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deposilS of other minerals in the sam~land with su.:abie sc:r._a lions for simultaneous operation (43 CFR Ch. L1, 3400.1). • Hvdro lofty Dua to the nature of subsidence over a Longwell system, the disturbance to the hydrological flow in and below the drainages is expected to be mini- mal. Subsidence occurs in a wave action following the longwall face. The extent of horizontal reaction in front of the longwall face is dependent on the angle of draw. As the longwall passes, cracks will open as the ground is placed in tension and then close as the stress wave proceeds beyond any given location. It is generally believed that any cracks that develop in the crust will be discontinuous. It is not considered possible Eor water to Elow from the surface and enter the mine area. There are 600-1,200 feet aE overburden above the coal seam in the Red Wash area. When the coal is extracted the roof caves immedi- ately behind the longwall. The swell of the shales and sandstones soon EiLls the open cavity. There will be no active collapse and caving more than 30-40 feet above the top of the seam. Following the initial violent caving of the immediate roof, the overlying strata will deflect slowly with only minimal fracturing. Tension cracks will form in the crust and in the secondary layer in the creek bottom. However, the thick Layer of fine silt present in the drain- age eyatems is predicted to hide and quickly seal off any openings. The effect of subsidence on the groundwater under the Red Wash is unpredict- able and purely speculative. The data derived from monitoring the first room and pillar and longwall panels will enable Western Fuels to make accurate predictions of subsid- ence and strain over subsequent panels. It will be possible to make accurate predictions of the timing and magnitude of any subsidence that may affect the county road, so that Western Fuels can take appropriate actions, i.e., repairs and traffic control. Similar predictions will also be possible for panels that may produce subsidence near Red Wash. Soils The subsidence rill cause some settling and cracking of the soils and sub- sequent offsetting at the surface up to S feat high. Following natural filling, rasloping, and seeding this should be a minor impact. The access roads and drill arena Eor the construction of the degas ificatian wells rill caua• surfae• disturbance of up to 7 acres in the lease application area. X11 coada, well areas, and associated disturbances will have to be recontoured and revegetatad before abandonment of the location. Some soil erosion could take place until these areas ors stabilized. Overall impacts should not ba significant. U 16