2014-04-30_REVISION - C1981012 (2)

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DIVISION OF RECLAMATION, MINING AND SAFETY Department of Natural Resources 1313 Sherman St., Room 215 Denver, Colorado 80203 Phone: (303) 866 -3567 FAX: (303) 832 -8106 STATE OF COLORADO COLORADO D I V I S I ON OF RECLAMATION MINING SAFETY John W. Hickenlooper Governor April 30, 2014 Mike King Executive Director To: File Loretta E. Pineda !� Director From: Leigh Simmons Re: New Elk Mine (Permit No. C- 1981 -012) Technical Revision No. 69 Re. NECC response to initial adequacy review This memo is intended to document the review of materials that were submitted for TR69 in response to the initial adequacy review letter of April 3, 2014. New Elk Coal Company (NECC) submitted TR69, as well as completing work on the ground, in order to abate NOV CV- 2013 -009. TR69 sought to reconcile the design of the RDA upland diversion ditch with the physical constraints that were encountered in the field. In reviewing the approved Permit Appliaction Packet (PAP) for material pertaining to the design of the ditch, several ambiguities and apparent inconsistencies were discovered by the Division. The approved TR updates table 20 to include two rows for ditch D55, each of which refers to a SedCad design added to exhibit 19. The two designs are for ditches with gradients of 2.75 %, and 15.3 %, each of which is a triangular section ditch designed to convey the 100y /24hr event (a discharge of 13.9 cfs). The designs call for 2.0:1 sideslope ratios and 0.30' of freeboard, with depths and top widths of 1.54' and 6.17' for the shallower gradient section, and 1.31' and 5.23' for the steep section, respectively. Certified drawings showing the as -built plan and profile of the ditch were also submitted. The profile drawing shows generalized cross - sections for two legs of the ditch: the long, shallow leg which drains to the east; and the shorter, steeper leg which drains to the west. The cross section shows minimum depths and top widths of these legs of 2'6" and 12'3 ", and 2'0" and 8'3 ", respectively. The profile drawing shows the elevation at fewer survey points than were included on the original survey of October 8, 2013, which makes a direct comparison of the two surveys difficult. Although a new drawing with identical survey points would be helpful the Division recognizes that: • A fairly long section of the east leg of the ditch (from station 13) is almost level; its location and slope is constrained by the local geology • A field inspection of that leg does not reveal any areas of ponding water • The as -built depth and width of the ditch are each significantly greater than those specified by the SedCad design Office of Office of Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines