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Twentymile Coal, LLC (TC) <br />Narrative <br />Lease by Modification Application Wolf Creek Reserve — April 2014 <br />in gradient, as the velocity of the water diminishes as it passes through the ponded areas with <br />resultant sediment loss, and gradual adjustment of the stream to a dynamic equilibrium. <br />Fish Creek Alluvial Valley Floor - The planned mining sequence will result in surface <br />subsidence effects to Fish Creek and associated Alluvial Valley Floor (AVF) areas, as well as <br />various stock ponds. The identified AVF areas are located over a portion of the Wolf Creek <br />mining area, however, TC has already successfully undermined these areas without <br />significant impact on the essential hydrologic function. <br />There are no known irrigation head -gates located within the proposed mining area, indicating <br />that flood -irrigation of these bottom lands has not previously occurred and is probably not <br />practical, and that any enhancement of vegetative growth in the AVF areas probably results <br />from sub -irrigation. Subsiding portions of the AVF will tend to increase the potential for <br />sub -irrigation to occur by lowering the stream base level and adjacent terrain relative to <br />normal seasonal flow levels. <br />In addition to the minor ponding that will result from subsidence of the AVF, there will be <br />areas within the AVF where the water level will be immediately below the surface, i.e. <br />saturated soil conditions. These effects will generally be limited to low areas adjacent to the <br />Fish Creek stream channel. The overall effect may be localized changes in vegetation, with <br />water -tolerant species taking over areas of saturated soils, and resultant increases in the size <br />and extent of the riparian vegetation communities, which is considered a positive impact. <br />E. Geological, Cultural, and Archeological Features — Wolf Creek Reserve <br />Geology <br />The regional geology of the proposed lease modification tract is described in detail in TC's <br />Mining and Reclamation Permit (CDRMS Permit No. C-82-056, Rule 2.04.6). The following <br />information from the Permit is incorporated into this application by reference. <br />TC's current mining operation, the Foidel Creek Mine, is located at the southeast tip of the <br />Yampa Coal Field of the Green River Region. The Yampa Coal Field is a synclinal extension <br />of the Washakie -Sand -Wash structural basin located in northwestern Colorado and south-central <br />Wyoming. The main axis of the basin is highly modified by numerous smaller anticlines, <br />synclines, and faults. The boundary of the Yampa Coal Field is defined to the southwest by the <br />Axial Basin Anticline, and to the east by the Park Range Uplift. The Permit Area is within <br />Twentymile Park, a structural and topographic basin located immediately north of the reclaimed <br />CYCC surface mine in Routt County. The basin is underlain by a large, high-quality coal <br />reserve, which is mineable in many areas by underground methods. The geology and prominent <br />structural features are illustrated on Figure 3. <br />Strata in Twentymile Park have been subjected to progressive structural deformation, which can <br />be separated into two major events. The first event formed large folds and reverse faults, while <br />the second event formed normal faults. Three large asymmetrical folds, the Oak Creek, Tow <br />WCR BLM Lease App Narrative 0414.docx Page 4 <br />