2013-07-09_REVISION - C1981010 (7)

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The four gulches (No Name, Johnson, Pyeatt, and Flume) are determined to not be alluvial valley floors based on their absence of water availability sufficient for irrigation or sub - irrigation agricultural activities. (This determination applies, as well, to the approximate 20 -acre area in the upper part of Flume Gulch previously determined to be an AVF. In addition, that area lacks a stream channel meeting the minimum size criteria of greater than 3 feet in bank full width and greater than 0.5 feet in bank full depth [Section 1.04(142)]; and therefore, that area does not contain an unconsolidated stream - laid holding stream.) (2.06.8(3)(c)) IMDacts to Alluvial Vallev Floors The potential for the proposed mining operation to impact the Yampa River AVF is negligible. Generally, the Yampa River AVF receives very little of its water supply (surface and ground water) from the proposed mine area. The majority of the flow in the river and subsequent recharge to the alluvial aquifer comes from the headwaters portions of the drainage, far upstream from Trapper. The applicant states that the contribution of surface water from the Trapper mine is insignificant and is estimated at 0.07cfs /mi 2 (page 2 -533 of permit application). Also, the ground water contribution to the base flow of the Yampa River is so small that it is undetectable. This is substantiated by seepage, runoff, and potentiometric studies in Appendix H of the permit application which show that: 1) The Yampa River loses surface water flow to the alluvial aquifer as it flows past the mine area, and 2) the Yampa River alluvial aquifer is hydraulically isolated from the bedrock aquifers of the Williams Fork Formation. In addition, all disturbance related to the mine is located at least one mile from the southern boundary of the Yampa River AVF. Based on the information presented by the applicant, the Division finds that the proposed surface coal mining operation will not interrupt, discontinue, or preclude farming on the Yampa River AVF, and will not materially damage the quantity or quality of water in surface or ground water systems that supply the Yampa River AVF. (4.24.3(1)), (4.24.3(3), and 2.06.8(5)(a)(ii)) The potential for impacts from mining to the Williams Fork AVF is also negligible. The Williams Fork River is located south of the proposed mining area. Disturbed areas in the permit area which drain to the Williams Fork River are located in Elk, Ute, and Deer drainages; these are relatively small drainages of less than 30 acres each. Surface discharge from the sediment ponds in these drainages is limited to spring snowmelt almost exclusively. Discharges from the ponds flow down ephemeral channels which cross an outcrop of the permeable Twentymile Sandstone that is a few hundred feet wide. It is likely that much of the discharge from the ponds infiltrate into this outcrop prior to reaching the Williams Fork River. The Twentymile Sandstone dips northward, away from the Williams Fork River and underneath the Trapper Mine; consequently, the pond discharges that infiltrate into the sandstone flow away from the Williams Fork River as ground water. The potential for contaminating ground water in the Twentymile Sandstone is negligible due to the relatively small volume of water from the ponds compared to the large volume of ground water in the Twentymile Sandstone. Water from the ponds would also be subject to large evaporation losses on this scrubby, south - facing slope. Trapper Mine 35 July 9, 2013