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river influences results in a steep cone of depression that extends mostly to east. This drawdown would <br />likely affect the unlined Fulton Ditch and alluvial wells in the vicinity, depending on the saturated <br />thickness and the drawdown at the well. It is likely that the magnitude and extent of drawdown would <br />be of relatively short duration, since current mining plans call for the entire east cell to be mined out <br />during a single dry season. Upon completion of east cells mining, the "post-mining" situation discussed <br />below would apply. <br />Figures 7 and 8 provide contour maps of the simulated changes in water levels after mining for the wet <br />and dry seasons, respectively. The model simulations indicate that post-mining conditions are likely to <br />be similar to the pre-mining conditions. Two areas of note are just east of the mine property. East and <br />southeast of the slurry wall, the simulations indicate a water level drop of about 1 to 4 feet. This is due <br />to the realignment of the Bull Seep. East of the current Bull Seep, the surface and groundwater table <br />both rise. For hydraulic purposes, the bottom elevation of the Bull Seep must remain at its current <br />elevation after it is moved to the east. Hence, the Bull Seep intercepts the groundwater table further <br />east, acts as a drain for the area, and results in a simulated drawdown compared to current conditions. <br />This could impact the Fulton Ditch by increasing seepage losses if the ditch remained unlined. The other <br />simulated post-mine effect is a small amount of water mounding east of the former east cell. This is due <br />to the effects of a significantly lower hydraulic conductivity in the former east cell. Note that the post- <br />mining conditions apply after the east cell has been mined, since any activity within the main cell slurry <br />wall is practically separated from the rest of the alluvial aquifer. Figure 9 shows simulated groundwater <br />elevations after mining. In general, they are similar to the pre-mining elevation contours. <br />4.0 <br />A finite difference groundwater model was constructed for the proposed Hazeltine Mine. The model <br />indicates the groundwater near the mine will be lowered during mining in response to dewatering at the <br />east cell. Under a "worst case" scenario, drawdown (defined herein as two feet or more) was simulated <br />to extend over an area approximately 4,800 feet wide and 7,000 feet long during mining in the wet <br />season. During the dry season the magnitude of drawdown decreased (maximum of 44 feet instead of <br />47 feet) but the area of drawdown increased to 5,400 feet by 7,000 feet. However, as discussed in <br />Section 3, this effect will likely be of short duration since the entire east cell is scheduled to be mined in <br />a single dry season. After mining, a wet season drawdown of one to four feet was simulated in an <br />approximate 200-foot by 1,000-foot area immediately southeast of the slurry wall. In the simulation, <br />this drawdown was reduced to one-foot over an area 100-foot by 200-foot during the dry season. Also <br />during the wet season, a one foot drawdown was shown directly east of the slurry wall (400 foot by <br />1,500-foot). Water table mounding that might normally be expected on the upgradient side of the <br />Hazeltine slurry wall was simulated to be mitigated by the drain effect of the realigned Bull Seep. The <br />only area of simulated post-mining water table mounding (on the order of one foot) was simulated to <br />occur upgradient of the backfilled east cell. This mounding (one foot level) was simulated to extend a <br />maximum of approximately 900 feet (wet season) to 1,400 feet (dry season) to the east and southeast of <br />the property. <br />Due to the magnitude and extent of drawdown resulting from mining in the deepest portion of the east <br />cell, that portion of the area should be mined and backfilled as quickly as practicable. Dewatering and <br />mining in the rest of the east cell should result in less drawdown, particularly if mitigation ponds are <br />established near the mine edges. Impacts to domestic alluvial wells in the area of influence will depend <br />upon the depth of the well and the distance from the east cell. A groundwater mitigation plan should be <br />developed to specify plans for monitoring for potential adverse impacts to nearby alluvial domestic <br />wells and outline actions to mitigate these impacts if they occur. In general, if the dewatering draws <br />- 7 - July 2004 <br />I:U919 018\GW ModeNteponUiazdtinc_Rq_]_D.doc <br />