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TitleGeochemistry of groundwater in the Saint-Édouard area, Quebec, Canada, and its influence on the distribution of methane in shallow aquifers
AuthorBordeleau, G; Rivard, C; Lavoie, D; Lefebvre, R; Malet, X; Ladeveze, P
SourceApplied Geochemistry vol. 89, 2018 p. 92-108, https://doi.org/10.1016/j.apgeochem.2017.11.012
Year2018
Alt SeriesEarth Sciences Sector, Contribution Series 20160356
PublisherElsevier
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceQuebec
NTS21L/12
AreaSaint-Édouard
Lat/Long WENS -71.5000 -71.0000 46.7500 46.5000
Subjectsenvironmental geology; geochemistry; hydrogeology; groundwater; methane; oil shales; shales; environmental impacts; environmental controls; hydrologic environment; hydrocarbons; groundwater pollution; groundwater surveys; groundwater geochemistry; brine wells; Ultica shale; formation brine
Illustrationslocation maps; graphs; plots; schematic diagrams
ProgramShale Gas - groundwater, Environmental Geoscience
AbstractShale gas and tight oil production has undergone a tremendous increase in the last decade in North America, which was accompanied by animated scientific debate and local public uproar concerning environmental issues, especially the risks of contamination for shallow groundwater resources. In Quebec (eastern Canada), public concerns led to a de facto fracking moratorium in 2010 for the St. Lawrence Lowlands, where the underlying Utica Shale is known to contain significant gas resources. As only a few exploration gas wells have been drilled, this area may still be considered ¿virgin¿ with respect to exploitation. In 2012, a 4-year project was initiated by the Geological Survey of Canada, which aimed at characterizing aquifer vulnerability to deep industrial activities in the St-Édouard region, located close to Quebec City in the St Lawrence Lowlands. As part of this project, a baseline study of hydrocarbons and other geochemical parameters was conducted in shallow aquifers. This paper presents groundwater geochemical characteristics in the region and assesses the geological, hydrogeological and geochemical controls on methane distribution.
Results show that methane is present in 96% of the 48 sampling points over the 500 km2 study area, and that concentrations are highly variable (from 0.006 mg/L to above 80 mg/L), sometimes over short distances and through time. Methane concentrations appear to be related to specific hydrogeochemical conditions, such as those found below the active groundwater flow zone (0-30 m), where relatively old, chemically evolved water is found under semi-confined to confined conditions. Two main fault zones are well documented in the area, and there is clear evidence that some deep formation brines, in addition to marine water originating from the Champlain Sea, are migrating into shallow aquifers in the vicinity of the Jacques-Cartier River fault in the northern part of the study area. This salty groundwater contribution is attributed to the regional groundwater flow coming from the Appalachians and discharging along this normal fault zone close to the St. Lawrence River. The depth from which the brine originates is, however, unknown, There is no indication that deep thermogenic gas from the Utica Shale is currently reaching the surface, through this pathway or elsewhere in this region.
Summary(Plain Language Summary, not published)
In 2012, a 4-year multidisciplinary project was initiated by the Geological Survey of Canada, which aimed at characterizing the vulnerability of groundwater resources to deep industrial shale gas activities in the St-Édouard region, located close to Quebec City in the St Lawrence Lowlands. This paper presents the natural shallow groundwater geochemistry and the distribution of methane in this area. Results show that methane is ubiquitous in the region, and that its presence is mostly related to specific aquifer conditions such as long water residence times and absence of oxygen. While there is evidence that small amounts of deep formation brines migrate into shallow aquifers near the Jacques-Cartier River fault, there is no indication that deep thermogenic gas from the Utica Shale is currently reaching the surface through this fault zone or elsewhere in this region.
GEOSCAN ID299723