2010-01-06_PERMIT FILE - M2009082

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STATE OF COLORADO DIVISION OF RECLAMATION, MINING AND SAFETY Department of Natural Resources 1313 Sherman St., Room 215 Denver, Colorado 80203 Phone: (303) 866-3567 FAX: (303) 832-8106 January 6t", 2010 Jennifer Vecchi Vecchi & Associates, LLC P.O. Box 1175 Longmont, Colorado 80502-1175 COLORADO D I V I S I ON OF RECLAMATION MINING SAFETY Bill Ritter, Jr. Governor Harris D. Sherman Executive Director Ronald W. Cattany Division Director Natural Resource Trustee RE: Parsons Mine, DRMS File# M-2009-082; 112c Permit Application, Adequacy Review #2, Flood Mitigation. Dear Mrs. Vecchi, The Division has reviewed the information submitted in the permit application in regards to flood control structures proposed for the Parsons Mine. This specific section of the application was submitted with the Stability Exhibit, in the document entitled "Stability Analysis Parsons Project," under the section heading "Inflow and Outflow Structures." Please address the following concerns in regards to this section of the application: 1.) The Division has several concerns about the berms of unexcavated native material ground between several of the mining cells. These berms may erode and down cut during a flood. The potential for berms around gravel pits to be damaged during flooding is discussed in detail in the 1987 Urban Drainage and Flood Control District (UDFCD) Publication "Technical Review Guidelines for Gravel Mining Activities within or Adjacent to 100-year Floodplains." Strips of native ground or constructed fill between the stream and the gravel pit, and generally aligned with the flow direction of the stream are referred to in the UDFCD document as riverside berms. Strips of native ground or constructed fill between adjacent pits and generally perpendicular to the stream are referred to as lateral berms. Both riverside berms and lateral berms are proposed in the Parsons Mine application; both these berms may be prone to erosion during a flood event. The proposed inflow/outflow structures are intended to mitigate possible slope failure during flood events for these berms. The Parsons Mine is outside of the political boundaries of the UDFCD, but the technical floodplain factors that led to the formation of the UDFCD guidance still apply and were used to review the adequacy of the flood mitigation structures proposed for the site. There are lateral berms between mining cells 5A and 56, 4C and 413, 4C and 4A, and 4A and 4B. The minimum top widths between these berms is 130 feet according to the proposed mining and reclamation plan maps. UDFCD states that these berms can be left in a reclaimed but unimproved condition if the top widths for lateral berms is 250 feet. The current proposed plan calls for several inflow/outflow structures and culverts to be installed to mitigate erosion damage of these lateral berms. Office of Office of Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines