An open-cut coal mine is an enormous intrusion into the environment – and a very striking one. However, with the proper technology at hand, mining companies can ensure that environmental impacts are kept to a minimum and all activities comply with legislative requirements. For this coal mine project in north-eastern Australia, DHI developed rules to optimise mine water release, ensuring compliance with water quality standards and assisting in the project approval process.

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The dispersion of mine discharge into the river

Maryborough is one of the oldest provincial cities in Queensland, with Mary River as its lifeblood. It is situated right next to a major coal mining area, the Burrum Coal Measures. A company with coking and thermal coal projects intended to develop a coal mine in the Burrum Coal Measures, to the north-west of the Mary River estuary. The mine is expected to deliver 0.5 million tonnes per annum of coking coal from an estimated five million tonne reserve.

The company proposed to release excess mine water from the proposed mine site into the Mary River. The area is regarded as one with high environmental value (HEVZ) and the World Heritage Listed Fraser Island is situated just west of the Mary River. Therefore, attention needs to be given to the impact of the mining activities on aquatic ecosystems.

The Mary River water quality model showing water quality variations. ©DHI


On the right track to environmental compliance

Our client submitted an environmental management plan (EMP) to the Department of Environment and Resource Management (DERM). DERM requested more detailed studies on a number of aspects, including water management plans. To carry out the detailed studies, our client commissioned a team including DHI to assess the potential of releasing mine water into the Mary River, based on field monitoring as well as modelling studies. Information was required regarding both the quality as well as the potential effects of the released water in order to be able to obtain a mining permit.

Installation of a water sampler in the Mary River during a field trip. © DHI

Modelling and optimising the dispersion of mine discharge into the river

DHI took a closer look at the mixing dynamics in the river to assess the far-field mixing effects. A coupled hydrodynamic (HD) and advection-dispersion (AD) model was developed using our one-dimensional modelling software MIKE 11 (now MIKE HYDRO River). Concentrations of various elements found in the mine water release were compared with simulated concentrations at the upstream end of the HEVZ and the reduction in concentrations was calculated. Owing to the length of the simulation period, covering 110 years of historical data and the approximately 8 km distance between the discharge point and the HEVZ, one-dimensional modelling was sufficient to provide a good estimate of the concentration of various elements in the area of interest.

Modelled reach of the Mary River, the mine discharge point and the location of the upstream end of the High Environmental Value Zone. © DHI


Operational rules form the base of professional decisions

The modelling results revealed that the major reduction in tracer concentration occurs at the discharge location. Based on these findings, an operational rule was developed to ensure that water quality was maintained within acceptable threshold values. Mine discharge can now be optimised to fulfill the legislative requirements and minimise impacts on the environment. Our client was also able to submit a revised environmental management plan for the proposed mine.

Preserving Maryborough’s heritage for years to come

Tourism – particularly activities on the Mary River – plays a significant role in the economy of Maryborough; and so will the coal mine project. There were concerns about the development of the coal mine damaging the recreational value of the river. Thanks to DHI’s assessment, our client is now able to develop the necessary operational rules to continue with its mining activities while protecting Mary River’s natural heritage for future generations.

Compliance with water quality standards and better protection of the local environment

Professional decision support for controlled
mine water release

An environmental management plan
complying with legislative criteria

About the client

A coal mining company

Software used

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