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RULE 4 PERFORMANCE STANDARDS <br /> <br />Collom – Rule 4, Page 21 Revision Date: 11/23/21 <br /> Revision No.: TR-152 <br />Colowyo does not plan to have concurrent surface or underground mining activities; therefore, the <br />requirements of this Section are not applicable to this permit application. <br /> <br />4.23 AUGER AND HIGHWALL MINING <br /> <br />Colowyo does plan to conduct highwall mining activities; therefore, the requirements of this Section will <br />be revised through the technical revision process prior to initiating any highwall mining in the Collom <br />mining area. <br /> <br />4.24 OPERATIONS IN ALLUVIAL VALLEY FLOORS <br /> <br />4.23 AUGER AND HIGHWALL MINING <br /> <br />4.23.1 Scope <br /> <br />Highwall mining allows for the recovery of additional coal resources beyond the final pit highwalls and <br />endwalls. Colowyo’s has previously effectively highwall mined in the East, Section 16, West, and South <br />Taylor Pits in the past. Colowyo will utizilied the vast experience gained from previous highwall mining <br />and implement a highwall mining plan in the Collom Pit. Please see Section 2.06.9 and Map 23B for the <br />seams and areas planned to be highwall mined. <br /> <br />From a surface mining perspective, the Collom Pit delineates the maximum recoverable coal resources <br />permitted by this mining permit for Colowyo to mine. Highwall mining in the Collom Pit will allow for <br />for maximum recovery in accordance with Rule 4.23.2(1). Please refer to Sections 2.06.9 in Volume 1 <br />for additional discussion regarding the removal of coal using highwall mining methods. <br /> <br />4.23.2 Performance Standards <br /> <br />4.23.2(1) Undisturbed Areas of Coal Shall be Left in Unmined Sections <br /> <br />As for the rules requirements [Rules 4.23.2(1)(a)-(c)] for leaving undisturbed areas of coal in unmined <br />sections, Colowyo requests a variance from the requirements of this rule for the Collom Pit. Colowyo’s <br />highly successful highwall mining methods that will be used in the Collom Pit, will maximize production <br />and ensure no subsidence occurs. Using this particular method of highwall mining by leaving pillars and <br />barriers allows the seams to be mined below each other and still ensures geologic stability once all seams <br />have been mined out. Please see Exhibit 27, Item 6 and Item 7 in Volume 20 for further discussion on <br />the geotechnical design and operational considerations implemented highwall mining the Collom Pit. <br /> <br />4.23.2(2) Abandoned or Active Underground Mine Workings <br /> <br />No abandoned or active underground mine workings have ever existed or currently exist anywhere near <br />the Collom Pit. Therefore, in accordance with Rule 4.23.2(2), no highwall mining activities will occur <br />closer than 500 feet in horizontal distance of any underground mining workings. <br /> <br />4.23.2(3) Contemporaneous Surface and Auger (Highwall) Mining <br /> <br />Highwall mining will follow the surface coal mining activities in a top-down sequence in the Collom Pit. <br />Highwall mining has to occur as contemporaneous as possible behind surface mining to ensure further <br />advancement of the Collom box cut is not hindered by highwall mining operations. When surface <br />mining opens up a large enough area in the Collom Pit, highwall mining will commence shortly