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The proposed mining operations aze not expected to decrease the water quality or quantity of the <br />Trout Creek aquifer. Since the Trout Creek Sandstone member underlies the deepest coal seam to be <br />mined by 800 feet, it is estimated that Colowyo's operations should not impact this aquifer in any <br />manner. <br />Underlying the Iles Formation is the Mancos Shale, a unit 5,000 feet thick, consisting of marine <br />shales and limestones. This unit is impermeable and creates the confining base for the Trout Creek <br />Sandstone aquifer. <br />Continued operations in the active pits from 1981 to present support the assertion that little water <br />exists above the coal stratum to be mined. What water does exist has only been experienced under <br />perched conditions. Seeps encountered during operations have been consumed by the face or <br />evaporated from the floor of the pit. Excavation to the lower coal seams has produced dry conditions, <br />indicating there is no lateral or vertical continuity in the connection between the Iles and the <br />Williams Fork Formations; so the probability of aquifer cross- contamination is negligible. <br />The quality of ground water within the permit site has been rated poor by the USGS and designated <br />for limited agricultural use only. The chemical composition of the area's water was tested by the <br />USGS in 1978 and found to be somewhat saline, alkaline and hard (see pages 2.04.7-12 and 13 in the <br />Permit and Table 1). pH varies from 7.2 to 8.4. The USGS report indicates that concentrations of <br />trace metals razely exceed health limits. Specific conductivity averages 1440-1390 mmhos with a <br />range between 720 and 2700 mmhos, exceeding Environmental Protection Agency (EPA) secondary <br />drinking water standazds (see permit pages 2.04.7-14 through 18 and Table 2). The above factors, <br />coupled with low selenium levels ranging from 0.001 to 0.002, allow the water to be used for stock <br />watering. <br />An EPA report entitled "Environmental Effects of Western Coal Mining, Part III" suggested that the <br />alkaline nature of western water (including that within this permit azea) may limit or reduce the <br />solubility of heavy metals concentration in waters near or adjacent to a coal mining operation. This <br />fact, together with a low coal sulfur content (0.33 to 0.57 percent), more than likely accounts for the <br />low trace metals found in the somewhat alkaline ground water on the permit site. <br />In conclusion, impacts of the Colowyo surface mining operations on bedrock aquifers aze confined to <br />the permit area and are not expected to be significant. <br />A slight potential for degradation of alluvial ground water was recognized in the Permit and the 1982 <br />Findings Document. A plan was approved to monitor alluvial ground water on Goodspring and <br />Wilson Creek. Results of monitoring indicate no detectable impacts on alluvial ground water to date. <br />Pursuant to Rule 2.07.6(2)(c), the assessment of the probable consequences of the proposed mining <br />operation and the assessment of the probable cumulative impact of all anticipated mining in the azea <br />on the hydrologic balance, as described in Rule 2.05.6(3), have been made. The proposed operation <br />has been found to be designed to prevent material damage to the hydrologic balance outside the <br />Proposed Decision and Findings of Compliance 4 May 2007 <br />Permit Revision 02 Page 40 <br />