The Australian Government's Geological and Bioregional Assessment (GBA) Program is assessing the potential impacts of shale, tight and deep coal gas development on water and the environment in three regions: the Cooper, Isa and Beetaloo GBA regions.
This presentation will demonstrate how integrating geological structures with hydrochemistry and environmental tracers can greatly support the identification of hydrological connectivity pathways from stressors to environmental assets.
Stressors include the development of prospective unconventional gas plays and groundwater extraction to support development. Environmental assets include groundwater dependent ecosystems (e.g. streams, wetlands, waterholes and springs) and shallow aquifers.
Potential connectivity pathways were identified by assessing multiple independent lines of evidence. Hydraulic pressure data, hydrochemistry from hundreds of bores, surface water and springs, dissolved methane concentrations in groundwater, stable and radioisotopes and noble gases data were interrogated within three-dimensional geological modelling platforms.
The spatial distribution of the data points in relation to geological structures and environmental assets supported the development of alternative conceptualisations of surface water – groundwater connectivity and an indication of aquifer sources to springs.
In addition, six potential connectivity pathways for liquid or gas migration through the route “stressors > aquitards > aquifers > assets”(not always in this order) were proposed to occur via: i. deep seated (reactivated) faults; ii. direct stratigraphic contacts; iii. flow through porous and karstic aquifers, partial aquifers and aquitards; iv. contact between gas plays and overlying aquifers near basin margins; v. catchment constrictions and river diversions; and vi. direct karstic/fractured aquifer discharge into springs.
The conceptual models allowed the identification of data gaps and the design of a data collection program for subsequent stages of the project, including the assessment of potential impacts to water resources and the environment. The proposed approach and lessons learned in this project can be successfully used in other large sedimentary basins.