2009-03-16_REVISION - C1981019 - Laserfiche WebLink

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STATE OF COLORADO 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 16 March 2009 Mr. Ryan Pawlowski Colowyo Coal Company, LP 5731 State Highway 13 Meeker, CO 81641 Re: Colowyo Mine C-1981-019 Second Adequacy Review - Technical Revision 73 Dear Mr. Pawlowski: COLORADO D I V I S I O N O F RECLAMATION MINING SAFETY Bill Ritter, Jr. Governor Harris D. Sherman Executive Director Ronald W. Cattany Division Director Natural Resource Trustee The Division of Reclamation, Mining and Safety (Division) has received Colowyo Coal Company's (Colowyo) responses to Technical Revision 73 - changes to the hydrologic curve numbers for sediment pond design, dated 2 March 2009. The responses were received by the Division on 4 March 2009. The Division has reviewed the responses and has the following adequacy questions. Response Accepted. 2. The Division does not agree with some of the SCS curve number ranges as presented in Table 1 (Exhibit 7, page 3) for the following two reasons. a. Hydrologic soil groups are represented in Table 1 as B soils for all reclaimed lands (topsoiled areas post-reclamation). According to information provided on page 4, Exhibit 7, the Campass, Bumette, and Work Series soils are the three dominant soils within the proposed disturbed area. The Burnette and Work series are C soils (reference TR-55, Second Edition, June 1985, Exhibit A-1, Hydrologic soil groups for US soils). Given that soils will likely experience some compaction during re-application, representing all soils as being in the C category would likely result in more accurate storm runoff modeling. Please use accurate soils information. b. No site-specific evidence in the form of vegetation sampling results for total cover was provided to justify 85% cover on areas of 1-2 years growth or the 3+ year growth areas. Please provide support for the amount of hydrologic cover based on the annual vegetation surveys of the reclaimed area. The Division noted a discrepancy between Table 6 and the narrative in Section 1.9. Section 1.9 Base Flow, of the revised materials states "A base flow of 0.15 cfs was used for the Streeter Pond design. A base flow of 0.03 cfs was used for the West Pit pond design. Base flows were not used in any other pond design." Table 6 shows three ponds with a base flow. Second, Colowyo deleted the statement in Section 1.9 that said, "Discharge of collected water from the open pits, as a result of pumping, will not be permitted during a storm event equal to or greater than the 10-year, 24-hour storm event". In our 12 June 2008 letter we asked that Office of Office of Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines