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• Description of Best Management Practices (BMP's) <br />The most significant source of potential stormwater contamination results from the pre-existing, historic <br />and abandoned waste rock on site. This has been a problem for well over 100 years. This operation will <br />be re-processing this waste to remove pollutant sources and impound the new waste in a carefully regulated <br />manner. <br />As part of newly proposed operations, BMP's have been developed to minimize impacts from the historic <br />waste piles on a phased approach as a new zone is disturbed. The new milling operations and subsequent <br />new tailings disposal will also have individual BMW's developed. For a complete understanding of the <br />mining operation, please refer to our DBMS permit work under M-2009-076. All SWMP components are <br />illustrated on the maps included in Section 3. <br />Stormwater Diversion: <br />o Pre-Existing Waste Rock/New Tailings Impoundment: There will be several <br />structural BMW's employed to divert stormwater run-off from coming in contact with the <br />previously described pre-existing waste rock and the new lined Tailings Impoundment. <br />Per DRMS regulations, this system must be designed to safely pass a 100 year/24-hour <br />storm event. As reported by NOANs Atlas 2 Vol. III precipitation maps for Colorado, <br />the following data is relevant for this site: 100 year/24-hour precipitation = 3.8" or <br />0.158"/hr., Type II distribution. <br />¦ A perimeter diversion ditch will be incrementally built to divert stormwater run- <br />off from the pre-existing waste rock as it is disturbed. Rip-rap will be installed <br />for a channel width of 6 feet and depth of a least 2 feet (open trapezoid cross- <br />section) at each end of the impoundment benches, at the intersection with the <br />natural grade, to provide a permanent stormwater control. This will be <br />constructed in phases as the impoundment expands. The existence of a natural <br />diversion channel with similar dimensions will also be acceptable for <br />• stormwater diversion as is found near the bottom half of the impoundment area. <br />This natural channel is incorporated into the Sedimentation Pond. <br />o Water Holding Pond: A small pond will be constructed with an average size of 4' deep <br />x 6' wide x 100' long and can store 15,000 gallons of mill feed water. Upon <br />recommendations by the DRMS, a 60 mil textured HDPE liner will be installed prior to <br />operations. This liner will be assembled from 22.5' wide material that will be field <br />fabricated. The seams will be made with a fusion machine. New water and recycled <br />process water from the leachate collection .system is contained here for milling <br />operations. Sand bags will be stacked on the uphill side to divert the small amount of <br />stormwater that may run-off in this area. A minimum of 6" of freeboard shall be <br />maintained so that a 100 year/24-hour rainfall event can be adequately contained. A <br />Temporary Substitution Water Plan is in place to purchase substitution water to offset <br />water that becomes co-mingled with process water. <br />o Tailings Impoundment/Pond: As the tailings impoundment embankment is constructed <br />with the coarse fraction of the slurried tailings, a pond is created containing process <br />water. This process water will be decanted and recycled back to the Water Holding Pond. <br />A minimum of 12" of freeboard shall be maintained so that a 100 year/24-hour rainfall <br />event can be adequately contained. A Temporary Substitution Water Plan is in place to <br />purchase substitution water to offset water that becomes co-mingled with process water. <br />Materials Handling and Spill Prevention: There will be several structural BMP's employed to <br />isolate feedstock and chemicals. Additionally, several non-structural techniques will also be <br />implemented. <br />o Crusher Feed Pad: This is the unloading station. A 30' x 32' concrete pad, sheltered <br />with a roof and sides, will be constricted to keep intermediate ore/waste rock isolated <br />from storm events. The concrete will keep any inherent moisture from leaching out onto <br />the ground. The surrounding grade will be sloped to divert run-off waters from entering <br />• this area. Operators will be instructed that if material is spilled, that it should be re- <br />collected and re-fed into the process stream. <br />Page 5 of 10