation contour maps for Hydro-Strati graphic Units A and B Unit A wells extend across the water table and generally are screened from 30 to 50 feet bgs Unit B wells are generally screened between 50 and 70 feet bgs Five additional wells are screened across Hydro-Strati graphic units deeper than Units A and B as follows Two wells are screened in Unit C (MW-23S and MW-24S) and three wells (MW- 81), MW-23D and MW-24D) are screened in Unit D (see Section 2 0) It is EAI's opinion that Units C and D are hydraulically connected and represent the same unit 52 Ground Water Flow Direction and Magnitude Since the RIW was taken out of operation in August 2000, ground water flow direction in Hydro-Strati graphic Units A and B has consistently been toward the east The current gradient as measured from Unit B is approximately 0 002 foot/foot 5.3 Monitoring Well Hydrographs Figures 7 through 10 present TPH-G and benzene concentration plus ground water elevation verses time for ground water monitoring wells MW-2, MW-3, MW-11 and MW-12, respectively A general decline in TPH-G and benzene concentrations has been observed since ground water monitoring was initiated Ground water elevation over the same period of time has risen approximately 20 feet on average 54 TPH-G and Benzene Isoconcentration Maps P Figures 13 and 14 present TPH-G isoconcentration maps for Units A and B Figure 13 indicates that one Unit A well had a detectable TPH-G concentration above the laboratory detection limit of <50 gg/L (MW-25D at 85 gg/L) In Unit B, the highest concentration of TPH-G was also in well MW-25D (49,000 pg/L) Figures 15 and 16 present Unit A and Unit B benzene isoconcentration maps, respectively Benzene was not detected in Unit A wells during the March 2002 sampling event The highest Unit B benzene concentration was in monitoring well MW-25D at 2,000 gg/L (see Figure 16) BHM 1212RO231 -9- ENVIRONMENTAL A UDIT INC