2011-01-13_PERMIT FILE - C1981038A (7)

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42.05 APPLICATION FOR PERMIT FOR SURFACE OR UNDERGROUND MINZNG ACTIVITIES -- MINIMUM REQUIREMENTS FOR OPERATION AND RECLAMATION PLANS. 2.05.6 Mitigation of Surface Coal Mining Operation Impacts. (Cont'd,) (6) (d) (i) (Cont'd.) August 6, 1982, development mining in the 8E- 25 panel commenced during January, 1983. Pil- lar recovery occurred March through May, 1983, and the August, 1983 survey depicted signifi- cant station movement; 1.06 ft. drop in eleva- tion and 1.447 ft. to the north. SubseQUent surveys (October, 1983 through October, 1984) have shown minimal station movement. Several observations can be made from this data (refer to the Monument Movement, Widely Spaced Grid Table (4)8) in the Subsidence Appendix in Vol- ume 3). First, subsidence occurs contempora- neous with pillar extraction and residual sub- sidence is practically nonexistent. Second, a predicted subsidence factor of 0.7 was sub- stantiated for this one condition at the Or- chard Valley Mine, Third, the methodology and assumptions derived from the Subsidence Engi- • peer's Handbook and applied by Geo-Hydro are valid for this one condition. In summary, CWI has gathered and evaluated a small amount of subsidence monitoring data. So far, this data has matched the information presented in the Geo-Hydro Subsidence Survey. It is too early to determine the total accura- cy of the subsidence prediction. CWI will continue extensive subsidence monitoring as previously stated. CWI has also submitted a subsidence control plan to satisfy lease stip- ulations. This plan is found in Section 2.05.6(6)(f) . (ii) If the Division determines, after consultation with CWI, that imminent danger of material subsidence damage or diminution of foreseeable use of the permit area exists, Colorado West- moreland will suspend undermining of identi- fied structures. (e) A subsidence survey, prepared by Geo-Hydro Consulting, Inc., qualified professionals on this subject, is based Revised 08/01(84 Added 12/26/84 Revised 12/26J84 Revised 10/12/86 Revised 10/01/87 150