Humez, P.Mayer, B.Nightingale, M.Ing, J.Becker, V.Jones, D.Lam, V.2023-02-062023-02-062016-02-01Humez, P., Mayer, B., Nightingale, M., Ing, J., Becker, V., Jones, D., & Lam, V. (2016). An 8-year record of gas geochemistry and isotopic composition of methane during baseline sampling at a groundwater observation well in Alberta (Canada). Hydrogeology Journal, 24(1), 109–122. https://doi.org/10.1007/s10040-015-1319-1http://hdl.handle.net/1880/115820https://dx.doi.org/10.11575/PRISM/40713Variability in baseline groundwater methane concentrations and isotopic compositions was assessed while comparing free and dissolved gas sampling approaches for a groundwater monitoring well in Alberta (Canada) over an 8-year period. Methane concentrations in dissolved gas samples (n = 12) were on average 4,380 ± 2,452 μg/L, yielding a coefficient of variation (CV) >50 %. Methane concentrations in free gas samples (n = 12) were on average 228,756 ± 62,498 ppm by volume, yielding a CV of 27 %. Quantification of combined sampling, sample handling and analytical uncertainties was assessed via triplicate sampling (CV of 19 % and 12 % for free gas and dissolved gas methane concentrations, respectively). Free and dissolved gas samples yielded comparable methane concentration patterns and there was evidence that sampling operations and pumping rates had a marked influence on the obtained methane concentrations in free gas. δ13CCH4 and δ2HCH4 values of methane were essentially constant (−78.6 ± 1.3 and −300 ± 3 ‰, respectively) throughout the observation period, suggesting that methane was derived from the same biogenic source irrespective of methane concentration variations. The isotopic composition of methane constitutes a robust and highly valuable baseline parameter and increasing δ13CCH4 and δ2HCH4 values during repeat sampling may indicate influx of thermogenic methane. Careful sampling and analytical procedures with identical and repeatable approaches are required in baseline-monitoring programs to generate methane concentration and isotope data for groundwater that can be reliably compared to repeat measurements once potential impact from oil and gas development, for example, may occur.engThis version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: http://dx.doi.org/10.1007/s10040-015-1319-1 Unless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.journal article10.1007/s10040-015-1319-1