The Office of Groundwater Impact Assessment (OGIA) is responsible for preparing an Underground Water Impact Report (UWIR) for ‘cumulative management areas’ (CMA) i.e. areas where the impacts of water extraction for multiple resource development activities overlap. In 2011, the Surat CMA was declared and the first UWIR was published in 2012. As part of this UWIR a regional groundwater flow model was developed to predict the cumulative impacts of groundwater extraction by Coal Seam Gas (CSG) activities within the Surat CMA. Since this time OGIA has undertaken several studies to address a number of unique modelling challenges that apply to assessing the impact of coal seam gas extraction on regional groundwater systems. These studies culminated in a revised groundwater model that was used to re-predict impacts for the purposes of the 2016 Surat CMA UWIR. This presentation will highlight some of the adopted methodologies with potential for wider application to other CSG development areas, including: 1) the development of a revised version of the MODFLOW-USG groundwater flow modelling code to approximate dual-phase flow in coal seams; 2) simulation of CSG extraction using a “descending drain” methodology that recognizes the gas filled nature of CSG wells; and 3) initial parameterization of the regional model using stochastic lithology permeability models and “numerical permeameters”. The presentation will conclude with the model predictions that are most relevant to OGIA’s stakeholders and identify areas for further research.