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State Req. <br />Yampa River. The alluvial deposits contained within and adjacent to the <br />Seneca II permit will be covered in greater detail in the site specific <br />portion of this section, and in the section on alluvial valley floors. <br />Topography and geologic structure also play an important part in under- <br />standing the regional hydrogeology near the Seneca II permit. As a <br />general rule, topography closely conforms to structural gradients for the <br />middle coal-bearing Williams Fork Formation rocks. Dip slopes, such as <br />those found at The Seneca II permit, are common features throughout the <br />Twentymile Park area. It is important to closely examine the hydro- <br />geology of these areas because these dip slopes contain the largest <br />portion of local coal reserves extractable by surface mining methods. <br />Exhibit 6-12 shows the major structural features of the area in relation <br />to the Seneca II permit. These structures appear to control the overall <br />lateral movement of ground water in the region. Ground water generally <br />moves downdip from recharge areas located on topographic and structur- <br />al highs (anticlines) to discharge areas located in structural lows ~syn- • <br />clines) and alluvium. Thus water entering recharge areas on the west <br />flank of the Tow Creek Anticline will move westward and northwestward <br />along the plunging axis of tfie Hayden Syncline. Some of this ground <br />water will be discharged into the Little Grassy Creek alluvium and will <br />exit the permit area as surface water flow. Ground water flow on the <br />southeast flank of the anticline will initially move south and.southeast- <br />ward into the Twentymile Park Syncline and then will flow primarily <br />westward and northwestward into the Hayden Syncline across the struc- <br />tural divide separating these two synclines. A small component of <br />ground water flow from the southeast flank may move northward and <br />eventually discharge into the Yampa River. Another possible avenue for <br />ground water discharge in the region is a series of normal faults which <br />exist to the north and south of the permit area. The dry condition of <br />faults encountered during mining in the northern part of the permit area <br />indicate, however, that faults probably act as barriers rather than con- <br />duits for ground water flow. <br />7-4 <br />Revised 5/27/81 <br />• <br />