Groundwater Monitoring
Mindarie Regional Council (MRC) has carried out groundwater monitoring at Tamala Park since 1998, with the purpose of:
- Detecting leachate reaching the groundwater;
- Determining the direction of groundwater flow;
- Assessing the quality of the groundwater; and
- Determining the migration of any leachate plume.
What is leachate?
Leachate is the term used to refer to rainwater which has travelled down through the top of a landfill and into the landfill mass. It can also refer to the liquid waste produced when organic material breaks down within the landfill mass.
Leachate is found in all landfills, and its management is a key consideration for any landfill operator.
Why does MRC undertake groundwater monitoring?
The first phase of the Tamala Park landfill was conducted in an 'unlined cell'. This means that landfilling took place without a liner (an impermeable geosynthetic barrier) being installed underneath. Therefore, in this part of the landfill, it has not been possible to entirely contain and manage leachate. This practice was approved at the time. All subsequent phases of the Tamala Park landfill have been lined.
The WA Department of Water and Environmental Regulation requires MRC to periodically commission an independent review of potential issues resulting from the Tamala Park landfill through a Mandatory Auditor's Report, or MAR. This independent review includes analysis of MRC's groundwater monitoring methods and is prepared by a DWER accredited auditor.
The latest MAR was presented to the regulator in Autumn 2025.
What does the MAR conclude?
The report identifies the extent to which leachate from the Tamala Park landfill is affecting the groundwater. It also concludes that the type and level of monitoring currently undertaken by MRC is appropriate. Finally, it recommends - to the regulator - areas in which MRC might be able to supplement its current monitoring methods.
Based on the current understanding outlined in the report, there are no recommended remediation works required of either MRC, nor Catalina Regional Council (CRC), which manages the land immediately north of Tamala Park.
DWER has stated that it accepts and agrees with the independent auditor's report.
MRC accepts the report's findings and is committed to actioning its recommendations in accordance with the guidance provided by the regulator. MRC will continue to monitor the groundwater in alignment with DWER's requirements.
The report has has not identified any immediate risk to human health. This view is consistent with MRC’s own view on the matter.
A copy of the latest Mandatory Auditor's Report can be found below:
Mandatory Auditor's Report.