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XIV. Protection of Underground Mining <br />The Division previously approved a variance to allow surface coal mining activities <br />to be conducted within 500 feet of an active or abandoned underground mine. The <br />Empire Mine extends underneath the west end of Trapper Mine. More than 800 feet <br />of vertical separation exists between Trapper's surface pit floors (now reclaimed) and <br />Empire's underground workings. Trapper will not be conducting any further mining <br />on the west end; the area has been fully reclaimed (4.19(1) and 4.22.4(1)). <br />XV. Subsidence Control <br />No specific approvals are granted to the applicant under this section. <br />XVI. Concurrent Surface and Underground Mining <br />No specific approvals are granted to the applicant under this section. <br />XVII. Operations on Alluvial Valley Frs <br />Operations on alluvial valley floors are discussed in Section 4.8.4 of Vol. IV of the <br />permit application. <br />Criteria for Alluvial Valley Floor Determination <br />Map M35A in the permit application shows that the following six drainages are the only <br />drainages in the vicinity of the Trapper Mine which contain unconsolidated stream-laid <br />holding streams: Yampa River, Williams Fork River, No Name Gulch, Johnson Gulch, <br />Pyeatt Gulch, and Flume Gulch. <br />Any of those alluvial valleys would meet the regulatory definition of an alluvial floor if <br />the valley has water availability sufficient for flood irrigation agricultural activities <br />[Section 1.04(10)] or has water availability sufficient for sub-irrigation agricultural <br />activities [Section 1.04(10)]. <br />Irrigation Agricultural Potential <br />Flood irrigation is practiced on the valley floors of the Yampa River in the Big Bottom <br />area and the Williams Fork River near its confluence with the Yampa. The four gulches <br />(No Name, Johnson, Pyeatt, and Flume) lack sufficient water availability for flood <br />irrigation. According to the Natural Resources Conservation Service, local irrigation <br />requires approximately 5 acre-feet of water per acre, after allowing for evaporation losses <br />(letter from Hill, 1980 referenced on page 2-539 of permit application). Summertime <br />evaporation in Moffat County exceeds precipitation by approximately 30 inches <br />(Evaporation from Lakes and Reservoirs by A.F. Meyer, 1942, Minnesota Resources <br />Commission, page 58). The largest annual water yield for any of the four gulches is <br />calculated to be the 225 acre-feet yield from Flume Gulch (page 2-412 of permit). This <br />amount of water would irrigate only 45 acres based on the 5 acre-feet of water per acre <br />Trapper Mine 35 September 21, 2009