Yallourn Coal Mine Inquiries
Review of the Morwell River diversion failure
On 5 June 2012 an embankment built to divert the Morwell River through the Yallourn mine developed a leak which got larger over the following hours and ultimately led to the failure of the structure on 6 June 2012.
Subsequently, the Department commenced a formal investigation under the Mineral Resources Sustainable Development Act (MRSDA) to determine both the root causes of the failure and whether there has been any breach of statutory requirements on the part of the mine operator.
This is standard practice after an incident of this nature and will help prevent further similar incidents in future and assist the Department in assessing any long-term solution to the river diversion.
The investigation team, comprising a DPI Lead Investigator and an external geotechnical expert with experience in civil construction structures completed their investigation in May 2013.
The key findings in the report noted that the key causes of the failure were considered to be:
- The use of dispersive clays in Zone 1B, underlying the flood plain
- The incidence of cracking in the flood plain due to a combination of drying / shrinkage effects and differential settlements in both longitudinal and transverse directions
- The filter design (some of the sand used was too coarse to protect the dispersive clays in Zone 1B)
- The filter location (not in accordance with normal convention)
- Sole reliance on a membrane seal over the joints in the conveyor tunnel elements..
The executive summary of the report is available
Please contact the Customer Service Centre on 136 186 to obtain a full copy of the report.
Collapse of the Morwell River Diversion at the Yallourn Mine, June 2012: what happened?
In early June 2012 there was a collapse of an embankment of the Morwell River Diversion into a section of the TRUenergy coal mine at Yallourn, following significant rainfall into a swollen catchment.
In the hours prior the collapse, the Diversion was close to capacity. Water was reported leaking from the roof of tunnels located at the base of the earthen structure. The tunnels were built to transport coal beneath the Morwell River diversion from the mine pit to the generators.
How is river water quality being protected?
Water being pumped from the mine to the Latrobe River is monitored by the Environment Protection Authority (EPA) in accordance with Victoria’s strict water quality regulations.
The EPA requires TRUenergy to monitor/sample waterways three times a week and report these back to EPA.
Companies with EPA monitoring requirements are required to use an independent, National Association of Testing Authorities (NATA) accredited laboratory to take and test the samples.
If the results provided by a business are found to be outside the parameters specified by a site licence or regulation, EPA will undertake its own sampling and testing and investigate further.
EPA has issued a publication on their activity.
What is the Department’s role?
Departmental mining and geotechnical engineers have regularly been on site at Yallourn to manage the recovery operations, provide technical advice and facilitate any required government approvals.
Is this connected to the previous incident at Yallourn in November 2007?
At this stage there is no proven connection between the two incidents.
The 2007 incident involved batter wall movement, whereas this event involved a constructed embankment.
Who approved construction of the Morwell River diversion?
Approval of the project was subject to an extensive Environment Effects Statement (EES) in 2005.
An Independent Panel of technical advisors was appointed by the then Minister for Planning to provide the Minister advice on if they should approve the project.
Once planning approval was in place, DPI approved a variation in the Work Plan in relation to the extension of the mine which included the design and construction of the diversion.
This was independently peer-reviewed at several key milestones:
- prior to construction starting,
- once the embankment wall had been completed and
- once the conveyer belt tunnels had been completed.
What is the difference between the role of the Department in regulating/monitoring operations at Victorian mines and the obligations of the mine operator?
A company is responsible for the day-to-day operations of a mine and to ensure compliance with legislative requirements and ensure that the mine area is stable and safe.
It is the role of the regulator to conduct regular audits and physical inspections of mine operations.
What approvals have the Department given Yallourn for remedial work?
To date the Department has granted two approvals to divert Morwell River flow - to allow for work to remediate the Morwell River diversion – firstly approval was granted to divert the river into the Township coalfield immediately following the diversion collapse and more recently in the Eastfield mine area.
Are the roads / rail lines adjoining the mine safe?
TRUenergy is actively monitoring stability across the mine and the Department is oversighting this monitoring activity.
Departmental geotechnical and hydrogeological experts are reviewing the monitoring data provide by TRUenergy. The monitoring program around batters located adjacent to roads and rail lines has increased from weekly to daily monitoring of movement and ground water levels and daily inspections. The results indicate no impact on public infrastructure.
What happens next?
As a temporary solution, TRU energy is installing pipes across the breach area to take low flows until the Morwell River diversion is remediated. Long term solutions are in development.
Release of Mining Warden Report and Government Response to the Yallourn Mine Batter Failure
A mine batter in the Yallourn East Field failed on 14 November 2007. On 4 December 2008, Mining Warden Prof. Tim Sullivan, tabled his report into the facts circumstances and causes surrounding the failure of the mine batter.
The main elements of the government response at the time were :
- Development of a cross-agency water co-ordination group
- Greater coordination of Latrobe Valley regional mine planning
- Establishment of a Technical Review Board
- Strengthened DPI capacity & capability
- Review of Latrobe Valley coal mines with respect to geotechnical and hydrogeological risks
- Ongoing education for industry and government officers and other stakeholders
- Encouraging research and development in relation to geotechnical and hydrogeological aspects