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,- i • <br />the mobile truck, and the lower cost. The routine application <br />of Coherex proved to be very effective minimizing airbos~ne dust, <br />In the mid 1980's magnesium chloride began to be widely used for <br />dust control on haul roads in open pit mining operations:. A <br />field test was conducted at the Henderson tailings impoundment <br />using magnesium chloride. The magnesium chloride did not work <br />well because of the low humidity and the lack of a "crus,t" being <br />formed. Therefore Coherex remained as the most effective means <br />of dust control. <br />By 1992, continued growth of the tailings impoundment meant that <br />the single spray truck required a more extended period of time to <br />completely cover the potential dust producing areas. In response <br />Henderson purchased a second spray truck at the cost of $190,000, <br />thereby doubling the application capability. <br />Industry research into state-of-art dust control methods during <br />1993, indicated that sub-aerial tailing deposition methods had <br />potential to control dust better than Coherex, and at a lower <br />cost. Knight-Piesold and Co. was contracted to design and <br />evaluate a field test of this method. The field test was <br />conducted in late 1993 on the south end of #1 dam. Final results <br />have not been received, however further test work is planned <br />during 1994, pending a successful recommendation from this work. <br />Soil covering has been employed on several of the dam face slopes <br />and benches to eliminate dust from these areas. This project <br />continues routinely. <br />Soil stockpiling for final reclamation has also been staged, by <br />the removal of the vegetative cover from only the areas <br />threatened by immediate inundation, and providing for immediate <br />reseeding of the storage stockpiles themselves thereby minimizing <br />dust generation from reclamation activities. <br />Mill policy has also been established to minimize any disturbance <br />in the tailing area, and to provide for rapid reclamation of any <br />necessary disturbance. An example of this was the construction <br />of the new tailing area interceptor ditch construction in 1991, <br />which was hydromulched immediately after completion. <br />Conclusion <br />The routine application of Coherex remains as the major :method of <br />dust control at the Henderson tailings impoundment. The <br />availability of two high flotation spray trucks, coupled with <br />mill management policy of rapid and thorough application ensure <br />effective dust control. Continued testing of sub-aerial <br />deposition or other methods yet unknown offer potential <br />improvement in dust control technology. Henderson remains <br />committed to providing effective dust control as a important part <br />of the milling process. <br />