Impacts of coal mining and coal seam gas extraction on groundwater and surface water

Abstract This paper presents an assessment of the hydrological impacts of proposed coal mines and coal seam gas (CSG) developments in the Gloucester, Hunter, Namoi and Galilee subregions of eastern Australia. Surface water and groundwater modelling was carried out to assess the cumulative regional-scale hydrological impacts of multiple coal and coal seam gas developments. The hydrological metrics assessed were groundwater drawdown and changes in low-flow characteristics as measured by the number of low-flow or zero flow days per year. Uncertainty in the modelling was also considered, and the results are presented as the median and plausible range (5th to 95th percentile) from many simulations which attempt to capture a wide range of uncertainty. The results indicate that under the best-case (5th percentile) scenario, the impact of additional/proposed coal resource developments on groundwater drawdown and surface water characteristics can be quite small. However, under the worse-case (95th percentile), groundwater drawdown is very likely for up to 5 km from the coal resource developments, but unlikely beyond 20 km. Altered surface water characteristics can extend for many kilometres downstream, particularly in unregulated systems. The cumulative hydrological impact is enhanced where there are multiple developments in close proximity. The results are being used to inform policy and the approval process for coal resource developments.