Six reservoirs near Melbourne record PFAS detections

Six drinking water supplies located to the west and north west of Melbourne have had PFAS chemicals detected in them over the past 16 months according to a Freedom of Information request from Greater Western Water. All detections were recorded in raw water, however treatment methods at water treatment plants often have limited success in removing PFAS and apparently no testing was conducted on the drinking water itself. It appears that Greater Western Water only started testing for PFAS chemicals in drinking water supplies in July 2023.

The impacted reservoirs include Djerriwarrh Reservoir and Merrimu Reservoir (located north of Melton), Wright Reservoir and Brock Reservoir located south east and east of Woodend and Garden Hut Reservoir located west of Lancefield, as well as the Lancefield Service Basin. The August 2023 event at Djerriwarrh represents the highest PFAS loads in any Victorian water supply.

The most serious incident occurred at Djerriwarrh Reservoir in August 2023, when eight separate PFAS chemicals were detected. The sum of PFAS detected during this event was 210ng/L. Included in the 210ng/L was a detection of PFOS at 53ng/L and PFHxS at 4ng/L. Combined, this event would be about 81% of the current Australian Drinking Water Guideline (ADWG), which combines PFOS and PFHxS. However recent proposed changes to the ADWG by the National Health and Medical Research Council would see the safe guideline for PFOS reduced to 4ng/L and PFHxS reduced to 30ng/L. This means that the 53ng/L PFOS detection is 13.25 higher than the proposed new guidelines. The Djerriwarrh incident represents the highest levels of PFOS detected in a Victorian supply. 

Djerriwarrh was tested again two weeks after the positive results and came up with no detections above the level of detection. Lower levels of PFOS 3ng/L and 5ng/L were also detected in Djerriwarrh Reservoir in February and March 2024.

The burning question that needs to be asked is, how did such high levels of PFAS chemicals enter Djerriwarrh Reservoir, when most of the Djerriwarrh catchment is forested? Has fire fighting foam been used in the catchment at some time to put out a bush fire? Is the PFAS coming from upstream of the forest by landowners living south west of Gisborne? Nearby Merrimu Reservoir also recorded PFAS chemicals in December 2023 and May 2024. The main PFAS chemical detected at Merrimu was PFBA.

A total of 27 PFAS detections were recorded by Greater Western Water out of 6892 samples conducted between July 2023 and October 2024. 142 of the test results are still pending, meaning that 0.4% of the tests conducted by Greater Western Water were positive for PFAS.

The highest PFAS loads detected by Greater Western Water are the short chain PFBA and PFHpA. The Australian drinking water guidelines currently only have guidelines for PFOS, PFHxS and PFOA. The new proposed guidelines for PFBS will probably appear in 2025. For PFBA, PFHpA, PFPeA and PFHxA we could be waiting many years for PFAS guidelines. So what is a safe level?

Of all the PFAS chemicals detected by Greater Western Water, PFOS is the most toxic. The highest levels were recorded at Djerriwarrh. PFOS was also detected at Wright Reservoir and Brock Reservoir which supply drinking water to Woodend. PFBA was mainly detected at Djerriwarrh and Merrimu, with PFHpA detected mainly in the Lancefield system, particularly in Garden Hut Reservoir on Deep Creek. Again what was the source of the PFHpA in the Deep Creek catchment. Who is investigating why it was there?

In terms of potential drinking water supplies impacted by PFAS in the Greater Western Water network, Djerriwarrh Reservoir and Merrimu Reservoir can be used to supply Bacchus Marsh, Darley, Long Forest, Melton, Melton South, Rockbank and Toolern Vale. These communities are also connected with the Melbourne supply system which has apparently recently recorded PFAS in it.

Lancefield can receive its drinking water from Garden Hut Reservoir, bores near the town, water from Rosslynne Reservoir, Romsey and the Melbourne supply system.

Woodend can receive its drinking water from the Campaspe Reservoir, Graham Brock Reservoir, Mount Macedon Reservoirs, Rosslynne Reservoir and the Melbourne supply system.

What this means is that it is most likely that whatever PFAS chemicals were detected in the system, they are most likely to have been reduced significantly by 'shandying' of the impacted water, with non-PFAS tainted water or shutting off the particular contaminated source.

The Freedom of Information request also request information on pesticides detected in the water supply system. No detections of the 10 pesticides that Greater Western Water tested had occurred between 2017-2024.

Contact Anthony Amis 0425 841 564 for more information