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© T e r r a M a t r i x <br />MONTGOMERY WATSON <br />NaturalNesource Group <br />September 19, 1997 <br />Mr. William J. Carter <br />Colorado Division of Minerals & Geology <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />(303) 866-3567 <br />-- - <br />~II ~I~~I~II~~~~~~I~ <br />sss <br />RECEIVED <br />JAN 2 3 1998 <br />Division of Minerals & Geobgy <br />Re: Oxbow Carbon & Minerals, Inc. -Somerset and Sanborn Creek Miner (Permit o. C-81- <br />022), Technical Revision TR-29 -Stipulation 28 <br />Dear Mr. Carter: <br />Accompanying this transmittal is a report addressing the projected subsidence impacts due to <br />longwall mining as proposed under the previously submitted and approved Technical <br />Revision TR-29. This report is submitted for inclusion in the permit application document <br />as Appendix J-1 and in partial fulfillment of the specific requirement of Stipulation 28 to the <br />DMG's approval of TR-29. <br />The accompanying report, prepazed by John F. Abel, Jr., evaluates all potential subsidence <br />mechanisms and associated subsidence-related impacts resulting in the following general <br />conclusions: <br />• Surface subsidence effects and subsidence of overlying mine workings will be <br />limited to trough subsidence <br />• Chimney subsidence is unlikely to develop and if it does would not extend to <br />the overlying D Seam <br />• Maximum trough subsidence will be associated with and will result from <br />progressive mining of each set of three adjacent longwall panels <br />• Actual vertical subsidence will probably not exceed two-thirds of the maximum <br />projected subsidence due to the conservative assumptions and calculation <br />methods utilized <br />• Maximum trough subsidence is projected to range from 9.03 to 11.63 feet <br />• Maximum projected horizontal tensile strains at the ground surface are projected <br />to range from 5,660 to 9,080 µe with strains at the upper end of this range <br />potentially resulting in open fractures up to 1-foot in width at the ground surface <br />• Maximum projected horizontal compressive strains at the ground surface are <br />projected to range from 10,960 to 15,060 µe with strains at the upper end of this <br />range potentially resulting in compression ridges up to 1-foot in height at the <br />ground surface. <br />PO Roy 774018 Tel ~ 970 879 fi2fi0 Serving the YVorld's Environmental Needs <br />i a75 Pine Grove Road Fax. 970 879 90x8 <br />Sieamhnat SPnnys, Colorado <br />8077 <br />