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`'' I' • • III III III III IIII III <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Depar(mem of Natural Resources I~~~~~ <br />1317 Sherman SL, Room 215 <br />Denver, Colorado 80203 <br />Phone: (3031 866-7567 <br />FA%. (3031 832-8106 <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES '~ <br />DATE: January 6, 1995 Roy Romer <br />Governor <br />TO: Be an fel Tames S. LOChhead <br />Exec Wive Dnector <br />Michael B. Long <br />FROM: Ca Moun Division Dveuor <br />RE: Proposed possible capping of various areas of the <br />Cresson Mine, Permit M-80-244 <br />I have reviewed the proposed capping concept that was included in <br />your memo of December 29, 1994. I offer the following comments: <br />1. Capping needs to ensure that water and air flow through the <br />material to be capped is reduced and controlled thus lessening <br />the ability foY the material capped to generate acid mine <br />drainage (if the material will do so). Therefore, it is hard <br />to evaluate the proposal as anything more than a cross section <br />of the cap cover. The cap cover must also be protected so it <br />will remain on the capped material for as long as possible. <br />2. I agree that 12 inches minimum topsoil material at the final <br />surface is a good idea. We still haven't seen any volume <br />estimates of topsoil saved that indicate that enough topsoil <br />is available for this capping scheme. I would want to see <br />what type of erosional stability is shown by the types of <br />topsoils available in this area and key that to the steepest <br />slope angles that should be allowed. 2.5H:1V slopes may be <br />too steep depending on erosion rates. <br />3. Plant species used on the cap should be shallow rooted species <br />to lessen the possibility of root penetration of the cap <br />material. Root penetration would enhance water flow into the <br />material being capped, an effect that would increase the <br />possibility of acid and metal drainage. <br />4. As others have already pointed out, the 3 feet of overburden <br />should consist of non acid forming or metal generating <br />material. Additionally, this material should be amenable to <br />plant growth and root penetration and have the permeability to <br />act as a de facto drainage layer to help keep water out of the <br />compacted overburden layer below. <br />