Laserfiche WebLink
<br />Memo to Larrv Oehler 5 May 5 1994 <br />concentrations in excess of permit limitations to be "high cyanide", <br />and at this time, all cyanide data on flows to the collection pond that <br />the Division has received exceed permit limitations. There is also the <br />consideration of the amount of dilution that takes place before the <br />interstitial water exiting the tails at the tailing-drainage layer <br />interface arrives at the outlet pipe to the collection pond. This <br />dilution is from storm water that enters the impoundment and reports <br />directly to the drainage layer, and from water reporting to the <br />drainage layer as a result of dewatering the west pit. Ttie influx of <br />INCO treated slurry into the impoundment should be beneficial in <br />partially flushing the AVR tails, but this process would not be <br />anywhere near complete by the time the end of the projected life of the <br />impoundment is reached. <br />Conclusion <br />The Division is not currently satisfied that the AVR tail:, the Cytox <br />tails, the Hz02 tails, or even the INCO tails, as well as their <br />associated interstitial fluids, are benign from either a cyanide or a <br />metals generation stand-point, and is not convinced by qualitative <br />arguments regarding "natural" cyanide destruction processes that <br />seepage from the impoundment, if it were to reach the water table, <br />would not significantly degrade the aquifer. There is tangible reason <br />to believe that excessive hydrostatic head is being app:Lied to the <br />tailing facility composite liner in areas beneath the free water ponds. <br />As was indicated in the Sorenson to Humphries memo dated June 24, 1992, <br />the chief factor in limiting seepage through a composite liner <br />installed with excellent QA/QC, is the ability of a drainage layer to <br />minimize head applied to the liner. Since excessive head applied to <br />the liner greatly increases the risk of excessive seepage through the <br />liner, BMRI should be required to install angled monit~~ring wells <br />beneath the impoundment in order to determine if the specific retention <br />of the subsoils has been exceeded, and if a contaminant plume is <br />migrating toward the water table. <br />cc: Jim Stevens <br />Bruce Humphries <br />C:\WP51\8MRI1 <br />