Low pH in Boundary Creek and Barwon River
The source of the low pH is likely to be acid-sulfate soils in Big Swamp that have previously dried out and then been soaked by heavy rainfal.
Community members living along Boundary Creek and the Barwon River (near Birregurra) have been advised of a temporary change to water quality in local waterways.
Monitoring has detected pH levels in Boundary Creek of 3.4. Low pH levels between 4.8–5.2 were also recorded in the Barwon River near Birregurra, downstream of Boundary Creek.
People are advised to avoid direct skin contact with the affected water until further notice as this may cause eye or skin irritation. There is no impact on drinking water.
pH likely linked to acid-sulfate soil flushing
The source of the low pH is likely to be acid-sulfate soils in Big Swamp that have previously dried out and then been soaked by heavy rainfall, flushing acidic water into Boundary Creek.
Barwon Water launched a series of technical studies and an enhanced groundwater monitoring program in 2012. Results of two studies were released publically last year, with the scientific data confirming the interaction between groundwater pumping at the Barwon Downs borefield and nearby Boundary Creek and Big Swamp.
The data showed the operation of the Barwon Downs borefield over the past 30 years is responsible for two-thirds of the reduction of base flow into Boundary Creek. The dry climate experienced during the same period accounts for the remaining third. Studies also confirmed drying of Big Swamp has resulted in activation of acid-sulfate soils and subsequent releases of acidic water into Boundary Creek.
The data is crucial as it provides a solid scientific basis for us to develop options to improve the condition of Big Swamp and minimise acid events in Boundary Creek in the future. We are absolutely committed to remediating the swamp to improve water quality and flows in the creek.
We recently formed a community and stakeholder working group to develop a remediation plan for the swamp and the creek. The group is working together over the coming months to assist us in designing and implementing a remediation plan for the creek and swamp.
The group includes community and stakeholder representatives from the Corangamite Catchment Management Authority, Colac Otway Shire Council, Land and Water Resources Otway Catchment, People for a Living Moorabool, Upper Barwon Landcare Group, Boundary Creek landowners, Traditional Owners and community members.
The group will work together to assist Barwon Water in designing and implementing a remediation plan for the creek and Big Swamp, with the goal of returning the creek to a healthy ecosystem.