2009-09-14_REVISION - C1981019 - Laserfiche WebLink

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During the Permit Revision No. 2 (PR-02) review, the Division further evaluated potential impacts to groundwater within and adjacent to the permit area and with regard to establishing groundwater points of compliance. Three specific zones of groundwater that have the potential to be impacted were evaluated. These include bedrock groundwater, backfill and excess spoil groundwater, and alluvial groundwater. A synopsis of the Division's review is provided below. Bedrock Groundwater The upper bedrock units of the strata to be mined demonstrate relatively low yields, and groundwater occurrences are not continuous but are a series of perched systems. The perched aquifers are of limited extent and largely removed by the mining process. Drill holes within the Colowyo Permit area to the lowest coal seam to be mined were generally dry and any water produced from zones containing coal deposits is known to be of poor quality. The Trout Creek Sandstone is an aquifer of regional extent and underlies most of the mining impact areas. The potential impact from mining activities to the Trout Creek Sandstone is limited. The Trout Creek Sandstone in under confined conditions. The Trout Creek Sandstone aquifer is separated from the lowest coal seam to be mined by approximately 590 feet in south Taylor. Units below the lowest coal seam to be mined consist of sandstones, shales, and coals. The shale units have low permeability and may be a barrier to subsurface migration of leachate. As indicated in the updated PHC for PR-02, about 165 feet above the Trout Creek Sandstone is a two-foot thick smectite clay layer (Km) that is laterally extensive through the area. This layer has been found to be of low permeability and is an additional impediment to downward groundwater flow. According to the revised PHC drilling by Colowyo between 1995 and 2005 has found that no significant water is encountered in the South Taylor pit until drilling proceeds below the Km bed. For these reasons described above, it is unlikely that the Colowyo operation will impact the Trout Creek Sandstone. It is the belief of the Division that coal mining operations at Colowyo do not have the potential to negatively impact bedrock groundwater, and that no point of compliance need be established for bedrock groundwater. Based on the review of the groundwater at the Colowyo Mine, the following stipulation was added to the permit as a part of the Permit Revision 02 review process: STIPULATION 7 THE COLOWYO COAL COMPANY SHALL SUBMIT A TECHNICAL REVISION TO THE DIVISION WHICH PROVIDES AN ANALYSIS OF GROUNDWATER POINTS OF COMPLIANCE AT THE COLOWYO MINE PURSUANT TO RULE 4.05.13(1). THIS ANALYSIS WILL BE DONE IN CONSULTATION WITH THE DIVISION AND WILL INCLUDE A WRITTEN DETERMINATION OF THE NEED FOR GROUNDWATER POINTS OF COMPLIANCE AT THE MINE. IF DEEMED APPROPRIATE, BASED ON THIS ANALYSIS, COLOWYO SHALL ESTABLISH ONE OR MORE POINTS OF Proposed Decision and Findings of Compliance 14 September 2009 Permit Renewal 05 Page 44