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Page 2 of 2 <br />DBMS: Rule 2.05.3(6) states that "Temporary overburden disposal (storage) structures shall comply with the <br />applicable performance standards of Rule 4." Shannon & Wilson's Addendum No. 4 analyzes the excess spoil <br />pile in its entirety which includes both the proposed temporary excess spoil and the previously approved <br />permanent excess spoil pile. In Shannon & and Wilson's slope stability analysis of the entire excess spoil pile, <br />their report shows potential failure paths through both temporary and permanent sections of the fill. Since the <br />additional load of the proposed temporary excess spoil fill has potential effects on the long -term stability of the <br />currently approved permanent excess spoil pile, the Division believes that Rule 4.09.1(7), regarding long -term <br />static safety factor of 1.5, is applicable for this situation. <br />However, after further review, the Division finds that Colowyo has satisfied these rules by showing a long -term <br />static safety factor in excess of 1.8 using average test values attained from field samples. No additional comments <br />are needed. <br />Item 2 <br />DBMS: Shannon &Wilson's analysis does not address the fact that some of the proposed excess spoil would <br />overlay an area of highwall mining. Please address the potential impact of the additional load from the proposed <br />excess spoil fill on the excavated sections from highwall mining as well as the integrity of the proposed excess <br />spoil fill. <br />Colowyo: In Exhibit 21, Item 1, Addendum No. 3 -6, potential highwall mining impacts have been presented and <br />approved by the Division previously. Colowyo believes this section of the report addressing highwall mining in <br />the vicinity of the proposed spoil pile adequately addresses potential impacts from previously preformed highwall <br />mining below the permanent West Taylor Fill. <br />DBMS: Potential impacts on excess spoil piles from previously performed highwall mining have been adequately <br />addressed in Exhibit 21, Item 1, Addendum No. 3 -6. No additional comments are needed. <br />Item 3 <br />DBMS: Please add information to the appropriate text and to Map 45 showing how drainage from the temporary <br />spoil pile will drain to the pit. <br />Colowyo: Per Rule 4.05.2(1), `All surface drainage from the disturbed area is required to be routed through a <br />sedimentation pond or a series of sedimentation ponds, or other treatment facilities before leaving the permit <br />area. " Therefore, should Colowyo desire to retain drainage from the temporary spoil pile in pit there are no <br />requirements for Colowyo to demonstrate to the Division how it will contain runoff within the confines of the pit. <br />Nonetheless, Colowyo is required under MSHA standards to have berms that are half the axle height to the <br />largest equipment that will potentially utilize an elevated roadway. The roadway on the North side of the <br />temporary spoil pile will be bermed accordingly which will not allow any surface drainage to the West Taylor <br />Pond. Colowyo will manage this water into the South Taylor Pit as it deems necessary through use of the berms, <br />ditches, and /or pumping. <br />DBMS: Rule 2.05.6(3)(b)(i) requires that Colowyo's PAP includes a plan to control surface water within the <br />permit area. However, drainage from temporary spoil piles to pits has not been shown on Map 45 or other maps <br />in the past. Through inspections, the Division shall confirm that this runoff does in fact drain to the pit. No <br />additional comments are needed. <br />All three items are resolved. When the Division has completed the Reclamation Cost Estimate associated with TR- <br />98, a proposed decision approving this application will be issued. <br />Please contact me (extension 8113) if you have any questions. <br />Sincerely, <br />a-� 1 ;7�, <br />Robert Zuber, P.E. <br />Environmental Protection Specialist <br />