Narrow escape from water release at Dargues gold mine

The recent heavy and sustained rains have put pressure on the Water Management System at Dargues gold mine near Majors Creek. The tailings dam reached maximum operational capacity on Wednesday 9 March, so Aurelia Metals shut down the processing plant to stop the flow of tailings into the dam to minimise any further rise in water levels. The rain has now stopped and there was no overflow from the dam.

The company engages with community stakeholders through the ‘Dargues Mine Community Consultative Committee’ which meets quarterly. However, because of the recent heavy rains a special meeting was held this week (Wednesday 9 March) to share information about the impact the rainfall has had on the mine and the water management system, and environmental effects. The committee includes representatives of the Majors Creek and Braidwood communities, downstream users along the Deua and Moruya Rivers, Eurobodalla and Palerang Shire Councils, and The Coastwatchers Association.

So far all contaminated water has been contained and none released into the environment. Surface water is diverted around the mine and joins local gullies and creeks from surrounding farmland which have been flowing heavily, resulting in very turbid flows into the headwaters of the Deua River. The water level in the tailings dam rose steadily during the East Coast Low weather system, reaching just 400 mm below the spillway level on 9 March. The company put measures in place to reduce the risk of the tailings dam overflowing. These include:

• processing of ore stopped so that no tailings are pumped into the dam;

• contaminated water collected at the processing plant site has been transferred to the underground workings;

• maintenance and minor modifications to the diversion bund which diverts water in gullies etc away from the tailings dam and into the Majors Creek system below the mine workings;

• fortified the spillway with extra rock to reduce the likelihood of erosion if a spill was to occur.

The good news is that there has been no overflow from the tailings dam into the environment, and with the break in weather a spill from the tailings dam is likely to be avoided. (When ore processing recommences, it will consume more water from the dam than is pumped in with the tailings, so it has the effect of reducing the water level). However, if more heavy rainfall occurs in the next few weeks, other measures will need to be considered. The company is currently discussing options with the EPA and specialist consultants.

Longer term options already in the planning phase include raising the tailings dam wall by 4 metres, and constructing a 'turkey's nest dam' to contain excess tailings dam water; however, these will take months to construct and to bring into operation. (A turkey’s nest dam is one not constructed in a water course).

At the community consultative meetings it has been made clear to the company that the preferred outcome is to avoid any release of water from the tailings dam into the environment, and we are very pleased that a water release was avoided during this extreme weather event. However, the extent of the recent rains, and the probability of more intense events in the future as the effects of climate change become more established, suggest that the mine will need to develop strategies to provide a higher level of protection against discharge from the tailings dam into the future.

The downstream users and The Coastwatchers Association constantly press for a focus on protection against release of contaminated water, and recent events will ensure that this pressure will be maintained. The company has undertaken to engage with the community consultative committee more frequently as data on the weather event, water chemistry data, and options to reduce the risk of environmental releases of contaminated water come through.

Stewart Needham

The Coastwatchers Association

View over the tailings dam in December 2021, before the East Coast Low rain event. The water level is several metres below the overflow spillway (which is halfway along the dam wall on the left). The black material is an impervious membrane below the tailings. The track around the dam follows the crest of the diversion bund which directs overland flow away from the dam and into Spring Creek below the mine area.