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Regional groundwater conditions in northeast BC : results from a monitoring well network in an area of historical and ongoing unconventional natural gas development

University of British Columbia

Whether oil and gas development pervasively introduces natural gas into shallow groundwater systems remains a controversial issue. While dissolved thermogenic methane attributed to petroleum development activities has been documented at shallow depths in some locations, various studies have also shown that this methane is naturally occurring, even in regions with heavy development. Here, we assess natural gas in near-surface (<110 m) groundwater in the Peace Region of Northeast British Columbia (NEBC), an area of extensive historic and contemporary energy development, by installing a network of 29 purpose-built monitoring wells (MW) across the region, some as close as 70 m to an energy well. Analyses of groundwater samples from the MWs suggest that dissolved methane, microbial in origin, is ubiquitous at low concentration (< 2 mg/L) in the critical zone of the study area. Based on gas composition and isotopic signatures, only one MW showed signs of potential thermogenic gas from a nearby energy well, indicating that discrete unintentional leakage from energy wells can occur in the study area. However, no evidence of pervasive thermogenic natural gas was found. Additionally, within the same study area, groundwater collected from the domestic supply wells in the District of Hudson’s Hope buried valley aquifer show very high methane concentrations (>28 mg/L) with isotopic signatures of a thermogenic coal bed methane (CBM) source. This finding suggests that high levels of naturally-occurring methane may be of concern in the region where highly transmissive aquifers intercept coal-bearing bedrock. Lastly, as a sub-study, the hydrogeology of a paleovalley system within the study area was conceptualized using data from newly installed MWs and available hydrogeological data for buried-valley aquifer systems in NEBC and the Western Canadian Sedimentary Basin (WCSB). Using this conceptual model, a regional-scale, steady-state, groundwater-flow model was constructed to assess recharge magnitude and mechanisms, and residence times to inform aquifer management. Among model results, the calibrated average aerial recharge rate was 16 mm/a, within the range of recharge estimates previously reported for NEBC. Our findings can support management of groundwater resources in similar hydrogeological settings common to NEBC.

Text; Other

2021-03-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/77575

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/