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• <br />-4- <br />create and maintain a permanent "pond" between Sta. 0 +00 and approximately <br />Sta. 4 +50. West of Sta. 0 +00, the floor of the pit - istotally submerged. <br />Figure 2 presents the approximate extent of seeps observed and ground water <br />impounded at the time of our field investigation. From conversations with <br />personnel of Colorado Yampa Coal, we understand that during spring runoff <br />and after periods of intense rainfall, very little water runs off the spoil <br />surface above the pit, but at a later time appears to manifest itself <br />as numerous springs or seeps at the base of the spoil. <br />PROPOSED DEVELOPMENT <br />Several underground mine entires are to be constructed in the bottom of <br />the vacated pit. The mine will initially be operated on an experimental <br />• basis using three entries installed between Sta. 0 +00 and Sta. 4 +50. Ex- <br />perimental operations are expected to last between 3 and 5 years. A full -scale <br />operation will be developed if it is proved to be economically attractive. <br />A total of about 20 entries may be constructed for the full -scale operation <br />utilizing the entire pit from Sta. 0 +00 to Sta. 17 +00 ±. <br />We understand that a 200 -foot wide pit floor will be necessary for the <br />operation. Three alternatives for widening the pit floor have been considered: <br />(1) move the existing highwall to the north about 150 feet and grade the face <br />of the spoil as necessary for stability, (2) move the! spoil to the south about <br />150 feet and flatten the highwall as necessary for stability, or (3) rave <br />both the highwall and spoil about 75 feet each. Consideration is also being <br />given to sloping the pit floor downward from the bottom of the highwall to <br />the spoil toe at about 5 percent to provide surface drainage away from mine <br />• <br />