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elevations range between 5032.9 feet above mean sea level (ft amsl) and 5010.6 ft amsl at wells <br />S-3 and L-1, respectively. Recognizing that groundwater moves from high to low elevation, <br />groundwater flows from the northwest to the southeast across the area at a gradient of <br />approximately 0.005 feet per foot (ft/fQ. <br />5.2 Post-Slurry Wall Groundwater Levels <br />Post-slurry wall groundwater conditions were also evaluated using monthly groundwater <br />monitoring data collected at the Stegner Farm and LaFazge wells between May 2000 and <br />December 2001. Groundwater level hydrographs were prepared using these data to show <br />changes in groundwater elevation after the construction of the Stegner Farm slurry wall. The <br />post-slurry wall hydrographs for both the Stegner Farm and LaFazge wells are shown as Figure <br />7. <br />Examination of Figure 7 shows that groundwater levels in the Stegner Farm wells, which are <br />generally located within 100 feet or less from the slurry wall, have changed since the slurry wall <br />was installed. When examining Figure 7, consider that Stegner Farm wells S-1, S-2, S-3, S-4, S- <br />7, and S-8 are upgradient ("upstream") of the slurry wall; whereas wells S-5 and S-6 are <br />downgradient ("downstream") of the slurry wall. All of the LaFazge wells are located <br />downgradient of the slurry wall at distances ranging between 1,400 and 2,600 feet. <br />Figure 7 shows seasonal groundwater level increases and decreases at both the Stegner Farm and <br />LaFazge wells. The highest groundwater levels occur following spring rain events and the <br />summer irrigation season. The lowest groundwater levels occur during the winter season when <br />precipitation and irrigation rechazge is not available. The groundwater level fluctuations between <br />the spring/summer and winter months is typically about 4 feet. Hydrographs for wells S-1, S-2, <br />S-3, S-4, S-7, and S-8 show evidence of groundwater level increases since the slurry wall was <br />installed. Similarly, hydrographs for wells S-5 and S-6 show groundwater level decreases since <br />the slurry wall was installed. The groundwater level changes at wells S-1 through S-8 aze <br />expected as these wells are located immediately adjacent to the slurry wall where its effect on <br />groundwater levels would be most noticeable. <br />Figure 8 is a potentiometric map that shows the elevation of the water table in the Stegner Farm <br />area in April 2001, one year after slurry wall construction was initiated. This map was prepared <br />using groundwater elevation data from both the Stegner Farm and LaFarge monitoring weAs, a <br />total of 12 wells. Each contour line shown on the map represents a line of equal water level <br />elevation. The groundwater flow pattern shown on Figure 8 (post-slurry wall) is similar to that <br />shown on Figure 6 (pre-slurry wall) for April 2000. Figure 8 shows that the groundwater <br />9 <br />