“A big part of the discussions was the possibility of using mine voids for the reservoirs of the pumped hydro plants.
While council aren’t disclosing where the site would be for the facility, they have said that an option might be near the Muswellbrook Coal site using a mine void for a lower reservoir.”
https://www.981powerfm.com.au/news/...-hydro-energy-storage-project-in-muswellbrook