DISTRIBUTION OF METALS AND METALLOIDS IN AQUIFERS IMPACTED BY THE INGRESS OF PROCESS-AFFECTED WATER FROM OIL SANDS TAILINGS

The mining of oil sands deposits in Northern Alberta produces large amounts of tailings containing process-affected (PA) water. Tailings impoundments are generally located over low permeability glacial tills; however, in some cases, the glacial tills contain paleochannels, which may provide an avenue for PA water migration from the tailings deposits. As part of a larger study, the effect of PA water ingress on metal speciation, redox state, and mobilization is investigated. To assess metal release under field conditions, a small injection of PA water has been performed in the Wood Creek Sand Channel (WCSC) aquifer located adjacent to an existing tailings facility. Groundwater data collected prior to PA water injection indicate that the natural aquifer conditions are mildly anaerobic and that trace metal concentrations are low. Following PA water injection, the concentrations of Sr, Ba, Zn, Co, Mn and Fe increased above background levels. It is possible that microbially mediated reductive dissolution of metal oxides/oxyhydroxides hosting trace elements is releasing Sr, Ba, Zn, Co, Fe(II) and Mn(II) into solution. However, solid phase speciation data is needed to understand the processes that lead to the observed increase in dissolved metal concentrations. Core samples were collected from within the WCSC aquifer prior to PA water injection. Characterization of the core samples, by employing a previously established sequential extraction procedure (SEP), will elucidate the natural partitioning of environmentally relevant elements within the WCSC. Based on the groundwater data, sediment samples were subjected to a SEP to evaluate the partitioning of fifteen trace elements (Fe, Mn, Al, Zn, Cu, Ag, Ni, Co, Sr, Ba, Cd, Sb, Pb, V, and Cr). The distribution and possible mechanisms affecting the mobility of inorganic contaminants of concern in the WCSC will be addressed.