Just months after the NSW government spent $1.26 million reopening two new swimming sites along Parramatta River, Sydney Water is proposing to pump 70 million litres of treated wastewater into the river every day.
It would be enough to fill around 35 Olympic-sized swimming pools daily.
The proposal is for a new wastewater treatment plant to be built in the city's west at Camellia-Rosehill by 2032, connected by a 5.3-kilometre largely tunnelled pipeline to a river outlet at Meadowbank Park.
Project delivery lead Caine Mertens told the ABC the highly treated wastewater would be cleaner than the current river water and would improve local water quality.
"Water in this project will be treated to a very high level with lots of safeguards, lots of redundancy."
New infrastructure needed to meet population growth
Sydney's Northern Suburbs Ocean Outfall Sewer and the North Head Water Resource Recovery Facility currently process wastewater for approximately 1.7 million people across the city's western and northern suburbs.
However, Sydney Water said this existing infrastructure would reach capacity by 2031.
It said the Camellia-Rosehill facility was needed to meet the needs of the additional 230,000 people forecast to live in the area over the next 30 years.
"This is all about relieving that pressure on our wastewater system," Mr Mertens said.
Ian Wright is a former Sydney Water scientist who spent 18 years with the company, and is now an associate professor and water science researcher at Western Sydney University.
He said treating raw effluent reliably was difficult, and expressed concern with the proposal.
"Pumps break, filters block. All kinds of things can happen, so you may be able to achieve high quality most of the time, probably not all the time."
The project is being assessed as a state significant development application by the Department of Planning, Housing and Infrastructure.
'We're very concerned'
Sydney Water, local councils and the state government over recent years have made efforts to improve water quality to establish swimmable sites along Parramatta River.
Just last year, the NSW government spent $1.26 million opening two new local swimming sites at Bedlam Bay in Gladesville and Putney Beach.
They are both located several kilometres downstream of the proposed Meadowbank outlet, but the area is also home to a thriving ecology of mangroves, wetlands and wildlife.
"Water quality in the Parramatta River is not that good, the locals know that … Personally, I do swim in the river, but I keep my head out," Professor Wright said.
Sydney Water said swimability would not be impacted by the proposal if approved.
"Our assessments have tested both water quality at the discharge spot and at locations downstream, including swimming spots, and the investigations we have done show that water quality will be improved at those spots over the time," Mr Mertens said.
The riverside banks of Meadowbank are home to endangered migratory birds and wetlands, still recovering from decades of industrialisation.
Sydney Water's proposal has already received more than 400 public submissions, with most highlighting concerns around environmental and wildlife impacts.
Local resident Andrew Yeung shared his concerns, given the area's high recreational use.
"We've got swimming areas, three downstream, and a junior sailing club, as well as three boat ramps," he said.
"We're very concerned about potential for a combination of factors heading over a tipping point and creating an environmental disaster.
"This is an endangered migratory bird habitat … we had millions of baby prawns just behind me for months," he said of the nearby wetlands surrounding Sydney Olympic Park, which are connected to Parramatta River.
Safety control measures
Sydney Water said the proposed facility would have several fallback mechanisms.
"Any off-spec water can go back to the existing system, and only high-quality water will go to Meadowbank," Mr Mertens said.
The organisation said the fallback mechanism for water quality issues still requires someone to manually override the system.
"If it's a water quality piece, it's a manual override by our operators. If it is a power outage, then that is managed through our control system," Mr Mertens said.
Before any water can be released into Parramatta River, Sydney Water must obtain an environmental protection licence (EPL) by the NSW Environmental Protection Authority (EPA).
"The EPA has been very clear on their requirements for us for this project," Mr Mertens said.
Under current NSW planning laws, the EPL would not be issued until after the project is approved and prior to any discharges occurring.
The EPA said in a statement it considers a range of factors when setting license limits, which it said is in line with the Protection of Environment Operations Act 1997.
"The EPA will set licence conditions, including discharge limits, based on information in the proponents' Environmental Impact Statement, EPA policies and guidelines and considering the characteristics and uses of the receiving environment," it said.
Location supported, Sydney Water says
Professor Wright described Parramatta River as "a very sick waterway".
"For me the worst case is 70 megalitres a day having a major breakdown in the system and releasing raw effluent, and that is plausible, it does happen from time to time," he said.
"Because it's tidal, it'll slosh between Parramatta River and the Opera House … it's unlikely, but there is the possibility that it could happen."
Sydney Water said Meadowbank was selected as the preferred release site after assessing several locations.
Depth readings conducted by Sydney Water and provided to the ABC show Meadowbank is only marginally deeper (4.2 to 5.1 metres) than a rejected site at Wentworth Point site (4.2 to 4.9 metres).
Two other proposed locations at Bedlam Point and Pulpit Point, were up to four times as deep.
"Depth was one of several criteria used to assess suitable river outlet locations," Sydney Water said.
The organisation said it also engaged with a total of nine independent experts to provide specialist advice on the proposal.
Sydney Water said it engaged with 185 community members across six events and would now begin the process of responding to submissions.
It then plans on working with contractors to finalise details for construction.
