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IX. Subsidence: Several problans arise in considering the subsidence aspects of the perrnit renewal application. The renewal application reflects the changes in mine plan and subsidence rrunitoring acccrrplished within the current revised permit, with one exception. During the past month, west Elk Coal Carpany corresponded with the Division regarding sore problans implarenting a portion of their approved subsidence monitoring program. This very recent correspondence should be added to the Addendun Section of Exhibit 3.4.8A of the permit renewal application. The correspondence consisted of a letter from 1Vest Elk to Susan ~~bwry, dated February 2l, 1936, and a response from Susan to the operator, dated ~4larch 4, 1986, with an attached rnaro fran myself to Susan, dated February 25, 1986. A more complex problem arises concerning the Life-of-dine Plan subsidence projections. Because of recent judicial decisions, we will need to carplete a revised Cumulative Hydrologic Impact Staterent (4-[IS) for "all anticipated mining." This will include all mining anticipated to occur within the leases held by West Elk Coal. The Life-of-~bline Plan depicted on Exhibit 3.4.4.B.1 appears to depict all anticipated mining, for purposes of the required Q-IIS. The renewal application proposes to control possible subsidence impacts to critical areas, such as the Dry Fork of Minnesota Creek and Lick Creek, through the use of a plan of limited extraction. Exhibit 3.4.4.8.1 schanatically depicts a buffer adjoining the Dry Fork channel. The operator requests approval to extract up *.o SCf,6 of the in-place coal beneath this buffer zone. The same schene was presented within the original permit application. However, in preparing our findings for the original application, The Division did not include the areas south of the drainage divide between the iVorth Fork and the Dry Fork within the anticipated mining. Therefore, we only stated that the proposed limited extraction plan would be perfected through use of subsidence monitoring data before such extraction was finally approved. For purposes of preparing a detailed Q-115 including the areas south of the divide, WECC will need to more explicitly define the plan for limited extraction and the areas within which it will be applied. [t will be necessary to define a discrete boundary for the buffer zones. Buffer zones will need to be designated adjoining both the Dry Fork of tvlinnesota Creek and Lick Creek. Buffer zones will need to be projected fran the alluvial deposit boundaries adjoining the surface channel, not the centerline of the channel. Extraction will need to be limited to sore level significantly less than Sa:S, until the operator provides subsidence monitoring and hydrology monitoring data with which to verify the propriety of that extraction level. Finally, the width of the appropriate buffer zone will need to be determined. IX-l