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drainage. Wetlands plants (cattails) are growing in the lower end of Flume Gulch within <br />the channel area, but the wetlands preclude the potential for sub-irrigation agricultural <br />activities. A Division representative also inspected parts of Pyeatt, Johnson, and No <br />Name drainages. Agricultural species types and productivity appeared uniform across <br />those drainages. <br /> <br /> Alluvial Valley Floor Determination <br /> <br />Based on the presence of unconsolidated stream-laid holding streams and the presence of <br />water availability sufficient for flood irrigation agricultural activities, the following two <br />alluvial valleys have been determined to be alluvial valley floors: the Yampa River in the <br />Big Bottom area and the Williams Fork River near its confluence with the Yampa River. <br /> <br />The four gulches (No Name, Johnson, Pyeatt, and Flume) are determined to not be <br />alluvial valley floors based on their absence of water availability sufficient for irrigation <br />or sub-irrigation agricultural activities. (This determination applies, as well, to the <br />approximate 20-acre area in the upper part of Flume Gulch previously determined to be <br />an AVF. In addition, that area lacks a stream channel meeting the minimum size criteria <br />of greater than 3 feet in bank full width and greater than 0.5 feet in bank full depth <br />\[Section 1.04(142)\]; and therefore, that area does not contain an unconsolidated stream- <br />laid holding stream.) (2.06.8(3)(c)) <br /> <br />Prior to the disturbance within the PR7 expansion area, Trapper will need to evaluate if <br />AVFs exist within the expansion area and provide the information required by Rule <br />2.06.8 if necessary. The Division has stipulated the approval of PR7 to this effect (see <br />Stipulation No. 22 above). <br /> <br /> Impacts to Alluvial Valley Floors <br /> <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 <br />(surface and ground water) from the proposed mine area. The majority of the flow in the <br />river and subsequent recharge to the alluvial aquifer comes from the headwaters portions <br />of the drainage, far upstream from the Trapper Mine. The applicant states that the <br />contribution of surface water from the Trapper Mine is insignificant and is estimated at <br />2 <br />0.07cfs/mi (page 2-533 of permit application). Also, the ground water contribution to <br /> <br />the base flow of the Yampa River is so small that it is undetectable. This is substantiated <br />by seepage, runoff, and potentiometric studies in Appendix H of the permit application <br />which show that: 1) The Yampa River loses surface water flow to the alluvial aquifer as <br />it flows past the mine area, and 2) the Yampa River alluvial aquifer is hydraulically <br />isolated from the bedrock aquifers of the Williams Fork Formation. In addition, all <br />disturbance related to the mine is located at least one mile from the southern boundary of <br />the Yampa River AVF. Based on the information presented by the applicant, the <br />Division finds that the proposed surface coal mining operation will not interrupt, <br />discontinue, or preclude farming on the Yampa River AVF, and will not materially <br />damage the quantity or quality of water in surface or ground water systems that supply <br />the Yampa River AVF. (4.24.3(1)), (4.24.3(3), and 2.06.8(5)(a)(ii)) <br /> <br /> <br />41 <br /> <br />Trapper MineJuly 9, 2013 <br /> <br />