Irrigation bore water in the Condamine Catchment: baselining groundwater quality and assessing pathways of hydraulic connectivity

Abstract

The expansion of coal seam gas production adjacent to the irrigation farming districts in the Condamine Catchment has raised concerns about the impact of gas production on groundwater in adjoining aquifer systems. To assess the risk, and to be able to detect any future changes in groundwater properties, existing groundwater chemistry data sets need to be updated and expanded. Historically, the testing of groundwater chemistry in the Condamine Catchment has focused on the Queensland Government groundwater-monitoring network, but it is unlikely that these samples come from the same sand and gravel bodies from which the irrigation bores extract groundwater. We report the result of 20 groundwater samples collected from bores that supply irrigation water for cotton and other crops. These samples were collected in January 2014 at the end of the pumping season, when the aquifer system is at peak stress for the year. We compare the major ion chemistry recorded in the irrigation bores to that measured at selected sites from the QLD government groundwater-monitoring network and with historical results reported in the literature. A hydrochemical facies analysis of these data provides one assessment of the likelihood of hydraulic connectivity between the Walloon Coal Measures, other bordering Great Artesian Basin formations and the valley filling sediments of the Condamine Alluvium. The results highlight variation in groundwater chemistry within the Condamine Alluvium, particularly in the Cecil Plains and Dalby regions, where there are signs of water mixing. As a result, further research into the area to explain the baseline data sets would provide a better understanding of hydraulic connectivity and the potential effects of CSG on the groundwater.