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STATE OF COLORADO <br />DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866-3567 <br />FAX: (303) 832-8106 <br />March 16, 2010 <br /> <br />COLORADO <br />D I V I S ION OF <br />RECLAMATION <br />MINING <br />SAFETY <br />Bill Ritter, Jr. <br />Governor <br />F.Av Harris D. Sherman <br />VqXwW Executive Director <br />/ Ryan Ellis 9 207 Ronald W. Cattany <br />MAR 1 <br />Greg Lewicki and Associates Division Director <br />afion, Natural Resource Trustee <br />11541 Warrington Court DWilita ? <br />Parker, CO 80138 safety <br />f <br />Re: Cugnini Pit, Permit M-1986-061, Amendment AM-2, Preliminary Adequacy Review Letter. <br />Dear Mr. Ellis, <br />This office has completed the preliminary review for technical adequacy of the amendment application <br />named above. There are a number of items that still require clarification or additional information, and they <br />are listed in the paragraphs below. Any exhibits that are considered adequate at this time are not included in <br />this letter. Please address all items, and identify your responses with the exhibit to which they pertain. <br />Exhibit C - Pre-mining and Mining Plan Maps (Rule 6.4.3) <br />The pre-mining map (Map C-2A) does not show Cugnini Water Well #2, though it is shown on the mining <br />plan map (Map C-2B). Please clarify whether this well currently exists. <br />The pre-mining map depicts Valley Fill #1 as a completed feature, with a 2:1 backfill slope and surface <br />drainage structures currently in place. Until this office can perform the pre-operation inspection and assess <br />these onsite features, we must presume that they are adequately reflected on the map and are stable as <br />constructed. Have there been any stability issues or reclamation difficulties with the 2:1 backfill slope? <br />Have there been any issues with settling or voids associated with the deep fills or impoundment berm? <br />Exhibit D - Mining Plan (Rule 6.4.4) <br />The plan states that the deposit to be mined is a 30-foot deep layer of aggregate, which will be mined down <br />to the underlying shale layer. This shale layer daylights on the native slope to the east. An unfractured shale <br />layer, which this might be, may restrict deeper percolation of groundwater and result in the formation of <br />seeps along that east slope, especially when the thick layer of native aggregate is removed. Such seeps may <br />cause instability especially if an insufficient depth of backfill (overburden, topsoil, etc.) is replaced. An <br />adequate depth of material must be retained for backfill and/or sufficient depth of aggregate left unmined <br />above the shale, to provide better stability and drainage control. Please state what the minimum depth of <br />material will be above the shale layer. <br />The plan states that Cugnini Water Well #2 is to be used to supply water to the operation, and Exhibit G <br />contains some water well information, but it is not clear that this is the well that is approved by the State <br />Office of Office of <br />Mined Land Reclamation Denver • Grand )unction • Durango Active and Inactive Mines