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to range from 60-in (for the 1,400 ft depth to coal seam) to 67-in (for the 1,100 ft depth to coal seam). B. Maximum subsidence over the first panel in a sequence of panels is always less than subsidence over the subseque t~anels. The predicted maximum subsidence for 12R is 60-in as raft-b®-seen in Figures 2 and 4 of the AVF report. (~lE-3?~ C. Maximum subsidence is offset 100-ff to the north of each panel centerline due to seam dip. The source zone shown on Figure 1 of Exhibit 7F-1 is located south of the panel center where subsidence is further reduced (from maximum). D. Subsidence in the source zone is further influenced by its proximity to the start room of Panel 12R. Maximum subsidence will not develop until point ~, located approximately full depth or 1,100 ft from the start room. The source zone immediately above the road is located between 400 and 800-ft from the start room of Panel 12R. April 10, 2000A11 of these factors are built into the prediction of 30-in subsidence at the source zone. Sl~~ -? (w...-~- 3,,,~ S . l o,r~< <.~ --il.~,~- 7 18. In addition to the early, 1994 subsidence monitoring, extensive subsidence measurements have also been carried out along the County Road and Railroad that crosses the Eastern Mining District. Twentymile has proposed continued monitoring of County Road 33 as it is influenced by Panel 12R from a point 1000- ft east of the start room to the point where the 9R monitoring program began. In addition, detailed measurements will be made along the railroad alignment providing confirmation of the angle of draw, profile shape, and maximum subsidence for the fully developed profile of 12R. 19. The recommendations provided in the Rockfall hazards report are based on the assessment that cliff failure above County Road 33 in the 12R Study Area is unlikely. The proposal to close the road for short periods (i.e., hours at a time) to remove loose rock blocks from the top of the outcrop or source zone is a precautionary action based on a conservative approach to risk management. It should also be emphasized that this area of the Twentymile sandstone outcrop differs significantly from areas that previously failed in regard to topographic relief, foreslope conditions, and magnitude of predicted subsidence and strain. However, if the primary concern of the reviewer is stability of the cliff following mining, Twentymile will carry out a survey of the outcrop following undermining and report the results of this survey, along with any recommendations, to DOGM. If [his approach does no[ completely resolve your comment, may we suggest a field meeting to enable presentation, review, and resolution of your detailed concerns. 20. TCC will follow the recommendation in Exhibit 7F-1. 21. Please see comments to responses l9 and 22.