Transport of oil sands process-affected water from tailings sands to a constructed fen peatland

English Abstract:

Reclamation of the Athabasca oil sands region requires the reconstruction of fen peatlands in which mine waste materials (e.g.,petroleum coke and tailings sand) and salvaged reclamation materials (including peat) are commonly used. Tailings materials used to construct the upland areas that provides water to a constructed fen on the Suncor Energy lease have elevated concentrations of sodium (Na) and Naphthenic acids (NAs) being transported into the fen via a permeable layer beneath the peat. Peat (2 m thick) is expected to disperse and adsorp Na and NAs moving upwards through the peat profile. Water chemistry samples taken in 2013 and 2014 indicate the presence of Na and NAs at the base of the peat profile, and little in the rooting zone. For example, in 2013 Na concentrations averaged 314 mg/L in the upland (tailings sand) and 121 mg/L, 78.5 mg/L, and 87.3 mg/L in the fen peat at 150, 90, and 50 cm depths, respectively. In 2014, Na concentrations averaged 154.6 mg / L in the upland and 109 mg/L, 70.6 mg/L, and 82.1 mg/L in the fen at comparable depths, which indicates that Na present in the system was diluted. However, in 2013 NAs concentrations averaged 24.1 mg/L in the upland and 12.5 mg/L, 1.19 mg/L, and below detection in the fen at 150, 90, and 50 cm depths, respectively, generally increasing in 2014 to 26.8 mg/L in the upland and 11.1 mg/L, 5.47 mg/L, and 1.23 mg/L in the fen at comparable depths. The different behavior of Na versus NAs may be a result of NAs moving through “windows” faster than the mean rate; further assessment is required to understand this.The success of future reclaimed fen peatlands depend on designs accounting for the management of water quality. Further monitoring is required to characterize the rate of solute movement.