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= ~ ` - e~ III IIII111111111111 <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Natural Resources <br />1313 Sherman $I., Room 215 <br />Denver, Colorado 80203 <br />Phone: !7031866-3567 <br />FAX: (703)832-8106 <br />Date: November 7, 1994 <br />To: Randy Price <br />From: David Berry <br />Re: Technical Revision No. 12 - Phase I Bond Release Issues <br />Mari Mine, Permit No. C-80-006 <br />~I~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Wvernor <br />lames 5. Lxhhead <br />EKrculive Drretlor <br />Michael B Long <br />Division Director <br />As requested, I have reviewed the above-referenced submittal with regard to items numbered 6 <br />and 7 of our May 25, 1994 correspondence. My comments follow: <br />1. Pond A may be oversized; however, design adequacy is difficult to assess with the currently <br />submitted information. Possible problems are as follows: <br />- The revised page 23-19R indicates a pond volume of 18.40 acre-feet, but Prate 1, <br />Exhibit 29, seems to indicate a volume of only 13.98. Please clarify. <br />- My calculated 25-year, 24-hour peak flow is about 160 cubic feet per second (cfs), which <br />is close to the operator's projected 25-year, 24-hour peak flow projection of 159 cfs. <br />However, the operator's proposal uses a 2.4-inch 25-year, 24-hour rainfall for the <br />SEDCAD input. <br />- My calculations result in a higher 10-year, 24-hour nunoff volume and peak flow than are <br />presented in this submittal. Our calculated 10-year, 24-hour runoff is about 16 acre-feet. <br />This seems to indicate that Pond A may now be undersized. The difference may be <br />resolved by addressing the issues listed below. <br />- The operator might want to verify that the Canadian area actually drains to Pond A. If <br />some or all of this area can be eliminated as contributing area, Pond A inflow calculations <br />can be reduced. <br />- The actual routing pattern used by the operator for the purpose of SEDCAD modelling is <br />not clear. Please have the operator submit a map or figure which clearly defines the <br />routing designations. This should correlate with current topography and ditch location. <br />- The curve number of 69 seems low. The soils in the area are generally Hydrologic <br />Group C or D (Coahnont, Barishman, Asberg). Reclaimed areas can be considered <br />