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of draw. Slopes facing towards the mined -out area will result in larger angles of draw. At the present time, the
<br />influence of irregular topography on the angle of draw has yet to be quantified.
<br />It is anticipated that the irregular topography in the Permit Area will cause some variation in the angle of draw. This
<br />is consistent with preliminary observations from the longwall subsidence monitoring area above the No. 5 Mine where
<br />the steeper slope facing away from the gob area had a significantly reduced angle of draw. Three draw angles along
<br />monitoring lines, as shown on the Subsidence Monitoring Map (Map 31, were measured. The results of these
<br />measurements are shown on Table 86, Draw Angle Versus Slope and Orientation.
<br />A careful review and evaluation of the site-specific subsidence data and the site-specific geotechnical data determined
<br />the predicted angle of draw for the No. 5 and No. 6 Mines. This data was compared with research data from York
<br />Canyon, New Mexico (Gentry, Stewart, and King, 1981), Kemira Colliery, Australia, (Kapp, 1974), Paonia, Colorado
<br />(Dunrud, 1976), and Utah (Allgaier, 1982; and SUFCO, Personal Communication, 1986). The geotechnical
<br />environment in the permit is similar to that found throughout the MCM Mine complex as well as the various coalfields
<br />of the western United States. An angle of draw of 19 degrees is predicted as a conservative average draw angle for the
<br />permit area.
<br />SUBSIDENCE CONTROL PLAN
<br />MCM has prepared this Subsidence Control Plan to outline the proposed measures that may be taken, if required, to
<br />restore any affected structures or resource lands to their pre -subsidence condition. This section specifically addresses
<br />the structures present in the permit area. The only renewable resource lands potentially impacted by subsidence are
<br />the surface and subsurface water resources. The proposed mitigation measures for the surface and subsurface water
<br />resources are discussed in Section 2.05.6, Mitigation of the Impacts of Mining Operations.
<br />Mine Facilities (Presently Undermined)
<br />The mine facilities in the Permit Area that are presently undermined include mine roads, powerlines, water -lines, the
<br />railroad spur, the coal storage silo, and the coal transport facilities. These facilities, are presently located over
<br />development entries (mains and sub -mains) which are designed to remain stable for the life of the mine. These areas
<br />have been protected against subsidence damage by ensuring that sufficient coal was left in place to prevent or
<br />minimize subsidence in the area. Given the time period that has elapsed since these entries were developed, and that
<br />no discernible surface subsidence has been detected, the potential for any future subsidence is negligible, however, if
<br />subsidence were to occur and the structures or facilities were to be damaged, they will be repaired, replaced, or
<br />demolished and removed at MCM's option. In addition, areas of Trapper Mining, Inc.'s surface mining operation
<br />which have been previously mined and reclaimed have been partially undermined. The Trapper Mining reclaimed
<br />areas that have been undermined including reclaimed mine areas, two topsoil stockpiles, an access road leading to the
<br />topsoil stockpiles, and several small stock ponds were undermined without any material damage. While future
<br />subsidence is unlikely, if subsidence were to occur, MCM would assess any surface subsidence effects relative to
<br />potential stability and drainage effects, and make any necessary repairs, as indicated.
<br />Mine Facilities (To Be Undermined)
<br />The mine facilities under which proposed mining will take place include limited surface facilities and portions of
<br />MCM's underground mine workings. The MCM surface facilities that will be undermined include Sedimentation
<br />Ponds SH -P1, SH -P2 and the associated Old Shop and storage area (reclaimed in 2008), a rock dust tank, the
<br />contractor staging area, the Storage and wood shop, and the Okie Plaza Well. It is anticipated that a general lowering
<br />of the ground surface, localized changes in grade, and minor cracking may occur, and that any associated subsidence
<br />effects may necessitate minor repairs to these facilities. Ponds SH -P1 and SH -P2 and Ditches SH -132 and SH -D3 will
<br />be monitored closely during subsidence. Pre- and post -subsidence surveys and monthly inspections between surveys
<br />will be conducted. Any damage will be promptly repaired. The rock dust tank is no longer in use so no effects are
<br />TR14-36 2.05-63 Revised 03/10/14
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