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4.23 AUGER AND HIGHWALL MINING <br />4.23.1 Scope <br />This Section establishes environmental protection performance standards in addition to those <br />applicable performance standards in Rule 4, to prevent any unnecessary loss of coal reserves and <br />to prevent adverse enviromnental effects from auger mining incident to surface mining activities. <br />4.23.2 Performance Standards <br />4.23.2 Maximize Recoverability ofMineml Reserves <br />Colowyo has currently identified a number of areas that may be suitable for highwall mining that <br />will be accessed fi'om within the active East and West pits (refer to Map 23, Mineplan). Highwall <br />mining should allow for the recovery of additional coal resources beyond the currently permitted <br />pit final highwalls and endwalls. These resources were not classified as reserves until the <br />concept of highwall mining was conceived -all coal was previously classified as unmineable due <br />to being uneconomic to mine either by modern surface or underground mining methods. <br />From a strip mining perspective, the previously mined and firture permitted Limits of the East, <br />West, and Section 16 pits clearly delineate the maximum recoverable coal resources attainable <br />today with modern surface technology and coal market demand and pricing. The proposed <br />highwall mining of many of the same seams around the perimeter and underneath the mined out <br />pits, represents recovery of reserves that would not have been recovered by any other means <br />utilizing either surface or underground mining techniques. <br />The inability to recover these coal reserves by any other mining technique is primarily based on <br />insurmountable geologic factors. The majority of all coal seams experience splitting and thinning <br />to fhe point of not being economical to mine due to lack of adequate coal quality (unacceptable <br />ash from coal seam splits that cannot be selectively mined from the seam) and/or coal seam <br />thicknesses getting too thin to be mined from either the surface or underground. Additionally, all <br />coal seams proposed to be mined by highwall mining, have experienced natural historic in place <br />burning of the seams which severely limits the extent of mineable coal and also precludes finding <br />intact outcrop locations from which to access these same seams by underground outcrop mining. <br />To the north and east, changing geologic structure gives rise to severe dips and unstable fractured <br />strata that also precludes mining by either surface or underground mining methods. <br />Since the acquisition of Colowyo by Kennecott Energy Corporation in 1994, numerous <br />optimization, exploratory drilling, geologic evaluation, and pre-feasibility studies and programs <br />have been undertaken to identify all future mining options. By year-end 2003, Colowyo will <br />have pre-feasibility studies completed on three separate surface mining options and on <br />underground mining options that evaluated all coal seams and all areas within Colowyo's Logical <br />Mining Unit (LMU) and beyond. This comprehensive body of work has definitively and <br />unequivocally shown that all coal reserves proposed to be recovered by highwall mining methods <br />have already been depleted by the 27 plus years of mining activities in the West, East, and <br />Section 16 pits and are so limited in thickness and extent that it is not practical to recover the <br />remaining coal reserves by either surface or underground mining methods. At Colowyo, future <br />surface mining will entail moving to separate, disiinet, and in some cases distant pits while future <br />underground mining will entail mining totally different seams in different locations. <br />4.23.2 Undisturbed Areas of Coal Shall Be Left in Unmined Sections <br />Revision Date: 11/21/03 <br />RevisionNo.: TR-58 <br />Rule 4.23 4.23-1 <br />