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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 />3 June 2009 <br />Mr. Ryan Pawlowski <br />Colowyo Coal Company, LP <br />5731 State Highway 13 <br />Meeker, CO 81641 <br />Re: Colowyo Mine C-1981-019 <br />Third Adequacy Review - Technical Revision 73 <br />Dear Mr. Pawlowski: <br />COLORADO <br />D I V I S 10 N O F <br />RECLAMATION <br />MINING <br />SAFETY <br />Bill Ritter, Jr. <br />Governor <br />Harris D. Sherman <br />Executive Director <br />Ronald W. Cattany <br />Division Director <br />Natural Resource Trustee <br />The Colorado Division of Reclamation, Mining and Safety (Division) has received the <br />Colowyo Coal Company, LP (Colowyo) responses to Technical Revision 73 - changes to <br />the hydrologic curve numbers for sediment pond design, dated 11 May 2009. The <br />responses were received by the Division on 18 May 2009. The Division has reviewed the <br />responses and has the following adequacy questions. <br />Response Accepted. <br />2. Colowyo has modified curve numbers in Table 1 of the Methodologies and <br />Assumptions section of Exhibit 7 (page 3). As explained in the text, section <br />1.8, curve numbers for future hydrology and sedimentology calculations will <br />be as presented in the last column heading "curve number current". One <br />noted change was a lowering of the curve number for "disturbed, topsoil <br />stripped" from a value of 91 to 85. Based on the historic operational practice <br />at the Colowyo Mine, much of the disturbed area drains to the mining pit and <br />is not considered in the hydrologic calculations as part of the watershed area <br />draining to a pond or structure. Should large areas of topsoil stripped lands <br />not drain to an active pit, the Division anticipates Colowyo would use <br />conservative design assumptions to account for the large volume of storm <br />runoff that would be anticipated from lands in this condition. The Division <br />has no further questions regarding the curve number values proposed. <br />Colowyo states that no A soils exist in the area and B and D soils are rare, <br />which is supported by baseline soil mapping and NRCS information available. <br />The Campspass soil is a B soil, and if rare at the site, should not be used in the <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines