2014-10-06_REVISION - C2010089 (3)

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1313 Sherman Street, Room 215 Denver, CO 80203 October 6, 2014 Chris Gilbreath Tri-State Generation and Transmission Association, Inc. P.O. Box 33695 Denver, CO 80233-0695 Re: New Horizon North Mine (Permit No. C-2010-089), TR-07, adequacy letter Dear Mr. Gilbreath: We received your submittal of TR-07 on September 4, 2014. The Division understands that TR-07 was submitted to meet an abatement requirement of violation CV-2014-004. This violation was written by the Division because the as-built documentation does not accurately replicate observed ground conditions regarding the construction of the NHN-001 East and West Ditches. In the Settlement Agreement between Western Fuels – Colorado and the Division (the result of an Assessment conference on August 7, 2014) the abatement entailed two options:  Reconstruction of the ditches to put them in compliance with the designs in the New Horizon North permit application package, or  Obtain approval of a technical revision revising the designs to conform to the on-the-ground construction of these ditches. The Division further understands that TR-07 was submitted to meet the second of these two requirements. We have the following adequacy issues with the TR-07 submittal. 1. We have reviewed the submittal and looked at the conditions of the channels and find that there are significant discrepancies between the designs and the actual ditches. The most glaring of these discrepancies is Segment 2 of the West Ditch. It is designed to be triangular channel, however field observations (for example, see my inspection report from August 28, 2014) reveal that it is a very wide trapezoidal channel. Also, it appears that Segment 7 of the East Ditch may not be as deep as necessary to meet the designed cross-sectional area of 7.2 square feet; Division calculations suggest that the depth should be 18 inches or more, but field observation showed that the depth is closer to 14 inches. Please address the design of Segment 2 (West Ditch) and check the actual and required depth for Segment 7 (East Ditch). Also, please make sure that the entire design conforms to the on- the-ground conditions of the two ditches. 2. Map 2.05.3(4)-7 shows an EPDM liner at the steep portion where the channel meets the pond. However, Table 2.05.3(4)-7-1indicates that half culverts are used on these steep slopes. The half culvert was also seen in the field. Please revise the map or clarify this potential discrepancy. 3. The drainage areas and topography on Map 2.05.3(4)-7 are somewhat confusing. Some of the 1313 Sherman Street, Room 215, Denver, CO 80203P 303.866.3567 F 303.832.8106 http://mining.state.co.us John W. Hickenlooper, Governor | Mike King, Executive Director | Virginia Brannon, Director