Multi-component mass transfer of background dissolved gases and stray methane gas in shallow groundwater systems
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Authors
Calvert, Madeline
Date
Type
thesis
Language
eng
Keyword
Multi-component mass transfer , Groundwater , Stray gas , Hydrogeology , Gas migration
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Abstract
The goal of this research was to investigate the effects of multi-component mass transfer between methane gas and background dissolved gases (e.g., nitrogen) to improve stray gas detection techniques and advance understanding of methane persistence following a repaired leak. This was achieved by conducting a series of gas injection experiments in a quasi-two-dimensional flow cell (40 × 39.6 × 1.15 cm) simulating an active gas leak and a post-repair scenario and developing simple single cell numerical models of the active (steady-state) leak and the post-repair (kinetic) dissolution. Experiments were conducted at two aqueous fluxes (3.8 m/day and 0.9 m/day) and two heterogeneities (pool- and finger-dominated source architectures). Dissolved oxygen was measured in the effluent water as a representative of background dissolved gases and light transmission techniques were used to quantify gas saturations. A steady-state model was developed to predict the mass transfer rate coefficient for each experiment and the changes in background dissolved gases under a range of conditions. A kinetic model was developed to predict the gas saturations and dissolved gas concentrations during post-repair dissolution, testing the sensitivity of mass transfer rate coefficients and single- and multi-component dissolved gases. Experiments showed that background dissolved gas detectability was highest at slow groundwater fluxes and in pooled source architectures. The steady-state model indicated that the detectability of background dissolved gases was proportional to the initial background dissolved gas concentration in the groundwater, however, the dissolved source gas concentrations remained relatively unchanged with depleted background dissolved gases. Experiments also showed that more time was required for background dissolved gases to return to baseline conditions post repair in pooled source architectures. Kinetic model simulations indicated that a constant mass transfer rate coefficient was sufficient to predict experimental data, as a transient mass transfer rate coefficient did not substantially improve the model fit. The kinetic model also demonstrated that gas persistence was longer in simulations that considered multiple dissolved gases compared to a single-component model. The findings of this study indicate that background dissolved gases may be a useful tool for stray gas detection and that gas persistence is influenced by multiple dissolved gases.
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ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.