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permit area. <br />During the Permit Revision No. 2 (PR-02) review, the Division further evaluated potential impacts to <br />groundwater within and adjacent to the permit area and with regard to establishing groundwater <br />points of compliance. Three specific zones of groundwater that have the potential to be impacted <br />were evaluated. These include bedrock groundwater, backfill and excess spoil groundwater, and <br />alluvial groundwater. A synopsis of our review is provided below. <br />Bedrock Groundwater <br />The upper bedrock units of the strata to be mined demonstrate relatively low yields, and groundwater <br />occurrences are not continuous but are a series of perched systems. The perched aquifers aze of <br />limited extent and largely removed by the mining process. Drill holes within the Colowyo Permit <br />area to the lowest coal seam to be mined were generally dry and any water produced from zones <br />containing coal deposits is known to be of poor quality. <br />The Trout Creek Sandstone is an aquifer of regional extent and underlies most of the mining impact <br />areas. The potential impact from mining activities to the Trout Creek Sandstone is limited. The <br />Trout Creek Sandstone in under confined conditions. The Trout Creek Sandstone aquifer is <br />separated from the lowest coal seam to be mined by approximately 590 feet in south Taylor. Units <br />below the lowest coal seam to be mined consist of sandstones, shales, and coals. The shale units <br />have low permeability and may be a barrier to subsurface migration of leachate. As indicated in the <br />updated PHC for PR-02, about 165 feet above the Trout Creek Sandstone is atwo-foot thick smectite <br />clay layer (Km) that is laterally extensive through the area. This layer has been found to be of low <br />permeability and is an additional impediment to downward groundwater flow. According to the <br />revised PHC drilling by Colowyo between 1995 and 2005 has found that no significant water is <br />encountered in the South Taylor pit until drilling proceeds below the Km bed. For these reasons <br />described above, it is unlikely that the Colowyo operation will impact the Trout Creek Sandstone. <br />It is the belief of the Division that coal mining operations at Colowyo do not have the potential to <br />negatively impact bedrock groundwater, and that no point of compliance need be established for <br />bedrock groundwater. <br />Based on the review of the groundwater at the Colowyo Mine, one new stipulation is being added to <br />the permit: <br />STIPULATION 7 <br />THE COLOWYO COAL COMPANY SHALL SUBMIT A TECHNICAL REVISION TO THE <br />DIVISION WHICH PROVIDES AN ANALYSIS OF GROUNDWATER POINTS OF <br />COMPLIANCE AT THE COLOWYO MINE PURSUANT TO RULE 4.05.13(1). THIS <br />ANALYSIS WILL BE DONE 1N CONSULTATION WITH THE DIVISION AND WILL <br />Proposed Decision and Findings of Compliance 4 May 2007 <br />Perini[ Revision 02 Page 41 <br />