2009-09-25_PERMIT FILE - M2009076 (22)

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face. The drain ends shall be connected and piped with solid 4" plastic pipe to the wet sump of the leachate collection and recycle system. Geotextile shall be pinned to the exposed surface face to minimize wind and/or stormwater erosion on a .as-needed basis. This will be done until permanent stabilization through revegetation and/or rip rap can be installed. Permanent control measures will be installed in 10 feet phased increments (elevation height of one quarter of a terrace or bench) which is estimated to occur every several months. This consists of covering the impoundment area with a 4" blend of Class-A municipal bio-solids and wood chips. A geo-textile or jute netting will then be applied to prevent water and wind erosion. This application will augment the deposited solids for the establishment of soil capable of supporting re-vegetation. A highland pasture grass seed suitable for mountain altitudes will be sowed together with fertilization and irrigation until permanent vegetation is re-established. This method of reclamation was successfully implemented by Phelps Dodge at the Climax Mine as referenced in Exhibit D. It should be further noted that the USFS has an ongoing pine beetle kill remediation project and the availability of wood chips will not only be massive, but using this material will help the local community dispose of this "waste" product. Additionally, as each 40' high terrace is completed, the surface of the terrace will be re-vegetated as described above. Rip-rap will be installed for a channel width of 6 feet at each end of the impoundment, at the intersection with the natural grade, to provide a permanent stormwater control. The existence of a natural diversion channel will also be acceptable for stormwater diversion as is found near the bottom half of the impoundment area. This natural channel is incorporated into the sedimentation pond. More reclamation details are to be found in Exhibit D and within the maps and drawings of Exhibit E. Specific details about the Tailings Impoundment Structures can be found above in 633(1)(e). • 6.3.3(2)(c) Drainage control within the Tailings Impoundment Affected Area has been considered using the U.S. Soil Conservation Service, Technical Release 55: Urban Hydrology for Small Watersheds, USDA (U.S. Department of Agriculture), June 1986 for design guidance. Additionally, the USDA Natural Resources Conservation Service has published software for analysis of systems covered by the Technical Release 55. The up-gradient native watershed from the Tailings Impoundment was analyzed using the following assumptions: • Drainage area of approximately 40 acres • "Group A" soil classification (sand, sandy loam), a higher degree of rainwater infiltration >0.3 in/hr. • Run Off Curve number, weighted = 48, representing a meager rangeland (50-75% cover) with moderate brush and minimal forestation. • An average slope of 0.6 ft/ft. The watershed of the affected Tailings Impoundment was analyzed using the following assumptions: • Drainage area of approximately 8 acres, total buildout considered with phased reclamation • "Group C" soil classification (sandy clay), a moderately low degree of rainwater infiltration at 0.05-0.15 in/hr. • Run Off Curve number, weighted = 74, representing a meager rangeland (50-75% cover) with minimal brush and no immediate forestation. • An average slope of 0.6 ft/ft. on embankment faces. As reported by NOAA's Atlas 2 Vol. III precipitation maps for Colorado, the following data is relevant for this site: • 100 year/24-hour precipitation= 3.8" or 0.158"/hr., Type II distribution • 10 year/24-hour precipitation= 2.6" or 0.108"/hr., Type II distribution A 100 year/24-hour event will produce the following Peak Discharge and Runoff at the Tailings Impoundment storm management structures: • • Peak Discharge within the diversion ditches = +/- 4.59 cfs (2,060 gpm). Each side of the complex will receive one half of this flow. 16