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Updated Site Conceptual Model and First Quarter 2003 Monitoring and Remediation Report Cleanup and Abatement Order Na S-DO-707 „_ __ ,,_ EAI Project No 1232 5.0 DISCUSSION 5.1 Ground Water EIevation Contour Maps Ground water beneath the sites has been segregated into shallow and deep zones hereinafter referred. to Hydro-Strati graphic 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 (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-8D which is screened in Unit D Figures 8 and 9 present ground water elevation contour maps for Hydro-Stratigraphic Units A and B Unit A wells are screened across the water table, generally between 30 to 50 feet bgs Unit B wells are generally screened between 50 and 70 feet bgs (Figures 8 and 9) 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- 81), MW-23D and MW-24D) are screened in Unit D (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 iSince the RIW was taken out of operation in August 2000, ground water 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 0 002 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 Ground water elevation over the same period of time has risen approximately 20 feet on average Note during this sampling period, construction materials were on well MW-2 Therefore, ground water monitoring well MW-2 could not be gauged, purged, or sampled dun-ng the current monitoring event 5.4 TPH-G and Benzene Isoco nce nt ration Maps Figures 10 and 11 present TPH-G isoconcentration maps for Units A and B Figure 10 indicates that only Unit A wells MW-19S (73 pg/L) and MW-25S (220 lig/L) had a detectable TPH-G concentration above the laboratory detection limit for the first quarter 2003 In Unit B, the highest concentration of TPH-G was in well MW-3 (21,000 Pg/L) Figures 12 and 13 present Unit A and Unit B benzene isoconcentration maps, respectively Benzene was detected in Unit A only in well MW-14A (3 4 lig/L) during the February 2003 The highest Unit B benzene concentration was in monitoring well MW-3 at 3,700 pg/L (Figure 13) 1 sHM worm 1232RO321 -8- ENVIRONMENTAL AUDIT, INC