DISTRIBUTION AND ISOTOPIC CHARACTERIZATION OF METHANE IN A CONFINED AQUIFER IN SOUTHERN ONTARIO, CANADA

Methane is one of the major carbon pools in the groundwater of the confined Alliston Aquifer. Geochemical, geological and hydrological tools were used to evaluate the origin and distribution of this hydrocarbon. The potential sources for methane were migration of thermocatalytic methane from bedrock units and in situ production by bacteria-mediated reactions. The distribution of methane in the aquifer excludes the possibility that methane occurrences were controlled by the nature of the underlying bedrock (limestone vs. shale). C-13 and H-2 data in CH4 from aquifer and bedrock wells indicate that these gases are microbial in origin and they are formed in situ, mainly by CO2 reduction. Chemical and C-14 data in CH4 and DOC support the hypothesis of the existence of carbon sources for in situ microbial production of CH4 in the aquifer.