Distribution of total dissolved solids in McMurray Formation water in the Athabasca oil sands region, Alberta, Canada: Implications for regional hydrogeology and resource development

Abstract

A B S T R A C T Total dissolved solids (TDS) concentrations of 258 LowerCretaceous McMurray Formation water samples in the Athabasca oil sands region (54 to 58°N and 110 to 114°W) were mapped using published data from recent government reports and environmental impact assessments. McMurray Formation waters varied from nonsaline (240 mg/L) to brine (279,000 mg/L) with a regional trend of high salinity water approximately following the partial dissolution front of the Devonian Prairie Evaporite Formation. The simplest hydrogeological explanation for the observed formation water salinity data is that Devonian aquifers are locally connected to the McMurray Formation via conduits in the sub-Cretaceous karst system in the region overlying the partial dissolution front of the Prairie Evaporite Formation. The driving force for upward formation water flow is provided by the Pleistocene glaciation events that reversed the regional Devonian flow system over the past 2 m.y. in the Athabasca region. This study demonstrates that a detailed approach to hydrogeological assessment is required to elucidate TDS concentrations in McMurray Formation waters at an individual lease-area scale. The observed heterogeneity in formation water TDS and the potential for present day upward flow has implications for both mining and in situ oil sands resource development.

Formation waters discharge to rivers near oil sands projects

“…The central result of this research is that groundwater discharges have a major influence on river water chemistry in the AOSR and that these groundwater discharges are concentrated near oil sands leases where rivers incise into Cretaceous‐ and Devonian‐aged formations. Measured increases in river water salinity occur close to the Prairie Evaporite dissolution front that trends NW‐SE across a ~100‐km‐wide zone throughout the study area; dissolution of these evaporites has generated high‐salinity groundwaters (Cowie et al, ; Gue et al, ).…”

“…Because groundwater sourced in Cretaceous and/or Devonian aquifers discharges to rivers and impacts their chemistry, there may exist potential for injected wastewater to impact surface water quality in the future. Cross‐formational flow may be a potential conduit for deep formation waters to reach rivers near steam assisted gravity drainage projects (Cowie et al, ; Hrudey et al, ; Taylor et al, ). The time lags before injected waters that may enter rivers remain poorly characterized in the region; such time lags may be considerably longer than typical management time frames of years, decades, or even centuries. It is important to understand links between geology, saline groundwater, and surface waters in the AOSR, as it may help to establish baseline chemistry for the region.…”

“…Pleistocene‐age glacial meltwaters—groundwaters recharged beneath the Laurentide ice sheet more than 12,000 years ago (Grasby & Chen, ; Gue et al, )—have dissolved Devonian‐aged evaporites, creating an extensive subsurface karst network, resulting in collapse structures and subvertical fracturing (Broughton, , ; Hoffman, ). These fracture networks may provide conduits that enable deep saline groundwaters to reach the surface (Cowie, James, & Mayer, ; Gue et al, ). Groundwater salinity (i.e., total dissolved solids) varies widely, ranging from 240 mg/L to 279,000 mg/L in Cretaceous‐aged aquifers (Cowie et al, ).…”

“…These fracture networks may provide conduits that enable deep saline groundwaters to reach the surface (Cowie, James, & Mayer, ; Gue et al, ). Groundwater salinity (i.e., total dissolved solids) varies widely, ranging from 240 mg/L to 279,000 mg/L in Cretaceous‐aged aquifers (Cowie et al, ). Groundwaters close to the evaporite dissolution front tend to be more saline (Cowie, ; Cowie et al, ; Gue et al, ).…”

“…Groundwater salinity (i.e., total dissolved solids) varies widely, ranging from 240 mg/L to 279,000 mg/L in Cretaceous‐aged aquifers (Cowie et al, ). Groundwaters close to the evaporite dissolution front tend to be more saline (Cowie, ; Cowie et al, ; Gue et al, ). Regional variations in groundwater salinity are likely impacted by spatial variability in evaporite dissolution and in groundwater flow paths.…”