2009-09-14_REVISION - C1981019 - Laserfiche WebLink

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Underlying the Iles Formation is the Mancos Shale, a unit 5,000 feet thick, consisting of marine shales and limestones. This unit is impermeable and creates the confining base for the Trout Creek Sandstone aquifer. Continued operations in the active pits from 1981 to present support the assertion that little water exists above the coal stratum to be mined. What water does exist has only been experienced under perched conditions. Seeps encountered during operations have been consumed by the face or evaporated from the floor of the pit. Excavation to the lower coal seams has produced dry conditions, indicating there is no lateral or vertical continuity in the connection between the Iles and the Williams Fork Formations; so the probability of aquifer cross- contamination is negligible. The quality of ground water within the permit site has been rated poor by the USGS and desi?-a-L u Wr iiiiitcu a6llcui?urai use only. Tile c?ienlical COMPOSition of die areas water was tested by the USGS in 1978 and found to be somewhat saline, alkaline and hard (see pages 2.04.7-12 and 13 in the Permit and Table 1). pH varies from 7.2 to 8.4. The USGS report indicates that concentrations of trace metals rarely exceed health limits. Specific conductivity averages 1440-1390 mmhos with a range between 720 and 2700 mmhos, exceeding Environmental Protection Agency (EPA) secondary drinking water standards (see permit pages 2.04.7-14 through 18 and Table 2). The above factors, coupled with low selenium levels ranging from 0.001 to 0.002, allow the water to be used for stock watering. An EPA report entitled "Environmental Effects of Western Coal Mining, Part III" suggested that the alkaline nature of western water (including that within this permit area) may limit or reduce the solubility of heavy metals concentration in waters near or adjacent to a coal mining operation. This fact, together with a low coal sulfur content (0.33 to 0.57 percent), more than likely accounts for the low trace metals found in the somewhat alkaline ground water on the permit site. In conclusion, impacts of the Colowyo surface mining operations on bedrock aquifers are confined to the permit area and are not expected to be significant. A slight potential for degradation of alluvial ground water was recognized in the Permit and the 1982 Findings Document. A plan was approved to monitor alluvial ground water on Goodspring and Wilson Creek. Results of monitoring indicate no detectable impacts on alluvial ground water to date. Pursuant to Rule 2.07.6(2)(c), the assessment of the probable consequences of the proposed mining operation and the assessment of the probable cumulative impact of all anticipated mining in the area on the hydrologic balance, as described in Rule 2.05.6(3), have been made. The proposed operation has been found to be designed to prevent material damage to the hydrologic balance outside the permit area. Proposed Decision and Findings of Compliance 14 September 2009 Permit Renewal 05 Page 43