Hydraulic Connectivity Between Mines and Adjacent River and Groundwater Systems in the Hunter River Valley

This project aimed to improve understanding and quantification of the hydraulic connectivity between open cut mines and adjacent river and groundwater systems at the study site in the Hunter River Valley. The investigation focussed on fault and fracture zones that underpin such connectivity by providing preferential flow pathways. An integrated approach combining field measurements and numerical modelling was applied to achieve the objectives of the project.

In the field, non-invasive technologies were used to identify and examine fault and fracture zones. In particular, a new method based on the coupling of soil gas mapping and gamma ray survey was developed and tested for localising decametre-scale permeable structures. Using this method over two field campaigns, we confirmed the presence of two fault zones that were inferred from a previous geological model. However, our data revealed an eastern shift of their locations by 25 m. Moreover, the method led to the discovery of an additional fault zone at the site, which was verified by a drilling program carried out afterwards. Combined with borehole flow measurements and gas transport modelling, this new method also enabled the determination of the permeability of the fault and fracture zones as well as the associated gas release rates.

The key outcomes produced by the project are:

· A robust method based on non-invasive investigation technologies for detecting fault and fracture zones at coal mines, and for assessing the hydraulic characteristics of these structures. This method can reduce the drilling cost for localising the fault structures and testing the conductivity of the structures;

· A rigorous procedure for applying statistical simulations and upscaling analysis to examine the effects of fracture networks on effective hydraulic properties of coal measures, including various methods for data analysis; (applied large fracture zones and faults);

· A computer-based model for simulating the groundwater flow at the study site, which enables the assessment on the effects of fracture zones on the hydraulic connectivity between open cut coal mines and adjacent river and groundwater systems;

· Demonstration of the importance of fault and fracture zones in controlling groundwater flow within the coal mine and ambient water systems; and

· Guideline to assist in identifying, prioritizing and managing the hydrogeological investigation needs on a range of mine life cycle phases.

These outcomes ultimately will assist the evaluation of the mining impact on the rivers and aquifers and associated risks, and help the mines to assess and improve mining feasibility and environmental compatibility. The findings from this project also have implications for open cut coal mines in other parts of Australia.