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<br />' S.3 Historic Aquifer Water Level Data <br />' In order to understand the historic storage function of the alluvial aquifer in the mined area, water <br />' level data were analyzed. The data were collected from 38 piezometers installed at the site, <br />throughout the mining area, and two neazby wells. The first 25 piezometers were installed in the <br />' summer of 1994; two other piezometers were installed in late 1995, and the remainder were installed <br />in late 1996. Water levels were measured in each piezometer on a monthly basis. The average water <br />' level for all of the piezometers tvas calculated and a annual hydrograph was generated which shows <br />typical fluctuations throughout the year. <br />Figure 3 presents the typical annual water level hydrograph at the site, in graphica. and tabular <br />' format. The values shown represent the average depth to water below the ground surface at the <br />piezometer. As the data show, the average water level in the alluvium fluctuates between roughly <br />' four and six feet below the surface, or an average fluctuation of about two feet. Water levels begin <br />to increase in April or May, and remain high until July or August, at which time the water levels <br />begin to drop to a low point in late winter before the increases start again. <br />1 The increases in water level in the aquifer correspond to periods of recharge of the alluvium. <br />Com~ersely, the decreases in water level in the aquifer correspond to the periods of discharge from <br />the alluvium back to the stream system. The fluctuations are a result of recharge frorn the streams <br />' and tributary inflows, as well as from irrigation of the lands overlying the area to be mined. In this <br />analysis, and in order to conservatively look at the worst-case impacts of the mining operation on <br />' the alluvium-stream system, the entire fluctuation has been attributed to inflows from and outflows <br />to the streams. As a practical matter, some of this fluctuation is due to application. of irrigation <br />' water. When the imgation water rights are changed in water court, the impacts to the stream system <br />due to that portion of the water level fluctuations, will need to be mitigated. Therefore, a portion of <br />' the affects shown in this report will actually be mitigated in the fuhae through the water court change <br />case. <br />-2~- <br />i 1 1 /1i.~/or l(rq:rLn.l.;;o.uro ;. /rrr. <br />