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elevation decreases from the northwest (well S-3) to the southeast (well L-1). Groundwater <br />elevations range between 5034.4 feet above mean sea level (ft amsl) and 5010.9 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/ft). Thus, the existing groundwater level data suggest that <br />the slurry wall has not affected the regional groundwater flow pattern. However, local <br />groundwater flow directions have changed in the immediate vicinity of the slurry wall. <br />5.3 Seasonal Groundwater Level Fluctuations <br />Prior to comparing pre- and post-slurry wall groundwater levels, it is important to understand the <br />seasonal groundwater level fluctuations that occur in the area of the Stegner Farm mine. <br />Seasonal groundwater level fluctuations occur at all of the Stegner Farm and LaFazge wells <br />considered in this evaluation. Seasonal groundwater level fluctuations are best shown by the <br />LaFarge well hydrographs as these wells have the longest monitoring record. Figure 9 are <br />hydrographs that show groundwater levels at four (4) LaFarge wells for the entire monitoring <br />period (February 1998 through December 2001). The time period shown in Figure 9 represents <br />both pre- and post-slurry wall conditions. Groundwater level data depicted in this figure aze <br />primarily shown to illustrate the seasonal changes in groundwater elevation over an approximate <br />4-yeaz monitoring period and the impacts of seasonal irrigation on groundwater levels. <br />Groundwater elevation changes shown in Figure 9 indicate that groundwater levels at these wells <br />fluctuate seasonally. Four seasonal groundwater elevation "highs" aze shown on the graph. The <br />highest groundwater elevations shown on these hydrographs correspond to the annual irrigation <br />period and is a direct response to seepage of irrigation water from the ditch and percolation from <br />flood irrigation to the shallow water table. Groundwater levels increase once imgation begins, <br />usually in May or June, and decrease after imgation ends, usually in early September. <br />Wells L-2, L-3, and L-5, which are located immediately adjacent to local irrigation ditches, show <br />groundwater elevation increases during the summer irrigation season. Groundwater levels at well <br />L-1, which is not located next to an irrigation ditch also increase during the imgation season, <br />except during the summer of 2001. It is notable that groundwater levels in wells L-2, L-3, and L- <br />5 increased (as usual) during the summer of 2001 while the groundwater leve] in well L-1 <br />decreased during the same period. This abnormal groundwater level decrease at well L-1 while <br />groundwater levels at the other wells increased suggests the possibility of groundwater <br />withdrawal in the vicinity of L-1 during the summer of 2001. <br />10 <br />