1992-02-10_GENERAL DOCUMENTS - C1981017 (2)

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.00 -3- between the worked-out area and these two locations are 32 . 680 and 8 . 490 respectively. The facts that (a ) this crack virtually parallels the ridge line, rather than the edge of the longwall panel, (b) its maximum development is at the maximum distance (980 feet ) and angle ( 32 . 68 ) from the edge of the mined-area while it disappears at both ends at much closer distances ( 475 feet and 250 feet respectively) , and ( ) that its maximum development is on or immediately adjacent to an old slump block all suggest that this crack is a natural ridge-line slump feature, related to mining only indirectly if at all . While it is possibls that subsidence within the projected angle of draw of 18 could have triggered sympathetic fracturing progressing up the steep slope of the ridge, a careful examinationof the grass-covered and bare rock surface of the bowll below the ridge line, toward the mined- out area, from the ridge revealed no other cracks, or pits, cratered ground, slumps, landslides or other signs of disturbance whatsoever . A subsidence-related explanation for the parallel crack on the back side of the ridge is even more difficult to establish. It is therefore concluded, based on the evidence at hand, that these features are naturally-occurring ridge-line slump features, with the larger crack a possible reactivation of ancient slip planes related to an old slump block, all triggered by natural processes, primarily the greater-than-normal precipitation experienced in the period from 1981 through 1986 . MCR recognizes that Stipulation No. 1 of the agreement dated January 29, 1986, requires the immediate resumption of the subsidence monitoring program in the event such features as described above are detected within the area 0potentially affected by subsidence (angle of draw = 20 . 5 , see further discussion below) . However, in this case the cracks discovered occur both within and outside this area, with the greatest development at maximum distance and angle from mined-out areas, and there are no subsidence monitoring or control points in the area of either feature, the monitoring of which would have any bearing on establishing a mining- related cause or determining potential effects . MCR therefore requests that resumption of the monitoring program be limited to annual visual inspection and reporting. The worst-case effect of continued development of these cracks, whether the are natural, as concluded herein based on evidence availab e at this writing, or subsidence- induced, would be a slump, similar to the old slump block existing in the area, involving ridge-line materials into the bowl above the aeadwaters of the south fork of Coal Creek . No structures, aquifers or renewable resource lands would be involved ( elevation of the saddle itself is 11, 566 feet; only a few scrub evergreens and sparse grass exist at this elevation) . it is possible that, depending on the