The Hazelwood mine void is very large, at 6 kilometres long, 3.5 kilometres wide and up to 135 metres deep.
The Hazelwood mine’s size and close proximity to the Princes Freeway and southern part of the Morwell township means that long-term safety and stability are extremely important considerations for its rehabilitation.
ENGIE Hazelwood considers a full pit lake to be the most effective and lowest risk method for achieving a long-term safe, stable, sustainable and non-polluting landform.
Risks of an empty mine void
If left unfilled and unmanaged, the Hazelwood mine void could lead to issues including unsafe ground movement and fire from exposed coal.
There are two main ground movements that are a risk for an empty coal mine void:
1. Floor heave occurs when the aquifers below the mine floor put upward pressure on the empty mine void, causing instability in the mine walls.
2. Coal block movements occur when water from high rainfall events can build up in the gaps between coal blocks. Increasing water pressure can push the coal blocks into the empty void, which can cause the mine walls to move.
The pressure of water from a full pit lake landforms stops the steep sides of the mine void collapsing. This is achieved as the weight of water in the pit lake counteracts the upward pressure from the aquifers below and the inward pressure from the sides.
Pit lake landforms within former coal mines are a common rehabilitation method successfully implemented in a number of mines nationally and internationally.
Understanding land and solid wastes at Hazelwood
Works to rehabilitate the land surrounding the mine void have been ongoing since the mine closure in 2017. Demolition of major infrastructure is now complete, and the project is moving to the next phase of rehabilitation.
Before the decision that an EES should be prepared for the Hazelwood Rehabilitation Project, ENGIE Hazelwood initiated preparation of independent environmental audits across the entire 4000-hectare site.
Regardless of the outcomes of the EES, the site will be rehabilitated to the highest standards.
The land and solid waste study focuses on understanding potential risks related to the creation of a pit lake.