2009-05-22_GENERAL DOCUMENTS - C1981044

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valley floor is the capacity for flood irrigation, coinciding with the regional practice. Subirrigation may also occur, but it is considered secondary to flood irrigation. The No. 5 Mine and associated facilities were established on the Williams Fork River valley floor during the early 1970s. Mine entries were developed into the F coal seam, which outcropped above the valley floor. All surface facilities were constructed near the portal entries on the valley floor. The No. 5 and 6 Mines utilize the original portal entries and surface facilities as well as the surface facilities added to the Empire Energy operation during 1981 and 1982. The No. 5 Mine mains extend across the Williams Fork alluvial valley floor. The mains of the No. 6 Mine, which are developed in the underlying E Seam, will directly underlie the No. 5 Mine mains. Subsidence monitoring to date has shown no impacts to the alluvial valley floor due to the development mining underneath the Williams Fork alluvial valley floor. Technical Revision No. 19 was submitted May 6, 1991, proposing to conduct extraction mining beneath the Williams Fork alluvial valley floor and State Highway 13. The Division approved construction of development mains only and additional subsidence monitoring along Highway 13. Upon cessation of mining, the pumps which drain the mine of water will be shut off and the mine workings allowed to fill. In the Probable Hydrologic Consequences section of the permit application, the applicant has projected impacts that could occur to the Williams Fork alluvial water quality due to seepage from the flooded mine workings into the Williams Fork alluvium. This scenario assumes that the coal seams are in direct hydrologic communication with the alluvium of the Williams Fork River. Upon flooding of the mines, a head is expected to occur which would allow recharge of the alluvium by the mine water. The mine water presently pumped from the No. 5 Mine is high in sodium content. Using Darcy's Law, the applicant has projected a net impact of the seepage into the alluvial valley floor to increase the SAR level from 1.9 to 5.2. Although the SAR is projected to increase significantly, the level is still below that considered hazardous to crop development. The increased SAR would impact alluvial water in contact with the coal seams, specifically water available through subirrigation. The essential hydrologic function of this AVF is flood irrigation, as supplied by the surface water of the Williams Fork River. As the Williams Fork stream water is not projected to be significantly impacted by the mining operation, the essential function of flood irrigation will not be impaired. This essential hydrologic function, flood irrigation, will be reestablished upon completion of reclamation activities. The surface facilities will be removed, topsoil replaced, and the site seeded with the rangeland or the pastureland mixture, where applicable. The pasturelands will then be flood irrigated. The rangeland and marshy areas will not be irrigated. Yampa River Alluvial Valley Floors The Eagle No. 9 Mine has undermined portions of the Big Bottom alluvial valley floor (AVF). The Eagle No. 5 Mine has mined in areas beneath or hydrologically adjacent to two alluvial valley floors (AVF's) along the Yampa River; the Big Bottom and the Eagle Mine Complex 37 Pernit Renewal 05 C-1981-044 May 22, 2009