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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 />August 5, 2013 <br />J.C. York <br />J &T Consulting, Inc. <br />305 Denver Avenue, Suite D <br />Fort Lupton, CO 80621 <br />Re: Loloff Construction, Inc., Loloff Mine, Permit No. M- 1985 -112 <br />Technical Revision No. 1(TR -01) Adequacy Review - Hydrology <br />Mr. York: <br />COLORADO <br />D I V I S I ON OF <br />RECLAMATION <br />MINING <br />— St— <br />SAFETY <br />John Hickenlooper <br />Governor <br />Mike King <br />Executive Director <br />Loretta Piheda <br />Director <br />The Division of Reclamation, Mining and Safety (Division) has reviewed the hydraulic analysis of <br />the Loloff Construction, Inc. technical revision submittal for the Loloff Mine and submits the <br />following comments. The Division is required to make an approval or denial decision no later <br />than September 1, 2013 therefore; a response to the following adequacy review concerns <br />should be submitted to the Division as soon as possible. <br />1. The methodology uses "equilibrium well equations" from Driscoll. The application is for a <br />pit with a 600 -foot radius. Please provide additional justification for the use of well <br />equations for a very large (pit) opening. <br />2. The selected hydraulic conductivity appears to fall into a reasonable range for gravel pit <br />material (clean sand K can range between 100 and 60,000 gal /day /sq -ft). However, the <br />method used is extremely sensitive to this parameter. A quick check using your <br />methodology indicates increasing K to just 1,500 (still well within the range for clean sand) <br />increases the radius of influence by more than 1,000 ft. Please provide justification for the <br />selected hydraulic conductivity or use a value that can be justified. <br />3. The Division does not follow the logic in case 2 for reducing the hydraulic conductivity 33% <br />to account for the recharge being 33% of the pumping rate. Please elaborate on this <br />assumption. <br />4. Please replace the calculation of aquifer drawdown from pit pumping with a <br />calculation using the method described by Marinelli and Nappoli, 2000 (Ground Water, vol. <br />38, no. 2). Please include calculations for the maximum radius of influence and the <br />expected drawdown at a horizontal distance of 800 feet outside the west side of the pit <br />The method described in your submittal does not appear to adequately account for aquifer <br />recharge. Figure 7 of Arnold et al, 2003 (USGS Water Resources Investigations Report 02- <br />467) indicates drawdown at the 800 -foot distance would be approximately 10 feet. <br />Office of Office of <br />Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive <br />Mines <br />