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to be mined during the initial years of production. Predictions of probable <br />disruption of the hydrologic regime from subsidence were based on an <br />analysis of those data. WFU originally predicted that tension cracks from <br />subsidence may develop in formations directly underlying Red Wash and that <br />these cracks may extend upward for several tens of feet (oral communication <br />with experts in this field; Page II. C-106b of the permit application). These <br />cracks were predicted to be of limited extent; therefore, a minimal amount of <br />surface water was predicted to be siphoned into them. Furthermore, WFU <br />predicted that sediment accumulating in the cracks, and clays in the <br />overburden would ultimately seal them off from surface inflow. <br />Continued monitoring of Red Wasfi has confumed WFU's predictions. As <br />projected, subsidence in Red Wash initially resulted in water ponding in the <br />stream bottom. The high content of silt and clay carried by Red Wash rapidly <br />fills the ponds. The silt and clay layers have sealed any cracks that formed in <br />the alluvium as the result of subsidence. Water continues to flow in the <br />surface channel at Red Wash while piezometric levels in the basal alluvial <br />gravel have dropped, indicating that the basal alluvium is not recharged by <br />surface flow infiltration. <br />Impacts on Scullion Gulch are expected to be similar to those on Red Wash, <br />although maximum vertical movement after room-and-pillar mining is only <br />predicted to be one foot. The subsidence monitoring program previously <br />mentioned will be used to more accurately predict impacts on the stream in <br />the future. Thickness of overburden is much less under Scullion Gulch than <br />Red Wash. The Staley-Gordon Mine, abandoned in 1970, has only 200 to <br />300 feet for overburden thickness, comparable to that under Scullion Gulch in <br />the Deserado Mine. No surface expressions of subsidence have been noted <br />over caved areas in the Staley-Gordon Mine. Examination by Western Fuels, <br />Inc. showed that the one known roof fall in this mine caused a collapse that <br />extended only 16 feet above the roof line where it was halted by a massive, <br />competent sandstone. <br />Tension cracks probably did occur above the Staley-Gordon Mine, but have <br />been healed by weathering. Similar tension cracks may cause several stock <br />ponds in the Scullion Gulch basin (within Federal Coal Leases C-8424 and <br />C-8425) to lose some impounded water. To prevent this loss, the permittee <br />may modify mining procedures beneath the pond areas. If the mine plan is <br />not modified, compensation for any water losses due to mining will be made. <br />The ponds will be repaired or replaced and water hauled in until the recovery <br />is complete (Page II. C-106c of the permit application). <br />See the Subsidence Section of this document for further details on impacts <br />related to subsidence. <br />19 <br />