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N Randy Price - 2 - June 10, 1986 resulting tension cracks... The long-term effects are associated primarily with rubblization of the immediate roof and the developement of chimney subsidence causing permanent changes in shear strength conditions in the sub-surface and in the hydrogeologic conditions. These effects may be minimized through control of subsidence near the outcrop when overburden thicknesses fall to where it is possible for chimney subsidence to develop." The report contains state-of-the-art slope stability and subsidence analyses and I believe that the consultant's conclusions are prudent. In keeping with Stipulation No. 7, the report proposes that a minor limitation of extraction be superimposed upon the originally approved mine plan in the near outcrop portions of the Bear No. 3 Mine. As depicted on Figure B7, contained in Appendix B of the report, the operator proposes a minimum two hundred foot wide undisturbed outcrop barrier pillar. In actuality, as depicted upon Figure B7, the undisturbed barrier pillar will probably exceed two hundred feet in width, as determined by coal conditions. Further, inside the undisturbed barrier pillar, the operator proposes a zone in which pillars will be split, but not completely mined, resulting in a maximum coal extraction rate of approximately seventy percent. This proposed pillar-split zone has been defined by locating the base of the massive sandstone outcrop exposed on the slope approximately three hundred feet above the "C" seam outcrop and projecting the edge of the zone back towards the coal outcrop at an angle of 27° from vertical (projected angle of break). This massive sandstone is projected to bridge the subsidence troughing caused by extraction within the "C" seam. Factors of safety within these split pillars are projected to exceed 1.5, and should be capable of producing long-term stability. The consultant theorizes; "The net effect of this split-pillar zone will be less total subsidence and a gradual transition zone between areas of no subsidence and maximum subsidence. This will substantially reduce the developement of tensile strain in this area and further reduce the probability of chimney subsidence." On page 28 of the report, Rocky Mountain Geotechnical, Inc., recommends that the existing subsidence monitoring monuments be monitored at regular intervals " ..prior to, during and after all retreat mining until the associated subsidence is complete in order to verify assumptions made and conclusions drawn in this study." The consultant further recommends "...visual inspection of the surface above areas to be subsided in order to further substantiate or refute the conclusions of this study." I concur with both of these suggestions and recommend that we condition our acceptance of the operator's stipulation response upon their continuation of subsidence monitoring and associated visual inspections of the subsided area, until cessation is approved by the Division, in writing. JAP/ddt cc: Bob Liddle 1056E