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J. ~. STOVER & ASSOCI~ES ~IIII~~~II~~~~~~~~~ <br />2768 COMPASS DRIVE, SUITE 101 <br />GRAND JUNCTION, COLORADO 81506 <br />PHONE: (970) 245-4101, FAB 242-7908 <br />MINE ENGINEERING CIVIL ENGINEERING <br />MINB RECLTNATION CONSTRUCTION NANACENENT <br />September 18, 1996 <br />L <br />kt' y i9:9& <br />Susan L. Burgmaier <br />Division of Minerals and Geology <br />1313 Sherman St., Room 215 <br />Denver, CO 80203 <br />Re: Oxbow Carbon & Minerals <br />Permit Revision (PR-03) <br />160 Acre Lease Modification <br />Permit C-81-022 <br /> <br />Dear Ms. Burgmaier: <br />The DMG's letter dated September 12, <br />on the subsidence related aspects <br />Following are OCM's responses to the <br />1996 transmitted its comments <br />of the proposed revision. <br />DMG's concerns: <br />The DMG's concern is with OCM's proposal to control subsidence by <br />limiting extraction to 50$ without providing predictive evidence to <br />support the extraction limit as an appropriate control methodology. <br />The areas of concern are portions of the DMEA powerline and Hubbard <br />Creek. Only first or development mining was performed under <br />Hubbard Creek. The mining under Hubbard Creek was performed in <br />1984. Visual and survey monitoring did not detect any significant <br />subsidence caused by the limited mining under Hubbard Creek (ref. <br />TR-03 with a decision date of December 30, 1986). <br />The DMEA powerline was undermined in two locations. The western <br />location was undermined in mid 1993. The eastern location was <br />undermined in mid 1994 to facilitate the installation of OCM's <br />Substation No. 3. Based on visual inspections of the two <br />locations, the DMEA powerline has not been adversely affected by <br />the mining. <br />Enclosed are revised pages 2.05-58 and 2.05-59 which present <br />empirical evidence that a 508 extraction limit will control <br />subsidence. <br />The entire section 2.05.6(6) was reprinted with new page numbers <br />2.05-55 through 2.05-61 so the complete revised section is <br />enclosed. The primary change in the discussion for this section is <br />presented on revised pages 2.05-58 and 2.05-59. Also enclosed are <br />three copies of map 5-008, Subsidence Prediction Plan. The croas- <br />