Hydrochemical and stable isotope assessment of tailings pond leakage, Nickel Plate Mine, British Columbia

An integrated hydrogeochemical and stable isotope study was undertaken to assess tailings pond leakage at the Nickel Plate Mine site in British Columbia, Canada. The approach used consisted of a hydrochemical mixing model for sulfate in conjunction with stable isotope data (180 and 2H) to estimate possible levels of contamination reaching surface waters from leakage through the dam and to determine the relative percentages of seepage that can be attributed to leakage through the dam and to natural groundwater flow beneath and around the dam. Results suggest that tailings pond waters are diluted by groundwaters by approximately 50% before their arrival in the collection swamps, and that the leakage from the tailings pond partially by-pass the collection (and pump-back) system at a rate of between 0.09 and 0.12 1/s. Stable isotope data indicate that tailings pond waters and swamp waters are enriched in the heavier isotopes as a result of evaporation, and thus, tend to plot along an evaporation line of slope 3.9 (D/180). The isotope data indicate that seepage beneath the dam consists of approximately 50% real seepage and 50% meteoric waters (both surface water and groundwaters).