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TitleCan groundwater sampling techniques used in monitoring wells influence methane concentrations and isotopes?
AuthorRivard, CORCID logo; Bordeleau, G; Lavoie, DORCID logo; Lefebvre, R; Malet, X
SourceEnvironmental Monitoring and Assessment vol. 190, issue 4, 191, 2018 p. 1-17,
Alt SeriesNatural Resources Canada, Contribution Series 20170288
PublisherSpringer Nature
Mediapaper; on-line; digital
File formatpdf; html
Lat/Long WENS -71.9500 -71.7000 46.6833 46.5000
Subjectshydrogeology; environmental geology; fossil fuels; geochemistry; sampling techniques; groundwater geochemistry; wells; observation wells; gas wells; water wells; petroleum industry; hydrocarbons; gas; methane; stable isotope studies; carbon; hydrogen; concentration; well samples; bedrock geology; lithology; sedimentary rocks; structural features; faults, normal; faults, thrust; folds; anticlines; synclines; Leclercville Anticline; Chambly-Fortierville Syncline; Lorraine Group; Pontgravé Formation; Nicolet Formation; Sainte-Rosalie Group; Lotbinière Formation; Les Fonds Formation; Utica Shale; Bourret Formation; Methodology; Equipment; monitoring; Phanerozoic; Paleozoic; Ordovician
Illustrationslocation maps; geoscientific sketch maps; tables; plots; bar graphs
ProgramEnvironmental Geoscience Shale Gas - groundwater
Released2018 03 06
AbstractMethane concentrations and isotopic composition in groundwater are the focus of a growing number of studies. However, concerns are often expressed regarding the integrity of samples, as methane is very volatile and may partially exsolve during sample lifting in the well and transfer to sampling containers. While issues concerning bottle-filling techniques have already been documented, this paper documents a comparison of methane concentration and isotopic composition obtained with three devices commonly used to retrieve water samples from dedicated observation wells. This work lies within the framework of a larger project carried out in the Saint-Édouard area (southern Québec, Canada), whose objective was to assess the risk to shallow groundwater quality related to potential shale gas exploitation. The selected sampling devices, which were tested on ten wells during three sampling campaigns, consist of an impeller pump, a bladder pump, and disposable sampling bags (HydraSleeve). The sampling bags were used both before and after pumping, to verify the appropriateness of a no-purge approach, compared to the low-flow approach involving pumping until stabilization of field physicochemical parameters. Results show that methane concentrations obtained with the selected sampling techniques are usually similar and that there is no systematic bias related to a specific technique. Nonetheless, concentrations can sometimes vary quite significantly (up to 3.5 times) for a given well and sampling event. Methane isotopic composition obtained with all sampling techniques is very similar, except in some cases where sampling bags were used before pumping (no-purge approach), in wells where multiple groundwater sources enter the borehole.
Summary(Plain Language Summary, not published)
Sampling groundwater highly charged with dissolved gases is challenging, since water degasses while being pumped and brought to the surface. A specific study was carried out in the St-Édouard area (southern Québec) to investigate the impact of different sampling techniques used in observation wells for methane concentrations and isotopes. Three common sampling devices (two types of submersible pumps and disposable bags) were tested. Results showed that methane concentrations were usually similar, but can nonetheless vary quite significantly (up to 3.5 times) on an event to event basis. Isotopic values obtained with all sampling techniques were very similar. Because all groundwater sampling techniques share issues related to degassing, three different types of downhole sensors were installed in the study area, but they did not provide reliable results due to the high methane concentrations in groundwater.

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