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The Dandenongs have a dirty secret. An environmental time bomb has ticked for decades, but is now making itself visible: patches of lush, ferny mountain forest are dying off.
Each day, 12.7 million litres of waste water and human waste is discharged into streams and delicate ecosystems in the ranges. The main culprits are 10,000 unsewered homes, with septic tanks that fail, are not maintained or are too old. Studies have connected the nutrient-rich waste with the die-back of forest, mostly in the Dandenong Ranges National Park. Mature mountain ash, their roots poisoned and water-logged, have been among the victims.
But Parks Victoria staff were particularly alarmed when their regular testing of Kay's Spring near Kallista - where people have collected spring water for years - found early last year that the water was unfit for human consumption. The ground water had been contaminated.
The Shire of Yarra Ranges says the situation is critical. "The thing with the Dandenong Ranges is that it looks green and lush, but it is just a time bomb waiting to go off," said Sophie Akers, the shire's waste water project officer. "It's really scary that you've got that sort of activity going on in national parks. We've got all this old infrastructure that is basically failing," she said.
The Dandenongs's 48,000 residents rely on septic tanks because most of the area has no sewerage - authorities have ruled it out on a large scale because of tree damage and landslide risk. Many houses were built when the discharge of grey water - from bathrooms, laundries and kitchens - was permitted. It runs into drains and ends up in creeks.
The shire says many residents do not maintain or replace their septic tanks, leading to raw sewage finding its way to creeks. Development has also meant more dishwashers and spas, and therefore more water discharging into the sodden environment.
Waterlogging increases the risk of landslip, Ms Akers says. "People are living in landslip-prone areas and water is discharging off properties basically into unstable soils. It can only retain a certain amount of water before you have a landslip."
The shire is bringing together experts to find solutions tailored to the Dandenongs. It hopes residents will opt for waterless or composting toilets, use communal treatment plants to filter waste water and empty their septic tanks every few years.