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Twentymile Coal, LLC. <br />Page 6 <br />April 3, 2015 <br />27. On revised page 2.05- 191.9, the applicant indicates subsidence monitoring will be conducted at <br />the railroad. A trigger has been specified when monitoring will be initiated for this structure, but <br />a frequency of monitoring (daily, weekly, monthly... etc.) is not specified. Please revise this <br />section to indicate the frequency the railroad will be monitored. <br />28. Revised page 2.05 - 184.11 indicates mining of the WCR will result in undermining and subsiding <br />the Yampa Valley Electric Line serving the mine. Exhibit 7K submitted with PR10 indicates that <br />three powerlines will be impacted by subsidence. Please update page 2.05- 184.11 to discuss all <br />three powerlines that will be impacted by mining of the WCR. <br />29. As indicated in the previous item, Exhibit 7K indicates mining and subsidence will impact three <br />powerlines. The monitoring plan for the powerlines discussed on revised page 2.05 -191.9 only <br />discusses the Yampa Valley Electric Line. Please revise this section to discuss all three <br />powerlines. <br />30. In the NW I/4 of Section 13, T5N R86 West, a very steep slope with potential rock outcrops is <br />located above RCR33. Subsidence from the east end of the WC -5RT panel will impact this area. <br />Please evaluate the danger of rock fall caused by the subsidence of this slope and its potential <br />impact to motorists on RCR33. Please revise the subsidence control plan to address this issue. <br />Other <br />31. The Division received three comment letters. The Colorado Division of Water Resources <br />submitted a letter dated March 2, 2015. History Colorado submitted a letter dated February 10, <br />2015. The Office of Surface Mining submitted a letter dated March 17, 2015. These letters are <br />enclosed for your review. <br />This concludes the Division's preliminary adequacy review. If you have any questions feel free to <br />contact me at (303) 866 -3567, extension 8120. <br />Sincerely, <br />Jared Ebert <br />Environmental Protection Specialist <br />Enclosures: <br />1. The Colorado Division of Water Resources letter dated March 2, 2015. <br />2. History Colorado letter dated February 10, 2015. <br />3. The Office of Surface Mining letter dated March 17, 2015. <br />