Abstract
Abstract. Radon-222, a naturally-occurring radioisotope with a half-life of 3.8 days, was used to estimate groundwater discharge to small lakes in wetland-dominated basins in the vicinity of Fort McMurray, Canada. This region is under significant water development pressure including both oil sands mining and in situ extraction. Field investigations were carried out in March and July 2008 to measure radon-222 distributions in the water column of two lakes as a tracer of groundwater discharge. Radon concentrations in these lakes ranged from 0.5 to 72 Bq/m3, while radon concentrations in groundwaters ranged between 2000 and 8000 Bq/m3. A radon mass balance, used in comparison with stable isotope mass balance, suggested that the two lakes under investigation had quite different proportions of annual groundwater inflow (from 0.5% to about 14% of the total annual water inflow). Lower discharge rates were attributed to a larger drainage area/lake area ratio which promotes greater surface connectivity. Interannual variability in groundwater proportions is expected despite an implied seasonal constancy in groundwater discharge rates. Our results demonstrate that a combination of stable isotope and radon mass balance approaches provides information on flowpath partitioning that is useful for evaluating surface-groundwater connectivity and acid sensitivity of individual water bodies of interest in the Alberta Oil Sands Region.
Highlights
Northeastern Alberta is the centre of oil sand mining in Canada
Our results demonstrate that a combination of stable isotope and radon mass balance approaches provides information on flowpath partitioning that is useful for evaluating surface-groundwater connectivity and acid sensitivity of individual water bodies of interest in the Alberta Oil Sands Region
The quantification of groundwater discharging into lakes is essential for evaluating the vulnerability of surface waters in relation to changes in local groundwater flow patterns
Summary
Northeastern Alberta is the centre of oil sand mining in Canada. The intense mining activities in the vicinity of the City of Fort McMurray were established some decades ago. The processes of oil extraction, upgrading and refinement require significant inputs of water, some of which is withdrawn from local aquifers.For in situ mining purposes, groundwater is pumped from the available aquifer system to the surface where it is heated up and re-injected as steam into the oil bearing sands. The resultant decrease in the viscosity of the bitumen allows its pumping to the surface. This practice may trigger considerable changes in the local groundwater flow patterns. One concern related to this process is the potential ecological effect on hydraulically connected surface water bodies
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