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(Woodward-ClyrJe <br />1Consultants <br />2.0 <br />PROJECT IhESCRIPTION <br />~- <br /> <br />The Henderson Mill is located along the Williams Fork River is Grand County, <br />Colorado, approximately 20 miles south of Parshall, Colorado. The mill part of Climax <br />Molybdenum Company's molybdenum operations was constructed during the eazly 1970s <br />and started operating in July 1976. From startup until December 1980, the mill had a <br />capacity of processing up to 30,000 tons per day of ore using three mills. In December <br />1980, the fourth mill came on line increasing the capacity to about 40,000 tons per day. <br />Tailing from the mill is slurried and moved by gravity though a pipeline to a tailing <br />storage azea at the outlet (eastern side) of the Ute Park basin. Storage is t~ehind Tailing <br />Dams 1, 2, and 3 constructed by the upstream method using header pipe and spigots <br />during the months April through October. Winter deposition in November through <br />March is by open-cnd lead-offs extending well into the storage area away :From the dam <br />crest. Dams 2 and 3 are auxiliary to Dam 1. Dam 1 will incorporate Dam 3, and Dam 2 <br />will be covered by tailings stored behind the single dam when Dam 1 is about 300 feet <br />high. The current planned height for the dam will be about 300 feet at crest Elevation <br />8900. The current height of Dam No. ] is approximately 170 feet at crest Elevation 8770 <br />with a crest length of approximately 7,000 feet, and on an overall slope of the tailing <br />portion of the embanl®ent of about 4.]:1 (horizontal to vertical). At crest Elevation <br />8900 the crest length will be about 11,000 feet and the storage capacity abourt 300 million <br />cubic yards. <br />The dam is an upstream method dam. Initially, a subdrain system was constructed <br />beneath the foundation of essentially the downstream slope of the dam. )It consists of <br />a series of perforated, corrugated metal pipes surrounded by drain gravels. A starter <br />dam, approximately 40 feet high, was constructed of native soils behind which tailing <br />deposition commenced. A decant system consisting of twin, steel pipes enveloped in <br />reinforced concrete extends through the dam toe into the reservoir area along the <br />southern side of the tailing disposal area. The dam is raised using atanda~•d upstream <br />method construction. A series of five instrumented study sections arc utilized to monitor <br />ns9va~.: osm-nivr 2-1 <br />