δ98MO FINGERPRINTING OF ATHABASCA OIL SANDS PROCESS AFFECTED WATERS

The release of oil sands tailings process affected waters (OSPW) to the natural environment is a concern for both aquatic ecosystems and the health of human receptors in downstream communities. Tracers capable of identifying the transport of OSPW through processes such as atmospheric deposition and release from tailings ponds are critical to quantifying the risk to humans and the environment. In a recent study, it was determined that molybdenum (Mo) concentrations in OSPW were one to two orders of magnitude higher than concentrations in natural waters in the Athabasca Oil Sands Region (AOSR). The elevated concentrations of Mo in OSPW provide an opportunity for δ⁹⁸Mo isotopic fingerprinting, which has until recently been a challenge due to the relatively heavy mass of Mo isotopes and low concentrations of Mo in natural waters. In this study, Mo isotope ratios from anthropogenic waters (coarse tailings, tailings ponds and SAGD steam condensate) and natural waters (Athabasca River, Quaternary aquifers, McMurray and Devonian Formations) from the AOSR were analyzed to determine the range of isotopic signatures in the region and assess the suitability of δ⁹⁸Mo as a tracer. δ⁹⁸Mo values in coarse tailings and steam condensate were found to be isotopically distinct from natural waters suggesting δ⁹⁸Mo could serve as a useful tracer for OSPW. However, δ⁹⁸Mo within tailings pond waters demonstrated a signature similar to natural groundwater from the Quaternary aquifers and McMurray Formation. The difference in δ⁹⁸Mo values in the coarse tailings at the point of discharge into the pond and the values measured within the pond are consistent with fractionation due to the formation of iron or manganese oxides, or biological processes favouring the assimilation of lighter Mo isotopes.