Red Dog Mine, Alaska
E & E has conducted two projects for the Red Dog Mine, the world’s largest zinc mine. Teck Cominco retained E & E to investigate matters concerning NPDES permit compliance for the mine’s treated reclaim wastewater (TRW) when previous, historical laboratory data obtained through use of the permit-specified analytical techniques exhibited high bias and outliers that precluded satisfactory compliance evaluation.
E & E’s performance evaluation addressed over 300 NPDES outfall samples and three laboratories performing total cyanide analyses. We determined matrix- and laboratory-specific method detection limits and identified associated NPDES interim minimum levels (MLs). We verified that significant matrix effects involving thiocyanate, iron, and other complex cyanide compounds were confounding determinations of permit compliance.
E & E’s variability analyses included examination of field and laboratory sample “fixing” techniques; investigation of chemical interferences; evaluation of weak acid dissociable (WAD) cyanide and free cyanide analytical methods; and quantification of the laboratory-specific, statistical concentration ranges for total cyanide in the TRW. The project team assessed the relevance of historically reported, apparent permit total cyanide violations with respect to matrix- and laboratory-specific MLs and demonstrated that the chemical interferences could not be overcome either in the field or in the laboratory.
To resolve the problem, we demonstrated that application of the WAD cyanide method to TRW samples would enable the client to meet NPDES permit requirements for an effective total cyanide method detection limit study.
We also developed and implemented sediment sampling plans associated with the Red Dog Mine NPDES outfall. The coarse, rocky composition of the stream beds and the scouring that occurs during the high flow events presents several challenges to the acquisition of sufficient sediment samples to enable for multicomponent analyses. E & E employed statistical multi-increment sampling to address these factors. In addition, we used a wet sieving bin the field to preclude coarse, nonsediment materials and to prevent deterioration of the cyanide and cyanide metal complexes that are the primary constituents of concern.