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the portal entries on the valley floor. The No. 5 and 6 Mines utilize the original portal <br />entries and surface facilities as well as the surface facilities added to the Empire Energy <br />operation during 1981 and 1982. The No. 5 Mine mains extend across the Williams <br />Fork alluvial valley floor. The mains of the No. 6 Mine, which are developed in the <br />underlying E Seam, will directly underlie the No. 5 Mine mains. Subsidence monitoring <br />to date has shown no impacts to the alluvial valley floor due to the development mining <br />underneath the Williams Fork alluvial valley floor. <br />Technical Revision No. 19 was submitted May 6, 1991, proposing to conduct extraction <br />mining beneath the Williams Fork alluvial valley floor and State Highway 13. The <br />Division approved construction of development mains only and additional subsidence <br />monitoring along Highway 13. <br />Upon cessation of mining, the pumps which drain the mine of water will be shut off and <br />the mine workings allowed to fill. In the Probable Hydrologic Consequences section of <br />the permit application, the applicant has projected impacts that could occur to the <br />Williams Fork alluvial water quality due to seepage from the flooded mine workings <br />into the Williams Fork alluvium. This scenario assumes that the coal seams are in direct <br />hydrologic communication with the alluvium of the Williams Fork River. Upon <br />flooding of the mines, a head is expected to occur which would allow recharge of the <br />alluvium by the mine water. The mine water from the No. 5 Mine is high in sodium <br />content. The applicant has projected a net impact of the seepage into the alluvial valley <br />floor to increase the SAR level from 3.6 to 9.4. The increased SAR would impact <br />alluvial water in contact with the coal seams, specifically water available through <br />subirrigation. The essential hydrologic function of this AVF is flood irrigation, as <br />supplied by the surface water of the Williams Fork River. As the Williams Fork stream <br />water is not projected to be significantly impacted by the mining operation, the essential <br />function of flood irrigation will not be impaired. <br />This essential hydrologic function, flood irrigation, will be reestablished upon <br />completion of reclamation activities. The surface facilities will be removed, topsoil <br />replaced, and the site seeded with the rangeland or the pastureland mixture, where <br />applicable. The pasturelands will then be flood irrigated. The rangeland and marshy <br />areas will not be irrigated. <br />Yampa River Alluvial Valley Floors <br />The No. 9 Mine has undermined portions of the Big Bottom alluvial valley floor (AVF). <br />The No. 5 Mine has mined in areas beneath or hydrologically adjacent to two alluvial <br />valley floors (AVF's) along the Yampa River: the Big Bottom and the Round Bottom <br />alluvial valley floors. Each of these alluvial valley floors are discussed separately, <br />along with the potential impacts of mining. <br />Yampa River Big Bottom Alluvial Valley Floor <br />The approximate boundary of the Big Bottom AVF is shown on Map 25 of the permit <br />application. Hayfields and pastureland are located in the Big Bottom (AVF) area and <br />are flood irrigated. <br />Williams Fork Mines 38 Permit Renewal 06 <br />C- 1981 -044 December 8, 2014 <br />