2005-01-03_REVISION - M1999120 (5)

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Ms. Lynn Mayer January 3, 2005 Page 2 cells and these water features. Therefore, the surface hydrology of these features will not be affected. Surface nmoff presently sheet-flows across the amendment area in a generally northeasterly direction. This sheet-flow concentrates in a Swale up against County Road 18 and either flows west to Little Dry Creek or east to the South Platte River. The amount of this sheet- flow is relatively small, and it does not sustain any wetlands or provide any other uses. Conversion of the amendment area to a water storage vessel, as proposed, will reduce this sheet-flow. However, the amount of sheet-flow is relatively small, it does not sustain any wetlands, nor is it used for any beneficial purpose. In summary, water will continue to be carried in Little Dry Creek and the East Lateral through and north of the amendment area. There will be no impact to major surface hydrologic features. Sheet-flow runoff from the site will be reduced once the area is mined, but only a small amount of runoff is generated and it does not support any wetlands or other beneficial uses. Therefore, the proposed amendment should have little or no negative affect on the prevailing surface water system. Groundwater LGE has been monitoring shallow groundwater depth in 14 monitoring wells located around the proposed amendment area, including upgradient and downgradient of the area. (The monitoring plan submitted to DMG shows 16 wells, but Wells 15 and 16 were damaged during slurry wall constmction). Groundwater levels have been measured monthly from May 2004 to the present. The slurry wall along the existing LGE operation was completed in April, so that the data are representative of conditions with the slun•y wall in place. Groundwater ranged from around less than 1 to approximately 11 feet below the ground in the area around the existing operation. Groundwater is shallower in monitoring wells located close to Little Dry Creek or imgation ditches. The range of depth to groundwater is consistent with that reported in studies by the U.S. Geological Survey (U5GS) and other available data. The direction of flow of groundwater is to the northeast. The monitoring data indicate "mounding" of groundwater on the upgradient side of the existing pit of 1 to 2 feet, and a "shadow" or lowering on the downgradient side of around 4 feet. The mounding effect dissipates relatively close to the pit; the shadow effect exists for around 1,400 feet north of the pit. Drawing 1 is a plot of average groundwater levels from the monitoring data. It should be noted that natural groundwater levels will fluctuate depending on several factors, including precipitation, imgation practices, flow in the river, time of year, etc. For example, groundwater dropped 4.07 feet in Well 9 from May through December 2004 while there were no operational changes at the existing LGE pit There have been no reported impacts on water wells from the existing pit in 2004. As subsequently discussed, few wells exist in the groundwater shadow.