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Measuring Carbon-based Contaminant Mineralization Using Combined CO2 Flux and Radiocarbon Analyses
Published on: October 21, 2016
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A dynamic baseline for dissolved methane in English groundwater
M P Wilson1, F Worrall1, R J Davies2
1Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, UK.
The Science of the Total Environment
|December 11, 2019
Summary
Establishing baseline dissolved methane (CH4) in English groundwater is crucial for monitoring shale gas impacts. A Bayesian approach refined environmental data, revealing generally low methane levels but identifying areas exceeding risk thresholds.
Area of Science:
- Environmental Science
- Geochemistry
- Hydrogeology
Background:
- Elevated dissolved methane (CH4) in groundwater is a key environmental concern linked to hydraulic fracturing for shale gas.
- Establishing reliable dissolved CH4 baselines is essential for detecting and understanding potential environmental impacts from energy extraction activities.
- Groundwater CH4 baselines must dynamically reflect environmental changes and predict the probability of concentration shifts.
Purpose of the Study:
- To determine baseline dissolved methane (CH4) concentrations in English groundwater.
- To assess the effectiveness of a Bayesian approach in refining CH4 datasets for environmental monitoring.
- To investigate the relationship between groundwater redox conditions and elevated CH4 levels.
Main Methods:
- Utilized a Bayesian approach to analyze four dissolved CH4 datasets from English groundwater (two national, two local).
- Integrated a sensitive national dataset (British Geological Survey) as a strong prior for a less sensitive, larger national dataset (Environment Agency).
- Analyzed groundwater redox parameters, including Fe concentration, in relation to CH4 levels.
Main Results:
- The Bayesian approach improved the precision of the Environment Agency dataset by 75% using a strong prior.
- The expected mean dissolved CH4 concentration in English groundwater is 0.24 mg/l (95% credible interval: 0.11–0.45 mg/l).
- Estimated annual CH4 degassing from English groundwater ranges from 0.7 to 3.1 kt/year (expected value 1.65 kt/year).
- Identified locations with CH4 concentrations ≥10.0 mg/l, exceeding the risk action level, and suggested redox parameters for identifying similar sites.
Conclusions:
- The Bayesian method significantly enhances the precision of large-scale groundwater CH4 datasets.
- English groundwater CH4 degassing contributes significantly to atmospheric methane, with a notable greenhouse gas warming potential.
- Redox conditions, particularly Fe concentration, may serve as indicators for identifying groundwater sites with high dissolved CH4 concentrations.
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