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Mr. Dennis Conn - 3 - June 20, 1989 B. Amendments to the F-Seam Mine Plan (continued) Pile permit revision. The Division disallowed retreat extraction beneath the pile and the immediately adjoining area. Because slope instability had occurred in the surficial deposits immediately above the portals of the Mt. Gunnison No. 1 Mine, the Division required additional surface monumentation and stability monitoring be conducted at the pile site. The Division specified the installation and monitoring of several electronic tilt meter tables downslooe from the toe of the orooosed pile, prior to any disturbance of the site. In the fall of 1985 West Elk Coal Company submitted a permit revision application requesting aooroval of a permanent Lower Waste Pile to be located adjoining the mouth of Sylvester Gulch, and the Uooer Waste Pile has yet to be constructed. Assuming retreat extraction of the area, the applicant's projection that subsidence of the orooosed site should occur rapidly is plausible. In order to obtain aooroval to retreat mine these orooosed panels, however, the existing permit revision for the Upper Waste Pile must be amended. I believe such an aooroval would be appropriate, if the applicant were to install a subsidence monitoring network to verify that the projected subsidence did occur and that the stability of the foundational area was not deleteriously affected. Another Dart of the F-Seam mine plan amendment occupies the southeast portion of the five year mine plan area. The aoolicant proposes to discontinue easterly advance of the 1st East Submain, because of bad roof conditions adjoining S.vlvester Gulch. The proposed alternative is to advance a new set of East Submain Entries to the east southeast, and then drive a series of 9 panels (lE1N through lE9N) to the east northeast. Limited extraction within the East Submains will probably prevent subsidence from impacting adjoining areas to the south of the Minnesota reek drainage divide. However, the applicant should specify what engineering precaution will be taken to prevent impacts south of the drainage divide. This should include, at a minimum, specification of a limited extraction plan for the East Submain Entries and the delineation of the area of the plan in which the limited extraction plan will be employed to ensure prevention of subsidence south of the divide. C. Subsidence Evaluation and Control Plan The B-Seam permit revision application contains a subsidence evaluation within Exhibit 3.4.A.6. This evaluation, entitled "Subsidence Evaluation for Mt. Gunnison No. 1 Mine, Revision No. 1" is a revision of the earlier permit renewal application's Exhibit 3.4.S.A. This original Exhibit 3.4.8.A contained a discussion of the implications of projected subsidence for the various protected areas within the permit area, including structures, renewable resource lands, and geological hazards. Neither the B-Seam permit revision application text nor Exhibit 3.4.A.6 contain any reference to, or discussion of, the implications of projected subsidence for the protected areas within the permit area. The applicant will have to address the implications of the significantly increased potential maximum vertical subsidence magnitude for the protected areas of the permit, in order to fulfill the requirements of Rule 2.05.6(6)(bl.