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INTRODUCTION <br />The purpose of this report is to present the results of our evaluation of the hydrologic <br />characteristics of the tailing storage facilities at the Henderson Mill and the effects of <br />eliminating the existing tailing pond spillway system. Elimination of that spillway system <br />would be associated with the proposed Barge Pumping System project. The Henderson Mill <br />is a molybdenum processing facility owned and operated by Climax Molybdenum Company <br />(Climax) that is located in Grand County approximately 13 miles north of Silverthorne, <br />Colorado. The mill is located along Ute Creek, a tributary of the Williams Fork River. The <br />Henderson Mill is a "zero discharge" facility, meaning that all of the water diverted into the <br />system is used until it is fully consumed. Under all but extreme conditions, no water is <br />released from the system. <br />The flood control systems at the Henderson Mill consist of two levels of protection. <br />The first level involves the bypass of flows resulting from snowmelt floods and rain floods of <br />Tess than a 100 -year retum period. This bypass is provided by a complex system of pipelines <br />and canals that deliver the flows around or through the mill facilities to the Williams Fork <br />River. This same bypass system is used to intercept and bypass normal runoff flows from <br />the tributary basins above the mill to the river below. <br />An integral part of the bypass system at the mill is the interceptor canal that extends <br />from Ute Creek around the west side of the tailing pond. The purpose of this interceptor is to <br />bypass fresh water around the impoundment into Ute Creek below the tailings dam. As the <br />water level in the tailing pond continues to rise, it will eventually be necessary to relocate this <br />canal. <br />The second level of flood protection at the mill relates to the ability of the system to <br />withstand the effects of a probable maximum precipitation (PMP) event. The design and <br />configuration of the mill facilities require that floods resulting from a PMP event (probable <br />maximum flood or PMF) are safely stored in the tailing impoundment, and in the two <br />reservoirs when storage space is available. With the existing system, the flood flows would <br />then be released from the tailing impoundment through the spillway /decant system. <br />1 <br />