Formation waters discharge to rivers near oil sands projects

Abstract

Groundwater discharges in the western Canadian oil sands region impact river water quality. Mapping groundwater discharges to rivers in the oil sands region is important to target water quality monitoring efforts and to ensure injected wastewater and steam remain sequestered rather than eventually resurfacing. Saline springs composed of Pleistocene‐aged glacial meltwater exist in the region, but their spatial distribution has not been mapped comprehensively. Here we show that formation waters discharge into 3 major rivers as they flow through the Athabasca Oil Sands Region adjacent to many active oil sands projects. These discharges increase river chloride concentrations from river headwaters to downstream reaches by factors of ~23 in the Christina River, ~4 in the Clearwater River, and ~5 in the Athabasca River. Our survey provides further evidence for the substantial impact of formation water discharges on river water quality, even though they comprise less than ~2% of total streamflow. Geochemical evidence supporting formation water discharges as the leading control on river salinity include increases in river chloride concentrations, Na/(Na + Ca) ratios, Cl/(Cl + SO4) ratios and decreases in 87Sr/86Sr ratios; each mixing trend is consistent with saline groundwater discharges sourced from Cretaceous or Devonian aquifers. These regional subsurface‐to‐surface connections signify that injected wastewater or steam may potentially resurface in the future, emphasizing the critical importance of mapping groundwater flow paths to understand present‐day streamflow quality and to predict the potential for injected fluids to resurface.

Global Isotope Hydrogeology―Review

“…Multiple geochemical tracers are measured and applied to assess groundwater inputs along rivers, including radiocarbon (Bourke et al, ), radon‐222 (e.g., Cook et al, , ; Cook, ; Cartwright et al, ; Campodonica et al, 2015; Cartwright & Gilfedder, ; Cartwright & Hofmann, ; Xie et al, ; Xu et al, ; Avery et al, ), helium‐4 (Gardner et al, ), and chloride or other major ion concentrations, strontium isotopes (e.g., Négrel et al, ; Shand et al, ). Where longitudinal river isotope surveys have been completed, groundwater discharges are frequently found to be densely distributed (e.g., Atkinson et al, ; Cook, ; Ellis & Jasechko, ). The application of synoptic hydrograph separations could better integrate hydrologic connectivity and hydrograph separation research but will require developing river δ 18 O time series at numerous locations along a river (e.g., Racoviteanu et al, ).…”

“…Fossil groundwater recharged during the late‐Pleistocene has been identified in over 100 aquifer systems around the globe (e.g., Münnich & Vogel, ; Edmunds & Wright, ; Fontes, ; Edmunds et al, , ; Darling, ; Haldorsen et al, ; Figure ; Table ). Measurements of fossil groundwater δ 18 O values can provide information about Pleistocene climate conditions (Andrews et al, ; Bertrand et al, ; Haggaz & Kheirallah, ; Joussaume & Jouzel, ) or the fate of paleo‐meltwaters derived from large Pleistocene ice sheets (e.g., the Laurentide ice sheet—Desaulniers et al, ; Siegel & Mandle, ; Bottomley et al, ; Siegel, ; Remenda et al, ; Grasby & Betcher, , ; Clark et al, ; Grasby & Chen, ; Ferguson et al, ; Person et al, ; Jasechko et al, ; McIntosh et al, ; Stotler et al, ; Ferguson & Jasechko, ; Vetter et al, ; Ellis & Jasechko, ; Birks et al, —and the Fennoscandian ice sheet—Boulton et al, ; Vaikmäe, Vallner, et al, ; Vaikmäe, Edmunds, et al, ; Raidla et al, ; Pärn et al, , ; Gerber et al, ). Global climate warmed ~4 °C over the past ~20,000 years (Annan & Hargreaves, ).…”