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` ANdERSON CONSU~TINCt ENGINEERS, INC. <br />Civil Water Resources Environmental <br />November 18, 2005 <br />Mr. Terry McKee <br />Department of the Army <br />Corps of Engineers, Omaha District <br />Denver Regulatory Office <br />9307 South Wadsworth Blvd. <br />Littleton, CO 80128-6901 <br />RECEIVED <br />DEC 0 2 2005 <br />Division of Minerals ana Geology <br />Re: Durham Pit Long Term Flood Control Mitigation Plan - Review of Draft Construction Drawings. <br />Permit No. M-1978-056, Corps File No. 200380651. C/qsS I I~CViS%nh ~ C :Sc',~ t T-a. <br />[ACE Project No. COVC03-O1] U <br />Deaz Terry: <br />On behalf of the Varra Companies, Inc., Anderson Consulting Engineers; Inc. (ACE) is pleased to submit <br />the attached Long Term Flood Control Mitigation Plan (FCMP) for the Durham Pit. This Long Term <br />Flood Control Mitigation Plan is required as part of the State of Colorado Division of Minerals and <br />Geology (DMG) and Mined Land Reclamation Board's October 27, 2004 Findings of Fact, Conclusions of <br />Law and Order for the V arra Companies, Ina Mining Permit Amendment (See Attachment A). The Long <br />Term FCMP is required to minimize any potential adverse offsite impacts due to a 100-year flood event. <br />The FCMP consists of draft construction drawings as shown in Attachment B. As requested in the Corps <br />of Engineers' Mazch 30, 20041etter (See Attachment C) this material is being forwarded to you for your <br />review. <br />As shown in Attachment B, a spillway will be installed in a low area at the west end of the existing berm <br />on the right bank of the Cache la Poudre River. The spillway will be approximately 1270 feet long and <br />installed at an average elevation of 4921.5 feet. The spillway will allow a portion of the floodwaters in <br />excess of the 10-year flood event to exit the main channel and be conveyed in the right overbank. <br />Conveyance of flows through the post reclamation Durham Pit will occur in a manner similar to the pre- <br />mining condition. The spillway will consist of a 1-foot wide concrete control sill and a 20-foot wide <br />aggregate driving surface. Slopes landside of the spillway will be very gradual on the order of l OH: l V and <br />will require only vegetative erosion protection. The concrete sill will be protected from potential main <br />channel erosion by buried riprap revetment. Any areas disturbed during construction will be revegetated <br />with an appropriate seed mixture. <br />Irl July of 2005 the draft FCMP and associated Conditional Letter of Map Revision (CLOMR) was <br />reviewed by Weld County and forwarded to FEMA. It is estimated that the FEMA review will be <br />completed in approximately 1 to 2 months. As ofthe date ofthis letter, we have received no major review <br />comments from FEMA regarding the proposed project. <br />CO~'C03-01 TerreMcKee USAGE LTI-FM'.ALdoc <br />772 Whalers Way, Suite 200 ~ Fort Collins, CO. 80525 <br />Phone: (970) 226-0120 • Fax: (970) 226-0121 • www.acewatercom <br />