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current alignment for storm events up to the 100-year, 24-hour event. Such designs would <br />require that the application be amended to include all portions of the river channel to be <br />stabilized. DMG would require such stabilization work to be completed prior to commencement <br />of the proposed excavation activity. <br />2. The application anticipates that the low-lying portions of the pit area will flood each spring <br />during high runoff periods. Under such a scenario, the proposed mining activity has potential for <br />off-site damage and adverse impact to the adjacent river channel by head cut, tail cut and lateral <br />erosion occurring as the 15-foot deep pit refills with sediment eroded from the immediately <br />surrounding areas. The proposed vegetative cover, composed of willow transplants and <br />grasses, will be applied only after mining has been completed. Therefore, the application does <br />not appear to address control of such erosion during the life of the mine. Additionally, the <br />application does not demonstrate that the proposed vegetative cover will be sufficient to <br />stabilize reclaimed areas against such erosion after completion of reclamation. Pursuant to <br />Rules 3.1.5(3), 3.1.6(1) and 6.3.3(1), DMG recommends that the application include engineered <br />designs for pit inlet and outlet structures, as well as armoring the perimeter of the pit, similar to <br />those provided in the Urban Drainage & Flood Control District manual, certifying stability of the <br />affected lands for storm events up to the 100-year, 24-hour event. <br />Please find enclosed, copy of DMG's In-Stream Aggregate Extraction and Reclamation <br />Guidance Document, also available on DMG's web site at www.mininq.state.co.us. <br />Please find enclosed, staff memo from Dr. Harry Posey, dated December 21, 2005, regarding <br />the potential for release of acid-toxic substances from the proposed gravel operation. <br />If more time is required to satisfy these adequacy issues please request an extension to the <br />decision date prior to January 9, 2006. <br />Please contact me at the DMG Durango Office, 701 Camino del Rio, Room 125, Durango, CO <br />81301, phone (970) 247-5469, if you have any questions. <br />Sincer y, -~ `G~., ~n <br />Wallace H. Erickson <br />Environmental Protection Specialist <br />Enclosure: DMG's In-Stream Aggregate Extraction and Reclamation Guidance Document, 8/98 <br />cc w/enclosure: Jack Clark, Jr. <br />cc w/o enclosure: Kara Hellige, Durango Regulatory Office, US Army Corps of Engineers <br />Harry Posey <br />AIIen Sorenson <br />