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Second Quarter 2001 Ground Water Monitoring Report !Qeariu2 and Abatement Order No 5-00-707 CA1 Project No 1232 4.0 DISCUSSION 4.1 Ground Water Elevation Contour Maps ' Unocal has segregated water at the sites into shallow and deep zones All Ward wells are screened in the Unocal deep zone Figures 3 and 4 present ground water elevation contour snaps for both the shallow(Figure 3) and deep (Figure 4) zones at the sites Shallow zone wells extend across the water table and generally are screened from 30 to 50 feet below grade surface (bgs) Deeper zone wells are generally screened between 50 and 70 feet bgs Table 4 and Figure 5 present the well construction details in tabular form and graphically, respectively Two additional wells designated as shallow (MW-23S and MW-24S) are screened between approximately 85 and 90 feet bgs and two additional wells designated as deep (MW-23D and MW-24D) are screened between approximately 98 to 103 feet bgs The shallow and deep screened intervals in these four wells do not correspond to the shallow and deep intervals in the other wells Therefore, data obtained from these four wells are not included in the shallow or deep zone ground water elevation maps or isoconcentration maps 4.2 Ground Water Flow Direction and Magnitude Figure 6 presents the historic ground water flow direction and magnitude for the two sites During the summer months, the ground water flow direction for the Wards site is southwest and for the Unocal site it is generally south to southwest Figure 6 indicates that during the winter months when the RIW is not in operation, the natural ground water flow direction is easterly and during the summer months when the RIW was formerly in operation, ground water flows from both sites toward the RIW 4.3 Shallow and Deep Monitoring Well Hydrographs Figures 7 and 8 present hydrographs for selected shallow and deep ground water monitoring wells These figures also indicate a reversal of ground water flow direction during summer months when the RIW was formerly in operation 4.4 TPH-G and Benzene Isoconcentration Maps Figures 9 and 10 present shallow and deep TPH-G isoconcentration maps for the site, respectively Figure 9 indicates that one shallow zone well had a detectable TPH-G concentration above the laboratory detection limit of <50 µg/L (MW-18 at 50 µg/L) In the deep zone, the highest concentration of TPH-G was in well MW-25D (32,300 µg/L) Figures 11 and 12 present shallow and deep benzene isoconcentration maps for the site, respectively Benzene was detected in two shallow zone wells during the May 2001 sampling event (MW-10A at 12 µg/L and MW-18 at 4 2 µg/ L) The highest deep zone benzene concentration was in monitoring well MW-25D at 2 500 µg/L (see Figure 12) ' BHM 123280151 7 ENVIRONMENTAL AUDIT, INC