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<br />southwestern boundary of the mine, some water level declines will occur between the nine and the <br />edge of the alluvial aquifer. Slight water level mounding may occur where the low permeability <br />barrier impedes the flow of ground water down the natural gradient; one such azea is northwest of <br />' the low permeability barrier on the northwestern boundary of the "Phase II" portion of the mine (see <br />Figure 1), In order to account for mounding in the model, which would be unrealistic with respect <br />' to ground surface elevations, a drain was included in the model along the upstream edge of the <br />barrier. This model drain prevented mounding from reaching unrealistic elevations with respect to <br />' the ground surface. <br />' The second mining simulation was representative of a worst-case scenario in which dewatering <br />occurs without the low permeability barrier installed. Again, the simulation was Lased on the <br />' assumption that the entire mine was dewatered simultaneously. To simulate this difference, the <br />hydraulic conductivity in the vicinity of the bamer was set equal to that of the aquifer as a whole. <br />' The water level elevations and drawdowns resulting from this simulation are presented in <br />Appendices T and U. This simulation indicated that without the barrier, drawdowns spread slightly <br />' ' further into the aquifer and could result in greater water level declines in the vicinity of the South <br />' Branch. <br />' Modeled water level changes during the two mining scenarios at the locations of each water supply <br />well are presented in Table 3. As presented in the table, water level declines in the vicinity of <br />' neighboring wells during mining range from a rise in water level to a decline of about '..29 feet. The <br />greatest water level declines occur in the vicinity of the Atkins well {well number 1 ] on Figure 2), <br />' where the water level may decline on the order of 1.29 feet during mining. Water le gel impacts to <br />this well were classified as moderate risk. Water level declines are relatively high in this area <br />' because the well location is within the mine permit area and is located in close prozim.ry to the mine <br />boundary and directly down-gradient of a planned lined pit. Drawdowns in additional wells will be <br />less than one foot (low risk), although there may be some minor changes in water level. Table 3 <br />presents risk level classifications for each of the wells. The Atkins well was the only well classified <br />' as moderate risk; all other wells were classified as low or zero risk. There were no wells classified <br />' -18- <br />' ' lli.,hop-lfm,;Arn :Itsnriorrc, hip. <br />