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TitleMethane variations in groundwater over time
AuthorRivard, C; Bordeleau, G; Lavoie, D; Lefebvre, R; Malet, X
SourceHydrogeology Journal 2017.
Year2017
Alt SeriesNatural Resources Canada, Contribution Series 20170257
PublisherSpringer
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceQuebec
NTS21L/12
AreaSaint-Édouard
Lat/Long WENS -72.0000 -71.5000 47.2500 46.4167
Subjectsgroundwater; methane; hydrocarbon gases; groundwater pollution; groundwater surveys; observation wells; wells; well samples; isotopes; dissolved inorganic carbon (DIC); groundwater monitoring
Illustrationslocation maps; schematic cross-sections; tables; graphs
ProgramShale Gas - groundwater, Environmental Geoscience
AbstractDissolved methane concentrations in shallow groundwater are known to vary both spatially and temporally. The extent of these variations is poorly documented although this knowledge is critical for distinguishing natural fluctuations from anthropogenic impacts stemming from oil and gas activities. This issue was addressed as part of a groundwater research project aiming to assess the risk of shale gas development for groundwater quality over a 500-km 2 area in the St . Lawrence Lowland s (Quebec, Canada). A specific study was carried out to define the natural variability of methane concentrations and carbon and hydrogen isotope ratios in groundwater, as dissolved methane is naturally ubiquitous in aquifers of this area. Monitoring was carried out over a period of up to 2.5 years in seven monitoring wells. Results showed that for a given well, usin g the same sampling depth and technique, methane concentrations can vary over time from 2.5 to 6 times relative to the lowest recorded value. Methane isotopic composition, which is a useful tool to distinguish gas
origin, was found to be stable for most wells, but varied significantly over time in the two wells where methane concentrations are the lowest. The use of concentration ratios, as well as isotopic composition of methane and dissolved inorganic carbon (DIC), helped unravel the processes responsible for these variations. This study indicates that both methane concentrations and isotopic composition, as well as DIC isotopes, should be regularly monitored over at least 1 year to establish their potential natural variations prior to hydrocarbon development.
Summary(Plain Language Summary, not published)
Dissolved methane concentrations in shallow groundwater are known to vary both spatially and temporally. However, the extent of these variations is poorly documented and this knowledge is critical for distinguishing natural fluctuations from anthropogenic impacts stemming from deep industrial activities. A groundwater study was carried out over a 500 km2 area in the St-Édouard region, located in the St. Lawrence Lowlands. The St. Lawrence Lowlands were the target of shale gas exploration between 2006 and 2010, before a moratorium was imposed. Results showed that methane concentrations can vary over time from 2.5 to 6 times the smallest recorded value. Methane isotopes, which are a useful tool to distinguish the gas origin, were found to be stable for most wells, but they varied significantly over time in the two wells where methane concentrations are the lowest. This indicates that both methane concentrations and isotopes should be regularly monitored over at least one year to get a grasp on the potential natural variations prior to any hydrocarbon activity.
GEOSCAN ID306169