ABSTRACT

High volumes of groundwater are pumped from aquifers or naturally released through springs or seeps. In the Great Artesian Basin (GAB) various industries, agriculture, feedlots, town water supply, and private landholders extract groundwater. In a component basin, the Surat Basin, coal seam gas (CSG) is also extracted from the Walloon Coal Measures. Gassy water bores can cause pump locks, and other hazards for landholders. High concentrations of dissolved and free gas have been measured in different GAB aquifers, both above and below the CSG reservoir. For example, deep water bores sampled in the Hutton and Precipice sandstone aquifers contained up to 2100 mg/L dissolved methane. CSG production water contained up to 31 mg/L methane. Dissolved methane was sampled via several methods, and emission estimates determined using estimated pumped water volumes and measured methane concentrations. New emission factors were determined for groundwater pumping, and for CSG production water. The existing emission factors for CSG production water (used by the Australia Government) were taken from a USA emission factor originating from a simulation study. We found it to be an order of magnitude higher than emission factors determined from our data. We conclude that: (1) current CSG produced water emission factors may not represent Australian conditions and overestimate emissions; and (2) current standard dissolved methane sampling is not fit for purpose, especially for gassy bores and hot deep groundwaters.