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RULE 4 PERFORMANCE STANDARDS <br />coal reserves proposed to be recovered by highwall mining methods have already been depleted <br />by the 27 plus years of mining activities in the West, East, and Section 16 pits and are so limited <br />in thickness and extent that it is not practical to recover the remaining coal reserves by either <br />surface or underground mining methods. At Colowyo, future surface mining will entail moving <br />to separate, distinct, and in some cases distant pits while future underground mining will entail <br />mining totally different seams in different locations. <br />4.23.5 Undisturbed Areas of Coal Shall Be Left in Unmined Sections <br />As for the CDRMS Rules (Rules) requirement for leaving undisturbed areas of coal in unmined <br />sections, Colowyo contends that this application of the Rules does not apply since the seams to <br />be highwall mined are being accessed from active surface pits that by this Permit and other <br />applicable sections of the Rules are required to be backfilled and fully reclaimed. Hence should <br />undisturbed barrier areas of coal be left for some future access, these potential portal areas would <br />be inaccessible for future generations because they would be buried under the pit backfill. <br />Additionally and importantly, as discussed above, due to the many geological reasons, there is <br />not economical coal to be recovered from "behind" the areas slated to be highwall mined. <br />4.23.6 Abandoned or Active Underground Mine Workings <br />To Colowyo's knowledge, no abandoned or active underground mine workings have ever existed <br />or currently exist in any of the coal seams in the areas proposed to be highwall mined. No <br />highwall mining will be allowed to take place within 500 feet of any abandoned or active <br />underground mining operation. <br />4.23.7 Surface Mining Activities and Highwall Mining <br />The highwall mining shall follow the surface coal mining activities in a contemporaneous <br />manner consistent with the applicable requirements of CDRMS Rule 4. Due to active pit <br />progressions and sequencing of mining (in addition to meeting the Permit requirements for <br />contemporaneous reclamation), it is required that highwall mining occurs timely if not <br />immediately following conclusion of pit mining activities. Also, as described more fully in <br />2.06.9(2), the need to backfill, ie, contemporaneously reclaim the pits, is mandatory for Colowyo <br />in order to build the pit floor from which to work from to mine the successively higher (in the <br />geologic column) coal seam. Hence successful highwall mining is in part dependant upon timely <br />and successful contemporaneous reclamation of the pits. <br />4.23.8 Prevent Pollution of Surface and Groundwater and to Reduce Fire Hazards <br />Ground water in the pit or highwall mining holes will not be problematic being that the Colowyo <br />pits are essentially dry (minor perched aquifers with limited seasonal flows) and are located <br />above the 1St regional aquifer (Trout Creek) by a substantial distance. Ground water flow <br />regimes and the negligible impact that Colowyo's surface mining activities have on ground water <br />as a result of mining these target coal seams/rock interburdens are detailed extensively in Permit <br />Section 2.04.7(1). From this extensive body of data and from experiences to date with mining <br />activities, no toxic forming or acid forming water discharge is anticipated from any of the <br />Rule 4 Performance Standards 4-88 Revision Date: 4/2/18 <br />Revision No.: RN -07 <br />