2010-03-08_REPORT - M1977342 - Laserfiche WebLink

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J W. W. Wheeler and Assoc., Inc. Water Resources Engineers September 25, 2009 Mr. Curtis Brown Climax Molybdenum Company, Henderson Mill 19302 County Road 3 Parshall, CO 80468 Re: #1333.0 - Henderson Mill Spring Tailing Pond Survey Dear Curtis: We have completed our evaluation of the spring 2009 survey of the Henderson tailing impoundment. The survey of the beach area and the water pool was performed by Henderson surveyors in May, before spigot deposition began on No. 1 Dam. Figure 1 is the pond and beach contour map that was generated by Wheeler from the survey point and contour data. Note that the beach contours in the No. 3 Dam area had to be approximated since spigot deposition was taking place in this area and it was inaccessible to surveyors. As expected, the survey shows that the average dam crest elevation of No. 1 Dam at the time of the survey is similar to the elevation at the end of the spigot deposition season in 2008. This information, as well as other characteristics of the pond, is summarized in the table in the upper right-hand corner of Figure 1. Table 1 is the elevation-capacity table that was generated from the contour map. Note that this table is representative of the pond at the time of the pool survey and changes continuously as additional tailings are deposited. Figure 2 is a plot of the elevation-capacity data. The beach survey was performed prior to the construction of the deposition berm, which was constructed i n June. The material used to construct the deposition berm was borrowed from the beach area nea the dam crest. This practice effectively lowers the dam crest elevation, which we have defined as the beach elevation at the toe of the deposition berm. This lowering of the dam crest was accounted for in our analysis by using the beach elevation at 150 feet out from the berm as the modified crest elevation. This 3700 South Inca Street Englewood, Colorado 80110 Phone (303) 761-4130 Fox (303) 761-2802