1.1.4 Hydrogeology and groundwater quality


This summary is based on information sourced from environmental impact assessments (EIAs) undertaken by coal mining and coal seam gas (CSG) companies operating in the Gloucester subregion, and on other related documents, such as critiques or peer reviews.

The Gloucester subregion is defined by the underlying Gloucester Basin, a closed hydrogeological system, containing two main aquifers: an alluvial aquifer and an aquifer hosted by a bedrock weathered profile occurring within 150 metres below ground level (mbgl). Hydraulic conductivity reduces exponentially with depth – anything from one to tens of metres per day in an alluvial aquifer and from 10-2 m/day to 10-6 m/day in weathered rock aquifers. There are a series of fault systems, known or inferred, some of which are associated with higher permeability zones in the shallow weathered bedrock profile. However, these fault systems’ connectivity to deeper coal seams and their effects on overall hydrogeological conditions are not well known.

A topographical divide across the middle of the Gloucester Basin influences groundwater and surface water flow. From this divide, regional groundwater flow is predominantly towards the south and the north. Groundwater quality data indicate in-situ mineralisation, with groundwater salinity levels increasing with depth from nearly fresh to brackish. There are also elevated concentrations of strontium, iron, bromine and methane in both aquifers.

Groundwater recharge in alluvial aquifers is associated with river flow and rainfall events, while in other aquifer systems recharge is mainly from rainfall. The recharge estimation varies from zero to 28% of rainfall. Localised discharge occurs to the rivers or as baseflow (3 to 12% of rainfall) and diffuse discharge occurs through vegetation use of shallow groundwater (0.5% of rainfall). In addition, groundwater outflow from the Gloucester Basin occurs along the northern and southern boundaries but was estimated as only a small portion of the groundwater balance (0.06% rainfall). Three groundwater numerical models are available for the Gloucester Basin.

Current groundwater use (up to approximately 0.52 GL/year) comprises commercial or industrial, irrigation, mining, stock, domestic and farming activities.

Last updated:
5 January 2018