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Updated Site Conceptual Model and Third Quarter 2002 Monitoring and Remediation Report Cleanu and Abatement Order No 5-00-707 EAI Pro ect 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 8 and 9 present ground water elevation contour maps for Hydra-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-Stratigraphic 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- 8D, 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 5.2 Ground Water Flow Direction and Magnitude Since the RTW was taken out of operation in August 2000, ground water flow direction in Hydro-Stratlgraphlc 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 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 One exception is TPH-G in well MW-1 i which has shown an increase during the last two quarters Ground water elevation over the same period of time has risen approximately 20 feet on average 5.4 TPH-G and Benzene Isoconcentrahon Maps Figures 10 and 11 present TPH-G isoconcentration maps for Units A and B Figure 10 indicates that three Unit A wells had a detectable TPH-G concentration above the laboratory detection limit of X50 pg/L (MW-14A, 910 pg/L, MW-19S, 280 pg/L, and MW-25S, 340 µg/L) Iii Uillt B, the hzghesi c,omentrdtion of TPH-G was in well MW-11 (49,000 }ig/L) Figures 12 and 13 present Unit A and Unit B benzene isoconcentration maps, respectively Benzene was detected in Unit A in four wells during the September 2002 sampling event (MW- 10A, 078 pg/L, MW-14A, 33 pg/L, MW-19S, 054 pg/L, and MW-25S, 45 pg/L) The highest Unit B benzene concentration was in monitoring well MW-11 at 10,000 pg/L (see Figure 13) BHM WORD 1231RO211 -8- ENVIRONMENTAL AUDIT,INC p