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(Page 4) MINE ID / OR PROSPECTING ID f M-77-342 INSPECTION DATE 10-6-93 INSPECTOR'S INITIALS ACS been completed, indicating a high factor of safety for the impoundment. TYie operator should submit this analysis to the Division ae soon ae the material can be assembled. The submittal should include a hydrologic analysis which demonstrates that 10 feet of free-board is sufficient to prevent overtopping of the dam, given the upland diversions and the design storm event. Rational for selection of the design storm event should be included in the analysis. Several moderate wind gusts occurred during the inspection of the tailing impoundment that generated large duet plumes which carried tailing material generally down the valley. Duet generation from the tailing surface was noted in the 12/20/91 inspection report filed by Gregg Squire of the Division's staff, and by the Colorado Division of Wildlife during 1990. CLIMAX has recognized duet generation from the tails ae a potential problem at Henderson from the time of initial planning for the operation. AMAX conducted a study to determine the beet method of controlling fugitive duet from tailing deposition areas at the Climax Mine in 1970. This study identified Coherex, an asphalt-water emulsion, ae the best euppreeeion agent. The 1970 study indicated that Climax was continuing research in the area of fugitive duet euppreeeion. Climax initiated an ecological monitoring program in the areas surrounding the mill and tailing disposal facilities prior to start up of operations ac the site. The monitoring program was designed, in part, to detect impacts caused by fugitive dust from the tailing surface. The program included monitoring of climate, vegetation; soil chemistry, large mammal utilization, watershed biology, ae well ae surface water and ai.r quality. There ie very little data from the monitoring program contained within the Division's partial files for the operation; if monitoring data ie not forthcoming ae part of the permit file copying and submittal process discussed earlier in this report, the operator a?could prepare and submit the available information. The submittal should include an aseea:3ment of the data which focusses on the impacts of fugitive duet from the tailing. The difficulty in controlling duet from the Henderson tailings at certain times of the year, ie that the duet suppression agent is applied by trucks, and there ie a band of tailing surface that lies between wet tailing, with no duet generation problems, and dry tailing where Coherex has been applied. This band consists of tailing with a dry surface layer, and attendant dust generation, underlain by saturated tails that are :not sufficiently consolidated to support the Coherex truck. in a letter dated January 9, 1992, from Jay Jones, Henderson Environmental Manager, to Gregg Squire, Division staff, .it ie stated: Ae the impoundment area has grown, so has the need far more effective control of fugitive duet emissions. At this time, technical and operating parameters ouch ae the operation of the 'drips', the late season application of Coherex and the amount of beach necessary for dam stability are being re-evaluated by the Mill operations department:. Additionally, the Mill engineering group ie evaluating alternative means of dust suppressant application and alternative duet control p.roducte. We are confident that these efforts will prove effective ire minimizing our fugitive duet emissions. The operator ie referred to C.R.S. 34-32-116(7)(1) which states: All surface areas of the affected land, including spoil piles, shall be stabilized and protected eo ae to effectively control erosion and attendant air and water pollution. The Division believes that it is incumbent upon the operator to employ best available technology to control wind erosion of the tailing, and that the erosion control measures be diligently applied. To this end, the operator should supply the Division with a list of refinements to the CLIMAX dust control program that have been implemented since the 1970 study, ae well ae an update of the on-going duet control research referenced in the 1970 report and in the 1/9/92 letter. It was apparent during the inspection that the dust control program at Henderson, as it currently exists, ie being diligently applied, however, the required submittals are needed to assure the Division that the current program represents best available technology.