2016-08-08_GENERAL DOCUMENTS - C1981019

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PR-04, Colowyo Coal Mine C1981-019 40 August 2016 change in the hydrologic balance is likely to occur. Furthermore, the area to be mined is a small fraction of watershed areas, and the general area will not be greatly affected. A discussion of the probable hydrologic consequences is found in Volume 15, Rule 2. 1. Potential Effects on Surface Water Quantity Based on the hydrologic balance calculations for the drainages in the general area and the fact that all runoff from the mine area is to be either diverted around the mine or retained in sedimentation ponds. Runoff in the permit area, which is diverted or detained, will continue to reach the historic drainages, and no change in the hydrologic balance is expected to occur. Since the area to be mined is a fraction of the total watershed areas, the general area will not be affected. The probable hydrologic consequences (PHC) section of the 1982 Findings Document predicted that there would be no significant effects to the hydrologic balance of Taylor, Wilson or Goodspring Creeks as a result of mining. Monitoring data in the mine's Annual Hydrology Reports (AHRs) to date confirms that there have been no significant impacts on water quantity of these streams due to mining operations at the Colowyo Mine. These reports provide some evidence that the Collom operations are also unlikely to impact the hydrologic balance. The following are anticipated hydrologic consequences to surface water quantity due to mining activities in the Collom area:  Natural springs near the pit might experience increased or decreased flow;  The pits, facilities pad, and spoil pile will eliminate several springs and seeps;  Hydraulic conductivity within the backfilled pits will be higher that the adjacent unmined area;  Peak flow in the West Fork of Jubb Creek may be reduced during mining. This will not, however, cause significant regional impacts. In the areas within and adjacent to the Colowyo Mine, the Division has found that the above- mentioned potential impacts to surface water quantity from activities in the Collom area are not likely significant. 2. Potential Effects on Surface Water Quality 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. This assertion was reiterated in the Colowyo PAP. Surface water monitoring data from Colowyo's monitoring program and observations by the Division have confirmed the prediction of no significant impacts to surface water quality to date. As noted for surface water quantity, these reports