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Fourth Quarter 2000 Ground Water Monitoring Report <br /> LIM!jp and Abatement Order No.5-00-707 <br /> 1rAI Pro'ect No. 1232 <br /> 6 4.0 DISCUSSION <br /> 4.1 Ground Water Elevation Contour Maps <br /> Unocal has segregated water at the sites into shallow and deep zones. Figures 3 and 4 present <br /> ground water elevation contour maps for both the shallow (Figure 3) and deep (Figure 4) zones <br /> at the sites. Shallow zone wells extend across the water table and generally are screened from <br /> 30 to 50 feet below grade surface (bgs). Deeper zone wells are generally screened between 50 <br /> and 70 feet bgs. Table 4 and Figure 5 present the well construction details in tabular form and <br /> graphically, respectively. <br /> 4.2 Ground Water Flow Direction and Magnitude <br /> Figure 6 presents the historic ground water flow direction and magnitude for the two sites. <br /> During the summer months, the ground water flow direction for the Wards site is southwest and <br /> for the Unocal site it is generally south to southwest. Figure 6 indicates that during the winter <br /> months when the RIW is not in operation, the natural ground water flow direction is easterly <br /> and during the surnmer months when the RIW is in operation, <br /> ground water flows from both <br /> sites toward the RIW. <br /> 4.3 Shallow and Deep Monitoring Well H dro ra hs <br /> Y g p <br /> FFigures 7 and 8 present hydrographs for selected shallow and deep ground water monitoring <br /> . . wells. These figures also indicate a reversal of ground water flow direction during summer <br /> months when the RIW is in operation. <br /> 4.4 TPH-G and Benzene isoconcentration Maps <br /> Figures 9 and 10 present shallow and deep TPH-G isoconcentration maps for the site, <br /> i.. respectively. Figure 9 indicates the only shallow zone well with detectable concentrations of <br /> TPH-G was MW-22S at a concentration of 359 µg/L. In the deep zone, the highest <br /> concentration of TPH-G was in well MW-3 (19,400 pg/L). <br /> Figures 11 and 12 present shallow and deep benzene isoconcentration maps for the site, <br /> respectively. Benzene was not detected in any shallow zone well during the December 2000 <br /> sampling event. The highest deep zone benzene concentration was in monitoring well MW-3 <br /> at 1,800 pg/L (see Figure 12). <br /> FI <br /> F <br /> Fj <br /> 13M4:1232Roa92 7 <br /> a ENVIRONMENTAL AUDIT, INC.,, <br />