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Updated Site Conceptual Model and Second Quarter 2002 Monitoring and Remediation Report Cleanup and Abatement Order No 5-00-707 p EAI Project No 1232 50 DISCUSSION i5.1 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 P Y 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 8 and 9 present ground water elevation contour snaps for Hydro-Stratigraphic 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 round water g � g ter flow direction in Hydro-Stratigraphic Units A and B has consistently been toward the east The current gradient as measured from Unit B is approximately 0 003 foot/foot 5.3 Monitoring Well Hydrographs Figures 4 through 7 present TPH-G and benzene concentrationlu p s 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 10 and 11 present TPH-G is o concentration maps for Units A and B Figure 10 indicates that one Unit A well had a detectable TPH-G concentration above the laboratory detection limit of <50 µg/L (MW-19S at 190 pg/L) In Unit B, the highest concentration of TPH-G was also in well MW-11 (37,000 }ig/L) Figures 12 and 13 present Unit A and Unit B benzene isoconcentration maps, respectively Benzene was not detected in Unit A wells during the Tune 2002 sampling event The highest Unit B benzene concentration was in monitoring well MW-1 I at 8,600 gg/L (see Figure 13) r13HM 1232RO231 -7- ENhIRONMENTAL AUDIT, INC 1