2013-04-10_GENERAL DOCUMENTS - C1981019

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The operator explains that drawdown from pit dewatering in the Collom area will not adversely impact private water supply wells because those wells are beyond the predicted cone of depression of the pits. The proposed mining operations are not expected to adversely affect the water quality or quantity of the Trout Creek Sandstone in the Collom Gulch area because this unit is 400 feet beneath the mining sequence. Continued operations in the active pits from 1981 to present support the assertion that little water exists above the coal strata 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. The probability of aquifer cross - contamination is therefore negligible. The quality of ground water within the permit site has been rated poor by the USGS and designated for limited agricultural use only. The chemical composition of the area's 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 Colowyo Coal Mine C1981 -019 PR -03 49 April 10, 2013