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~ ADDENDUM <br />~. SUBSIDENCE STUDY ~R PROPOSED LONG~PERf4 LEASE AREA <br />ORCHARD VALLEY QJAL MINE BY GEC-HYDRO ODNSULTING, INC. <br />Colorado Westmoreland Inc. contracted the services of Geo-klydro Consulting, <br />Inc. to prepare a site-specific study concerning projected subsidence <br />resul ting Fran coal mining of Eiederal Lease C-37210. This report, canpleted <br />during June, 1983, was incorporated into CWI's permit application, fulfil- <br />ling State k~gulatory Requirements for Section 2.05.6 -Mitigation of Sur- <br />face Coal Mining Operation Impacts. <br />Upon Division review of the permit application, several canments required <br />clarification. In cooperation with Ceo•-Hydro Consulting, Inc „ Colorado <br />Westmoreland Inc, has prepared the follaaing information. <br />The response to deficiency canments dated October 23, 1984, are cross <br />referenced to the permit application and are addressed in the order they are <br />listed, starting on page 18, canment 4. <br />A. A description of Renewable Resource Lands is located in Section <br />2,05.6(6)(a)(ii)A. <br />B, A program describing data collection, design procedures, and oxidation <br />of the coal seam is located in the Pillar Stability and Outcrop Barrier <br />Pillar Report, Volume 2, <br />C. Pdditional widely spaced monuments will not be emplaced during this per <br />mit teem, as described in Section 2,05.6(6)(c)(i)(B), <br />D. Undermining of critical areas is not scheduled for this permit tem or <br />prior to the time at which site specific subsidence data would Ltcane <br />available, as described in Section 2,05.6{6)(c)(i)(B). <br />E. Supporting calculations based upon Wilson's (1972) yielding pillar <br />design method are located in the Pillar Stability Report, Volume 2. <br />E. The statement quoted fran page 43, paragraph 1 contains a typing error; <br />it should read "maximum probable changes in the stream gradient would be <br />on the order of 1 to 3 percent." The existing stream gradients would <br />then not be altered by more than this maximum change in gradient, corn <br />servatively taken to be 3 percent. Since the existing stream gradients <br />are a1 the order of 6 to 10 percent, the lowest stream gradients wi~ich <br />could result fran subsidence are estimated to be 3 to 7 percent. This <br />indicates that there will be no reversal of stream gradients. <br />The change in gradients due to subsidence can be estimated Fran the con- <br />tours of estimated subsidence presented on Plate 14. These contours <br />Have been developed fran detailed calculations of surface subsidence <br />profiles, <br />1.-_J <br />