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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 />COLORADO <br />D I V I S ION OF <br />RECLAMATION <br />MINING <br />SAFETY <br />MEMORANDUM John W. Hickenlooper <br />Governor <br />Mike King <br />Executive Director <br />Loretta Pineda <br />To: Wally Erickson Director <br />From: Tim Cazier, P.E. <br />Date: March 11, 2011 <br />Re: May Day & Idaho Mill Complex - General Portal Repair Comments, Permit <br />No. M-1981-185 / CN-01 <br />The May Day No. 1 Portal and the No. 3/Lamb Portal are in need of repair and/or stabilization. <br />The following comments are posed to ensure adequate engineering analyses and design practices <br />are implemented to eliminate or reduce to the extent practical the potential for additional collapse <br />or other slope failures that may pose a risk to the existing mill in order to protect all areas that <br />have the potential to be affected by designated chemicals, toxic or acid-forming materials in <br />accordance with Rule 6.4.21 (Designated Mining Operation Environmental Protection Plan). <br />Geotechnical Stability Exhibit (GSE), Rule 6.5: <br />1. On page 2 of the GSE, the application states, "There are no geologic hazards for slopes <br />greater than 1.5:1 on the May Day Idaho Mine Complex. Any slopes steeper than 1.5:1 <br />will be evaluated for stability." The Division cannot accept 1.5H:1 V slopes to be stable <br />without demonstration, especially given the first quarter, 2010 slope failure at May Day <br />No. 1 involving the collapsed portal discussed in the paragraph immediately below the <br />referenced quote. The Division will require a slope stability demonstration for any <br />facilities that are associated with slopes steeper than 2H:1 V and natural ground <br />disturbance. <br />2. In the last paragraph on page 2 of the GSE, there is a wide range for the allowable <br />bearing capacity of the soil (4,500 to 16,000 lbs/sgft). The applicant will need to <br />demonstrate the bearing capacity of the soil that will be supporting the steel sets. The <br />paragraph also suggests the soil being supported by the steel sets will be compacted (6 <br />feet of compacted soil for the 4,500 psf bearing capacity vs. 20 feet of compacted soil for <br />the 16,000 psf bearing capacity). If this is the intention, the work plan must indicate how <br />these supported soils will be compacted as well as how the load bearing soils will be <br />compacted. <br />3. On page 3 of the GSE (Highwalls), the application states, "Potential geologic hazards <br />will be evaluated once site access is granted..." This statement contradicts the statement <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines