Baselining Lower Namoi Groundwater and Evaluating Pilliga CSG Developments

Abstract

This report summarises the primary research outcomes and publications produced as part of CRDC project UNSW1601 Baselining Lower Namoi Groundwater and Evaluating Pilliga CSG Developments. There is considerable public apprehension about the expansion of coal seamgas (CSG) production in the Pilliga. To produce the gas from the Permian coal measures, large quantities of co-produced water will be extracted. This water is commonly of poor quality and once it is brought to the surface there are concerns about its treatment, disposal and subsequent use. There are also concerns about the depressurisation impacts on groundwater resources in the Great Artesian Basin and Lower Namoi Alluvium. This projectassessed potential impacts of CSG production in conjunction with ongoing groundwater withdrawals for irrigated agriculture on sustainable access to groundwater for the cotton industry, as well as stock and domestic users.Measurements of the methane content of groundwater undertaken in the USA have demonstrated that methane levels can be an early indicator of connectivity between coal seam gas developments and aquifers used as water supplies (Osborn et al. 2011). To date there are no extensive baseline measurements of methane concentration in the groundwater or the air in the Namoi Catchment that have been placed in the public domain. This projectestablished baseline methane concentrations in the Lower Namoi Alluvial Aquifer and ground-level atmosphere.Since the establishment of the water sharing plans there have been limited studies reviewing how groundwater levels have responded and whether the groundwater quality is being maintained or improved. To assess changes in water quality the hydrogeochemical data collected as part of this study were compared to historical data sets. Graphs of groundwater levels for all groundwater monitoring locations in the Namoi were produced, along with maps highlighting how the groundwater levels have changed for two periods 1985-2015 and 2006-2015.Throughout Australia there are thousands of abandoned legacy wells. These wells may act as pathways of hydraulic connectivity to enable the transfer of water and gas between the coal measures and overlying aquifers. In 2014 and 2016 as part of CRDC project UNSW1401 mobile surveys were undertaken to measure continuously the methane mole fraction in the ground-level atmosphere of the Condamine catchment. Those campaigns mapped the locations of two legacy wells that were leaking methane at concentrations above ignition potential. Those results demonstrated that the issue of legacy wells requires extensive further study, and that in any region where there is potential for legacy wells to exist surveys should be undertaken. To assess if there are any legacy wells of concern in the Lower Namoi three field campaigns were undertaken to measure the methane mole fraction (concentration) in the ground-level atmosphere. These surveys also created a baseline data set to enable future assessments of changing land use and industrial activities