An 8-year record of gas geochemistry and isotopic composition of methane during baseline sampling at a groundwater observation well in Alberta (Canada)

Humez, Pauline; Mayer, Bernhard; Nightingale, Michael; Ing, Jennifer; Becker, Veith; Jones, D. D.; Lam, Vien

doi:10.1007/s10040-015-1319-1

Cited by 26 publications

(26 citation statements)

References 20 publications

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“…Within the ARB, Environment Canada maintained six streamflow gauging stations along the Athabasca River (HYDAT, ), which are located at Jasper, Hinton, Windfall, Athabasca, Fort McMurray, and Embarras Airport, and the Government of Alberta Groundwater Observation Well Network (GOWN) maintained groundwater monitoring wells operated by the Government of Alberta (Figure ). Details describing the GOWN and its well installation can be found in Government of Alberta () and Humez et al (), respectively. Using the locations of the stream flow gauging stations, the basin is divided into six sub‐basins (i.e., Jasper [JA], Hinton [HT], Windfall [WF], Athabasca [AT], Fort McMurray [FM], and Embarras Airport [EA] sub‐basins).…”

Section: Methodsmentioning

confidence: 99%

Understanding the water balance paradox in the Athabasca River Basin, Canada

Hwang

Park

Sudicky

et al. 2018

Hydrological Processes

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This study demonstrates the importance of the including and appropriately parameterizing peatlands and forestlands for basin‐scale integrated surface–subsurface models in the northern boreal forest, with particular emphasis on the Athabasca River Basin (ARB). With a long‐term water balance approach to the ARB, we investigate reasons why downstream mean annual stream flow rates are consistently higher than upstream, despite the subhumid water deficit conditions in the downstream regimes. A high‐resolution 3D variably saturated subsurface and surface water flow and evapotranspiration model of the ARB is constructed based on the bedrock and surficial geology and the spatial distribution of peatlands and their corresponding eco‐regions. Historical climate data were used to drive the model for calibration against 40‐year long‐term average surface flow and groundwater observations during the historic instrumental period. The simulation results demonstrate that at the basin‐scale, peatlands and forestlands can have a strong influence on the surface–subsurface hydrologic systems. In particular, peatlands in the midstream and downstream regimes of the ARB increase the water availability to the surface–subsurface water systems by reducing water loss through evapotranspiration. Based on the comparison of forestland evapotranspiration between observation and simulation, the overall spatial average evapotranspiration in downstream forestlands is larger than that in peatlands and thus the water contribution to the stream flow in downstream areas is relatively minor. Therefore, appropriate representation of peatlands and forestlands within the basin‐scale hydrologic model is critical to reproduce the water balance of the ARB.

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Section: Methodsmentioning

confidence: 99%

Understanding the water balance paradox in the Athabasca River Basin, Canada

Hwang

Park

Sudicky

et al. 2018

Hydrological Processes

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“…A detailed description of the sampling equipment and procedures for free and dissolved gas samples is given in Humez et al (2016b). The composition of free and dissolved gas samples was determined in the laboratory by gas chromatography yielding concentrations for oxygen, carbon dioxide, methane, and higher alkane chain compounds (such as ethane) with measurements conducted by AITF with uncertainties of ±5 % of the analytes.…”

Section: Gas Compositionmentioning

confidence: 99%

Redox controls on methane formation, migration and fate in shallow aquifers

Humez¹,

Mayer²,

Nightingale³

et al. 2016

Hydrol. Earth Syst. Sci.

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Abstract. Development of unconventional energy resources such as shale gas and coalbed methane has generated some public concern with regard to the protection of groundwater and surface water resources from leakage of stray gas from the deep subsurface. In terms of environmental impact to and risk assessment of shallow groundwater resources, the ultimate challenge is to distinguish (a) natural in situ production of biogenic methane, (b) biogenic or thermogenic methane migration into shallow aquifers due to natural causes, and (c) thermogenic methane migration from deep sources due to human activities associated with the exploitation of conventional or unconventional oil and gas resources. This study combines aqueous and gas (dissolved and free) geochemical and isotope data from 372 groundwater samples obtained from 186 monitoring wells of the provincial Groundwater Observation Well Network (GOWN) in Alberta (Canada), a province with a long record of conventional and unconventional hydrocarbon exploration. We investigated whether methane occurring in shallow groundwater formed in situ, or whether it migrated into the shallow aquifers from elsewhere in the stratigraphic column. It was found that methane is ubiquitous in groundwater in Alberta and is predominantly of biogenic origin. The highest concentrations of biogenic methane ( > 0.01 mM or > 0.2 mg L −1 ), characterized by δ 13 C CH 4 values < −55 ‰, occurred in anoxic Na-Cl, Na-HCO 3 , and Na-HCO 3 -Cl type groundwaters with negligible concentrations of nitrate and sulfate suggesting that methane was formed in situ under methanogenic conditions for 39.1 % of the samples. In only a few cases (3.7 %) was methane of biogenic origin found in more oxidizing shallow aquifer portions suggesting limited upward migration from deeper methanogenic aquifers. Of the samples, 14.1 % contained methane with δ 13 C CH 4 values > −54 ‰, potentially suggesting a thermogenic origin, but aqueous and isotope geochemistry data revealed that the elevated δ 13 C CH 4 values were caused by microbial oxidation of biogenic methane or postsampling degradation of low CH 4 content samples rather than migration of deep thermogenic gas. A significant number of samples (39.2 %) contained methane with predominantly biogenic C isotope ratios (δ 13 C CH 4 < −55 ‰) accompanied by elevated concentrations of ethane and sometimes trace concentrations of propane. These gases, observed in 28.1 % of the samples, bearing both biogenic (δ 13 C) and thermogenic (presence of C 3 ) characteristics, are most likely derived from shallow coal seams that are prevalent in the Cretaceous Horseshoe Canyon and neighboring formations in which some of the groundwater wells are completed. The remaining 3.7 % of samples were not assigned because of conflicting parameters in the data sets or between replicates samples. Hence, despite quite variable gas concentrations and a wide range of δ 13 C CH 4 values in baseline groundwater samples, we found no conclusive evidence for deep thermogenic gas migration into shallow aqu...

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“…More specifically, Jackson states that a single dissolved methane concentration in groundwater with an isotopic signature is not sufficient to interpret its implications. Some studies have shown that methane concentrations in groundwater can be quite variable, which can be due to a mode of methane migration by ‘slugs.’ Variability in baseline groundwater methane over 8 years was assessed using free and dissolved gas sampling for a groundwater monitoring well in Alberta (Canada) . This study showed wide variations in methane concentrations but quite stable isotopic signatures, and it emphasizes that adequate and invariable procedures are needed to generate representative methane analyses that can be used to assess the potential impact of O&G development on groundwater quality.…”

Section: Recognition Of Groundwater Contaminationmentioning

confidence: 99%

Mechanisms leading to potential impacts of shale gas development on groundwater quality

Lefebvre

2016

WIREs Water

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The development of shale gas resources was made possible by the combination of horizontal drilling and high‐volume hydraulic fracturing (fracking). Environmental concerns have been raised relative to shale gas production, especially potential impacts on groundwater. Fluids related to unconventional oil and gas (O&G) operations contain chemical compounds that can impact groundwater quality. Such impacts can occur due to (1) the infiltration of surface contaminant releases, (2) failures of the integrity of O&G wells, and (3) upward fluid migration from a shale/tight reservoir along preferential paths that can be natural (faults or fracture zone) or man‐made (O&G wells). Surface releases represent the most probable mechanism leading to groundwater contamination. Improvements in O&G drilling operations under stringent regulations can minimize this risk. Experts identify O&G well integrity as the most challenging issue that may lead to groundwater contamination. Failure of casing and cement can lead to upward fluid flow within or outside O&G wells, especially of methane. Integrity failures leading to fluid migration to shallow fresh water aquifers or to the surface are well understood and can be detected and repaired, but this can be complex and costly. A few regulators now impose groundwater monitoring to detect impacts from integrity failures. Occurrences of communication with existing O&G wells from fracking operations have also led some regulators to impose rules aiming to avoid such potential fluid migration paths. There is an ongoing scientific debate regarding the potential for fluids to migrate upward from exploited shale gas units to aquifers through natural preferential paths. WIREs Water 2017, 4:e1188. doi: 10.1002/wat2.1188 This article is categorized under: Engineering Water > Sustainable Engineering of Water Science of Water > Water Quality

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An 8-year record of gas geochemistry and isotopic composition of methane during baseline sampling at a groundwater observation well in Alberta (Canada)

Cited by 26 publications

References 20 publications

Understanding the water balance paradox in the Athabasca River Basin, Canada

Understanding the water balance paradox in the Athabasca River Basin, Canada

Redox controls on methane formation, migration and fate in shallow aquifers

Mechanisms leading to potential impacts of shale gas development on groundwater quality

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