Effects of changing environmental rules: Kitsault molybdenum mine, Canada

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Abstract
The Kitsault mine was reopened briefly in 1981–82, after prior operations in 1967–72. Initial oceanographic assessments showed that a submarine tailings disposal (STD) system similar to that at Island Copper Mine would function to produce a tailings density current that would deposit on the fjord bed. There was substantial community interest and action during the final years of the development at a time when new pollution controls were being developed in Canada. The STD system essentially met its design criteria, but new oceanographic instrumentation at the time showed some contribution of tailings at the outfall discharge point to a naturally present mid‐water turbidity layer. The first intensive postclosure monitoring of ecosystem rehabilitation following STD use anywhere in the world was undertaken between 1983 and 1989. Soon after closure in 1983, pore waters in the submerged deposited tailings were observed to be enriched in molybdenum, which must have supported an efflux of the metal to the overlying water. The indicated flux would have been too small to have had a measureable effect on the Mo inventory in the deep waters and, furthermore, was predicted to diminish with time. The only detected biological impact was on the fiord benthos in the deposition area. Although benthos were present in the tailings deposits by 1983, there were differences between the tailings and nontailings areas. Some differences remained in 1986 and 1989. Great variability of the benthos in the reference area paralleled that in the tailings area.