Mine Water Filling Strategy

Anglesea mine pit aerial

The key remaining aspect of the Draft Mine Rehabilitation and Closure Plan is an approved strategy to fill and maintain the mine pit with water. While we have investigated a range of potential options to support filling the mine pit in a timely manner, an approved strategy remains outstanding.

We acknowledge the importance of this matter to the community and will continue to engage as we undertake investigations to deliver the best possible outcome for the future of the site, the community and the environment.

About the Strategy

Approximately 18 gigalitres of water is needed to fill the mine pit. As of April 2025 there is approximately three and a half gigalitres of water present.

Our preferred option is for a fast fill strategy to fill the mine pit over seven to ten years by supplementing the natural filling of the mine with a combination of Upper Eastern View Formation groundwater and peak flows from Salt Creek.

The fast fill strategy is currently subject to a groundwater licence amendment application (details below), however no active work is being undertaken on the option to use peak flows from Salt Creek as this will be determined as part of the final Mine Rehabilitation and Closure Plan.

This strategy will support a critical fire break to minimise the fire risk to the Anglesea township and potential benefits to the environment, the regional economy and the community from the future land use of the rehabilitated landscape.

The alternative is to continue with a natural fill, which is expected to take many decades and will not support the broader outcomes expected by the community and government in a timely manner.

The strategy is independent of whether the Eden Project Anglesea concept or other future land use concepts are realised.

Groundwater Pumping Test

In 2021 we completed a groundwater pumping test to provide Alcoa, regulators and the community with science-based information to determine whether groundwater can be used to fill the mine pit without adverse impact on groundwater dependent ecosystems, including the Anglesea River.

The rigorous process was overseen by Victorian government agencies and departments. Importantly, the data gathered during the pumping test did not identify any adverse impacts on groundwater dependent ecosystems, including the Anglesea River.

During the test regular updates were provided to the community and key stakeholders. Those published updates can be seen here.

The test was undertaken by expert hydrogeologists, with oversight by a co-regulator technical working group comprising representatives from Southern Rural Water, Department of Energy, Environment and Climate Action (DEECA), Corangamite Catchment Management Authority, EPA Victoria, Earth Resources Regulation and Barwon Water.

The data retrieved was used to update the Anglesea Groundwater Model in conjunction with Barwon Water and was independently reviewed by a Technical Review Panel established by DEECA.

Together with the Anglesea Groundwater Model, the data was also used to inform a groundwater impact and environmental risk assessment undertaken by Alcoa. This revealed a sustainable pumping rate that does not adversely impact groundwater dependent ecosystems, including the Anglesea River, can be achieved.

Groundwater Licence Amendment Application

Alcoa submitted a formal groundwater licence amendment application with Southern Rural Water in July 2024 requesting approval to pump groundwater from the Upper Eastern View Formation (UEVF) to fill the mine pit in seven to ten years.

The amended application seeks approval from SRW to reduce our existing groundwater licence from 4 gigalitres per year to 1.5 gigalitres per year, and amend its use to allow groundwater to be used to fill the mine pit, which is estimated to take seven to ten years.

While the risks of adverse impact on the environment are already low, applying the precautionary principal is a conservative approach, being less than 40 per cent of the historical extraction rate ensuring an even lower risk approach.

If approved, the licence will enable Alcoa to accelerate return of the former mine and power station site to the community consistent with the draft Mine Rehabilitation and Closure Plan, while providing long-term environmental benefits sooner, in contrast to a natural fill approach, which is expected to take many decades.

The decision to submit the licence application was made following consideration of feedback received during three well-attended community open house sessions and is backed by more than four years’ technical work.

To ensure the reduced and amended allocation poses no unacceptable risks to the environment that may rely on the groundwater, a Groundwater Impact Assessment (GIA) has been prepared supporting this application for SRW’s assessment.

The GIA considers multiple sources of data and lines of evidence including:

  • Review of multiple independent technical studies completed relevant to groundwater use and potential impacts (e.g. Maher 2011)
  • Numerous Alcoa studies relevant to groundwater use and potential impacts
  • Detailed assessment of long-term water level, water quality, climate and surface water flow observation data from more than 130 groundwater monitoring points and available surface water flow sources
  • The 2021 Alcoa Groundwater Pumping Test that was subject to regulatory oversight and showed no adverse impacts on groundwater dependent ecosystems including the Anglesea River or other users
  • Significantly improved conceptual hydrogeological model for the Alcoa area of interest which has been subject to, and endorsed by the regulator Inter Agency Group appointed independent Technical Review Panel (TRP)
  • The updated 2024 Anglesea groundwater numerical model (in conjunction with Barwon Water), which has also been subject to and endorsed by the TRP comprised of independent experts
  • Hydrogeological risk assessment including for proposed Alcoa groundwater extraction, including applying the relevant medium and high climate change models
  • The feedback from on-going and community engagement processes and events including the open house events in May 2024

The GIA is based on long-term water level, water quality, climate and surface water flow observation data that has formed a well-established and understood baseline of conditions across the catchment. Importantly detailed analysis of this data indicates there has not been any adverse impact of groundwater extraction in the past on environmental receptors.

Despite the overall low risk and conservative approach, Alcoa recognises that the river system (Alluvial Swamp Aquifer (ASA)) is a sensitive receptor, and that any activity including groundwater extraction does present a risk – albeit low as described in the GIA.

In response, and to monitor for any potential risks, Alcoa are also proposing that one of the key conditions of any amended groundwater licence should be an updated adaptative management and monitoring plan, including trigger levels and actions.

This would help ensure that, in the event any potential (but unexpected) impacts occurred, they would be detected early, and appropriate action could be taken including ceasing the activity – reducing the current low risk even further.

Read the Alcoa Anglesea Groundwater Impact Assessment in its entirety.

Southern Rural Water Assessment

Southern Rural Water are responsible formally assessing our groundwater licence amendment application submitted to the regulator in July 2024.

The assessment process, facilitated by SRW, includes:

  • A public advertisement and comment period
  • An open house session
  • A subsequent online submission hearing for those who provided a submission

The purpose of this consultation is to give community and stakeholders an opportunity to provide feedback to Southern Rural Water on our amendment application.

Southern Rural Water is responsible for regulating groundwater in Southern Victoria under the Water Act 1989.

For more information on the groundwater application process (including commencement dates) and how to make a submission, visit srw.com.au.

The application forms part of Alcoa’s ongoing efforts to finalise an approved mine water filling strategy to fill the mine pit in a timely manner and subsequently accelerate the return of the site to the community.

Discussion Board

We have listed the top questions asked about the mine water filling strategy below. If you have a question about the strategy or any other aspect of our rehabilitation activities, please email angleseaps@alcoa.com.au.

Throughout the project we have investigated a wide range of options to support filling the mine pit in a timely manner including restoration of Salt Creek, recycled water, Lower Eastern View Formation (LEVF) groundwater, seawater and desalination.

Investigations and modelling into a natural fill have indicated it may take many decades to fill. During this time community access to the area would remain restricted.

The only current feasible options are the potential use of Upper Eastern View Formation (UEVF) groundwater or natural fill.

Our investigations have involved comprehensive scientific and technical testing to ensure the approach is responsible, best addresses environmental considerations and delivers the best community outcomes.

The GIA has been developed to evaluate what impact (if any) Alcoa’s reduced and amended allocation proposal would have on the environment. It is a highly technical and comprehensive analysis of all available lines of evidence used to determine any potential risks on groundwater dependent ecosystems including on the Anglesea River. The lines of evidence are listed in the text to the left of these FAQs, under the heading Groundwater Licence Amendment Application.

A GIA is required to support any groundwater licence amendment process, is a key part of the submission made by Alcoa to Southern Rural Water, and is a culmination of more than 4 years of technical work and regulatory oversight.

It has been developed using multiple lines of evidence including long-term water level, water quality, climate and surface water flow observation data and has resulted in a well-established and understood baseline of conditions across the catchment.

Importantly analysis of the multiple lines of evidence and data has not shown any adverse impact of groundwater extraction in the past on environmental receptors, not with the proposed license amendment.

After more than 4 years of technical work and investigation, including multiple independent assessments, and consideration of multiple lines of evidence, the proposed groundwater licence amendment presents a low risk of adverse impact to the environment.

Despite this, Alcoa recognises that the environment including the Anglesa River (Alluvial Swamp Aquifer - ASA) is a sensitive receptor, and that any activity including groundwater extraction does present a risk – albeit low as described in the GIA.

In response, and to monitor for any potential risks, Alcoa are also proposing that one of the key conditions of any amended groundwater licence should be an updated adaptative management and monitoring plan, including trigger levels and actions and regular reporting to the community.

This would help ensure that, in the event any potential (but unexpected) impacts occurred, they would be detected early, and appropriate action could be taken including ceasing the activity – reducing the current low risk even further.

We have a regulatory obligation to develop the final Anglesea Mine Rehabilitation and Closure Plan. The mine water filling strategy is independent of whether the Eden Project Anglesea concept or other future land use concepts are realised.

We have undertaken extensive technical work to assess the feasibility of using groundwater to fill the mine pit.

Spanning almost four years, this rigorous process has included analysis of hydrogeological models, actual historical data, independent technical studies and groundwater pumping tests as well as the development of a groundwater model in conjunction with Barwon Water. These have all confirmed the proposed extraction would have no adverse impact on groundwater dependent ecosystems, including the Anglesea River.

Similarly, historical studies commissioned by Victorian government agencies determined our operations have had no negative impact on the health of the Anglesea River.

We understand the health of the Anglesea River is an important issue to the community.

Throughout mine rehabilitation and closure works, rigorous scientific and technical testing has been conducted to ensure our chosen approach is environmentally responsible and safe for the community.

Results of this testing and analysis indicate that the acidity of the Anglesea River is influenced by naturally occurring factors.

Soil surrounding the river and the peat swamps within the river catchments naturally contain acid sulphate materials. During periods of drying and heavy rain, water flows through the soil and peats and into the river - affecting its pH levels.

Our activities have been subject to many independent technical studies and all have found that we have had no adverse impact on groundwater dependent ecosystems, including the Anglesea River.

Creation of a water body benefits the environment, the regional economy and the community. It also creates a critical fire break to minimise fire risk to the Anglesea township and assists geotechnical stability through the weight of water at the base of the mine.

Over 30 million tonnes of soil would be needed to fill the mine pit. Sourcing and transporting this large quantity would create significant environmental and safety issues.

Filling the mine pit with soil would also remove the fire break that the mine now in part provides the township of Anglesea (a recommendation from the 2015 Anglesea Hazelwood Mine Fire Inquiry).

We hosted a mine site tour for members of the RMIT team to help inform their Regenerative Transformation Lab concept. We continue to stay informed about possible future land uses for the area through this and other interesting concepts.

Under our regulatory obligation, we are focused on finalising an appropriate mine water filling strategy to deliver a final Mine Rehabilitation and Closure Plan.

Following successful rehabilitation of the former mine area, this large portion of land will be returned to the State who will determine its long-term use.

We are committed to achieve this in a way that enhances and protects the environment, does not preclude any appropriate long-term uses and is in line with Alcoa’s guiding principles developed with the community.

This will enable the State to make decisions regarding use of the area which we believe will be consistent with the Anglesea Futures Plan (DELWP) published in 2018.

While Alcoa has not provided a written response to Professor Ralf Haese, our team and hydrogeologist have discussed the paper at length over many collective hours with the Professor and representatives from the Friends of Anglesea River group.