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D,E%. -12' 96 (THU) 10:24 WRIGHT WATER <br />TEL:303 460 1020 <br />MEMORANDUM <br />TO. Jim Pendleton, Dave Berry, and Mike Boulay <br />Colorado Division of Minerals and Geology <br />FROM: Mountain Coal Company and <br />Wright Water Engineers <br />DATE: December 12, 1996 <br />RE: Key Points of Agreement in November 26`h Meeting <br />ill ~~II~II~I~I~I I~i 002 <br />We felt that it would be beneficial to put in writing some of the L•ey points of agreement <br />reached during the November 26"' meeting at the Colorado Division of Ivfinerals and Geology <br />(CDMG) regarding Mountain Coal Company's (MCC's) permit revisions (PRs). <br />Specifically, those PRs in which Wright Water Engineers (WWE) is involved. These <br />include: the Box Canyon PR; the probable hydrologic consequences (PHC) revision; and the <br />South of Divide (SOD) PR <br />A summary of the PHC revision discussion is being prepared separately by MCC and will not <br />be addressed in this memorandum with the exception of the surface cracks above Panel 8. <br />During the meeting, WWE provided an overview of the work that is being conducted in the <br />SOD perntit revision area in preparation for the PR application submittal. Consequently, this <br />memorandum focuses on key issues related to the Box Canyon PR <br />The three main topics discussed during the meeting relating to the Box Canyon PR were as <br />follows: (1) Block Movement, (2) Fraaure-Controlled Drainages, and (3) Landslides Neaz <br />the Mouth of Box Canyon. <br />BLOCK MOVEMENT <br />Mr. Dunrud of WWE presented a list of the important factors governing block movement <br />stability and the nature of those factor in the Box Canyon PR area A summary follows: <br />Dip Angle -Perhaps the single most important factor, a dip angle is excess of 8° usually <br />merits concern- In the vicinity of the Oliver No. 2 Mine the dip angle is 2°-3 ° and in the Box <br />Canyon PR area the dip angle is 1°-2°. The dip angle was compared with the angle of <br />internal friction for clays, which is typically in the range of 8°-17°. <br />Pore Fluid Pressare -One of the factors thought to be of concern in the vicinity of the Oliver <br />No. 2 Mine was the occurrence of methane and water. While these fluids were initially under <br />pressure when first encountered in the Oliver No. 2 Mine, both have continued to be released <br />since the mine closure. Consequently, the pore fluid pressures aze much lower than when the <br />Oliver No_ 2 Mine operations enwuntercd the inflows. Furthermore, during exploration <br />V <br />Z <br />W <br />W <br />Z <br />V <br />Z <br />W <br />fY <br />W <br />Q <br />3 <br />H <br />V <br />C, <br />