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irrigation agricultural activities. (This determination applies, as well, to the approximate 20- <br />acre area in the upper part of Flume Gulch previously determined to be an AVF. In addition, <br />that area lacks a stream channel meeting the minimum size criteria of greater than 3 feet in <br />bank full width and greater than 0.5 feet in bank full depth [Section 1.04(142)]; and <br />therefore, that area does not contain an unconsolidated stream-laid holding stream.) <br />(2.06.8(3)(c)) <br />Impacts to Alluvial Valley Floors <br />The potential for the proposed mining operation to impact the Yampa River AVF is <br />negligible. Generally, the Yampa River AVF receives very little of its water supply (surface <br />and ground water) from the proposed mine area. The majority of the flow in the river and <br />subsequent recharge to the alluvial aquifer comes from the headwaters portions of the <br />drainage, far upstream from Trapper. The applicant states that the contribution of surface <br />water from the Trapper mine is insignificant and is estimated at 0.07cfs/mi2 (page 2-533 of <br />permit application). Also, the ground water contribution to the base flow of the Yampa <br />River is so small that it is undetectable. This is substantiated by seepage, runoff, and <br />potentiometric studies in appendix H of the permit application which show that: 1) The <br />Yampa River loses surface water flow to the alluvial aquifer as it flows past the mine area, <br />and 2) the Yampa River alluvial aquifer is hydraulically isolated from the bedrock aquifers <br />of the Williams Fork Formation. In addition, all disturbance related to the mine is located at <br />least one mile from the southern boundary of the Yampa River AVF. Based on the <br />information presented by the applicant, the Division finds that the proposed surface coal <br />mining operation will not interrupt, discontinue, or preclude farming on the Yampa River <br />AVF, and will not materially damage the quantity or quality of water in surface or ground <br />water systems that supply the Yampa River AVF. (4.24.3(1)), (4.24.3(3), and <br />2.06.8(5)(a)(ii)) <br />The potential for impacts from mining to the Williams Fork AVF is also negligible. The <br />Williams Fork River is located south of the proposed mining area. Disturbed areas in the <br />permit area which drain to the Williams Fork River are located in Elk, Ute, and Deer <br />drainages; these are relatively small drainages of less than 30 acres each. Surface discharge <br />from the sediment ponds in these drainages is limited to spring snowmelt almost exclusively. <br />Discharges from the ponds flow down ephemeral channels which cross an outcrop of the <br />permeable Twentymile Sandstone that is a few hundred feet wide. It is likely that much of <br />the discharge from the ponds infiltrate into this outcrop prior to reaching the Williams Fork <br />River. <br />The Twentymile Sandstone dips northward, away from the Williams Fork River and <br />underneath the Trapper Mine; consequently, the pond discharges that infiltrate into the <br />sandstone flow away from the Williams Fork River as ground water. The potential for <br />contaminating ground water in the Twentymile Sandstone is negligible due to the relatively <br />small volume of water from the ponds compared to the large volume of ground water in the <br />Twentymile Sandstone. Water from the ponds would also be subject to large evaporation <br />losses on this scrubby, south-facing slope. <br />Trapper Mine 31 July 25, 2008