2013-04-10_GENERAL DOCUMENTS - C1981019

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Information in the PAP and the 1982 Findings Document indicates that surface water quality in the general area is extremely variable. No adverse impacts from mining operations were projected and none have been observed to date. The Division's 1982 Findings Document predicted that no significant impacts on surface water quality in or adjacent to the permit area due to mining operations would occur. Water quality in and near the permit area is highly variable, changing in response to seasonal trends and precipitation events. Surface water monitoring data from the Operator's monitoring program and observations by the Division have confirmed the prediction of no significant impacts to surface water quality to date. The most significant potential impact to the hydrologic balance in the Collom Gulch area is the discharge of saline water from a spoil spring that may form and flow into the channel of Little Collom Gulch. Little Collom Gulch is an ephemeral drainage and had no measurable flow during baseline data collection. The most likely location for a spoil spring to develop in the Gulch is at the downdip end of the Collom Lite pit, in SE1 /4 Section 35, T4N, R94W. The operator predicts a spoil spring could develop at that location 58 years after the pit is backfilled. If such a spoil spring forms, it can be predicted to have an average discharge rate of 0.45 cfs and total dissolved solids content of approximately 3,000 mg /1. The operator predicts that if this spring forms, the spoil leachate will either evaporate or will be fully absorbed by the unsaturated valley fill of Little Collom Gulch, resulting in minimal impact to the ephemeral surface flows in the Gulch. The Division evaluates mining related impacts to river basins with Cumulative Hydrologic Impact Assessments (CHIA). The Yampa River CHIA was updated December 2011 to include potential discharges from the Collom expansion. The Yampa River CHIA is available for review at the Division offices. 3. Potential Effects on Ground Water The operator predicts that if a spoil spring develops at the toe of Collom Lite pit (as previously described in the discussion of surface water impacts), native ground water in the valley fill in Little Collom Gulch will dilute the spoil leachate and will result in no adverse impacts to the valley fill ground water. As an alternative to the predicted formation of a surface spoil spring at the toe of the Little Collom pit, the operator predicts all leachate in the backfilled pit could discharge into the unmined bedrock units of the Williams Fork Formation in the lowwall of the pit, resulting in no spoil spring on the land surface. The operator predicts migrating leachate in bedrock units will not adversely impact the hydrologic balance because there is minimal water saturation in the down gradient units. Colowyo Coal Mine C1981 -019 PR -03 48 April 10, 2013