Probabilistic modelling and uncertainty analysis of flux and water balance changes in a regional aquifer system due to coal seam gas development J. Sreekanth a, ⁎, Tao Cui a , Trevor Pickett a , David Rassam a , Mat Gilfedder a , Damian Barrett b a CSIRO, Dutton Park 4102, Australia b CSIRO, Black Mountain, Canberra 2601, Australia HIGHLIGHTS • Probabilistic modelling of impact of on- shore gas (coal seam gas) development on water resources • Predictive uncertainty analysis of im- pacts to groundwater flux and water balance • Numerical modelling of groundwater interactions in complex sedimentary basins • Predictive modelling of impacts ac- counting for prediction uncertainties GRAPHICAL ABSTRACT abstract article info Article history: Received 26 February 2018 Received in revised form 7 April 2018 Accepted 8 April 2018 Available online xxxx Editor: D. Barcelo Large scale development of coal seam gas (CSG) is occurring in many sedimentary basins around the world in- cluding Australia, where commercial production of CSG has started in the Surat and Bowen basins. CSG develop- ment often involves extraction of large volumes of water that results in depressurising aquifers that overlie and/ or underlie the coal seams thus perturbing their flow regimes. This can potentially impact regional aquifer sys- tems that are used for many purposes such as irrigation, and stock and domestic water. In this study, we adopt a probabilistic approach to quantify the depressurisation of the Gunnedah coal seams and how this impacts fluxes to, and from the overlying Great Artesian Basin (GAB) Pilliga Sandstone aquifer. The proposed method is suitable when effects of a new resource development activity on the regional groundwater balance needs to be assessed and account for large scale uncertainties in the groundwater flow system and proposed activity. The results indicated that the extraction of water and gas from the coal seam could potentially induce additional fluxes from the Pilliga Sandstone to the deeper formations due to lowering pressure heads in the coal seams. The median value of the rise in the maximum flux from the Pilliga Sandstone to the deeper formations is estimated to be 85 ML/year, which is considered insignificant as it forms only about 0.29% of the Long Term Annual Average Extraction Limit of 30 GL/year from the groundwater management area. The probabilistic simulation of the water balance components indicates only small changes being induced by CSG de- velopment that influence interactions of the Pilliga Sandstone with the overlying and underlying formations and with the surface water courses. The current analyses that quantified the potential maximum impacts of resource develop- ments and how they influences the regional water balance, would greatly underpin future management decisions. © 2018 Elsevier B.V. All rights reserved. Keywords: Groundwater Coal seam gas Uncertainty Modelling Water balance Groundwater flux Science of the Total Environment 634 (2018) 1246–1258 ⁎ Corresponding author. E-mail address: Sreekanth.Janardhanan@csiro.au. (J. Sreekanth). https://doi.org/10.1016/j.scitotenv.2018.04.123 0048-9697/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv