Laserfiche WebLink
<br /> <br /> <br /> <br />PR-04, Colowyo Coal Mine C1981-019 41 August 2016 <br /> <br />provide some evidence that the Collom operations are also unlikely to disturb the hydrologic <br />balance. <br /> <br />The most significant potential impact to the hydrologic balance in the Collom area is the <br />discharge of saline water from a spoil spring that may form and flow into the channel of Little <br />Collom Gulch. The most likely location for a spoil spring to develop in the Collom Gulch is at <br />the down dip end of the Collom Pit. CCC predicts, and the Division concurs, that if this spring <br />forms, the spoil leachate will either evaporate or will be fully absorbed by the unsaturated valley <br />fill of Little Collom Gulch, resulting in minimal impact to the surface flows within the Collom <br />area or in adjacent areas. <br /> <br />The Division evaluates mining related impacts to river basins with Cumulative Hydrologic <br />Impact Assessments (CHIAs). The Yampa River CHIA was updated December 2011 to include <br />potential discharges from the Collom expansion. The Yampa River CHIA is available for review <br />at the Division offices. As noted earlier, the changes to the Collom project proposed with PR-04 <br />reduce the potential for impacts on the hydrologic balance on and adjacent to the Colowyo Mine <br />permit boundary (compared to the project proposed with PR-03), and the Division finds that the <br />operations proposed under the PR-04 application have been designed to prevent material damage <br />to the hydrologic balance outside the proposed permit area. <br /> <br /> <br /> <br />3. Potential Impacts to Groundwater Quantity and Quality <br /> <br />CCC will excavate the Collom pit to a depth below the water table, which necessitates that the <br />bedrock units within the pit footprint and its immediate vicinity be dewatered. This will be <br />achieved using 30-40 dewatering wells during the life of the mine. Wells will be drilled with a <br />spacing of 1000ft and will dewater the rock strata from below the Fab coal seam. Drawdown is <br />expected to be in the range of 40 to 250ft across the pit footprint, with the greatest depths in the <br />north. Based on a regional hydrogeologic model developed by Water Management Consultants <br />(WMC) in 2006, groundwater level drawdown from mine dewatering is anticipated to extend to <br />the south no farther than the drainage divide. To the east and west drawdown effects may extend <br />to or beyond the West Fork of Jubb Creek and Collom Creek respectively; a maximum <br />drawdown of 50ft is anticipated at these locations, the accuracy of the model prediction is limited <br />by uncertainty associated with the vertical hydraulic communication between the valley fill <br />aquifers and the underlying bedrock. Since regional flow is to the north, groundwater to the north <br />of the dewatered pit will tend to drain away from the pit. The water level will be monitored using <br />vibrating wire piezometers placed in monitoring holes. Monitoring holes will be drilled outside <br />the perimeter dewatering holes to the east and the west (500-1500ft from the pit). Monitoring <br />holes to the north will be adjacent to the pit. Monitoring to the south is not necessary. Water <br />pumped from the dewatering wells is expected to be pumped to a complex of five 200,000 gallon