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TitleThe effect of long-term regional pumping on hydrochemistry and dissolved gas content in an undeveloped shale-gas-bearing aquifer in southwestern Ontario, Canada
AuthorHamilton, S M; Grasby, S EORCID logo; McIntosh, J C; Osborn, S G
SourceHydrogeology Journal vol. 23, issue 4, 2015 p. 719-739, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20140121
PublisherSpringer Nature
Mediapaper; on-line; digital
File formatpdf
NTS30M; 31D; 40; 41A; 41G/03
AreaLondon; Kitchener; Chatham
Lat/Long WENS -83.0000 -78.5000 45.5000 41.7500
Subjectshydrogeology; groundwater; groundwater geochemistry; groundwater resources; aquifers; shales; gas; hydrochemistry; methane
Illustrationslocation maps; tables; plots; histograms
ProgramGeoscience for New Energy Supply (GNES), Shale-hosted petroleum ressource assessment
Released2015 02 03
AbstractBaseline groundwater geochemical mapping of inorganic and isotopic parameters across 44,000 km2 of southwestern Ontario (Canada) has delineated a discreet zone of natural gas in the bedrock aquifer coincident with an 8,000-km2 exposure of Middle Devonian shale. This study describes the ambient geochemical conditions in these shales in the context of other strata, including Ordovician shales, and discusses shale-related natural and anthropogenic processes contributing to hydrogeochemical conditions in the aquifer. The three Devonian shales—the Kettle Point Formation (Antrim equivalent), Hamilton Group and Marcellus Formation—have higher DOC, DIC, HCO3, CO2(aq), pH and iodide, and much higher CH4(aq). The two Ordovician shales—the Queenston and Georgian-Bay/Blue Mountain Formations—are higher in Ca, Mg, SO4 and H2S. In the Devonian shale region, isotopic zones of Pleistocene-aged groundwater have halved in size since first identified in the 1980s; potentiometric data implicate regional groundwater extraction in the shrinkage. Isotopically younger waters invading the aquifer show rapid increases in CH4(aq), pH and iodide with depth and rapid decrease in oxidized carbon species including CO2, HCO3 and DIC, suggesting contemporary methanogenesis. Pumping in the Devonian shale contact aquifer may stimulate methanogenesis by lowering TDS, removing products and replacing reactants, including bicarbonate, derived from overlying glacial sedimentary aquifers.
Summary(Plain Language Summary, not published)
Growing interest in sustainable development of shale-gas resources has motivated research to examine a region of known shale-gas potential in pre-development conditions in southern Ontario. While no shale-gas has been developed in this region it has been the focus of extensive groundwater developments for rural residential dwellings. This has altered the groundwater chemistry to conditions that are more favorable to microbial communities that produce methane in the sub-surface. This localised biologic methane formation thus can increase the amount of methane in the water wells. These results demonstrate that simple development of groundwater systems can induce localised methane generation.

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