Sydney’s sewage outfalls worth $2 billion in social value

Sydney Water has saved residents 180,000 annual sick days and provided $2 billion in social value since decommissioning its cliff-face sewage outfalls in the early 1990s, a Deloitte Access Economic report has found.

The study was commissioned to mark 25 years since the Deepwater Ocean Outfall Program became operational at North Head, Bondi and Malabar – plants which now treat 80% of Sydney's sewage.

“When you talk to people that used to surf at Bondi, Malabar and Manly back then, they took it for granted that you'd dive into a brown sludge or a greasy fatty sludge,” Sydney Water Senior Media and Public Relations Advisor Peter Hadfield.

“One of the stats from the report I was amazed by is that because of all of the ear and throat infections that used to be caused by water quality … [with the deepwater outfalls] you're looking at an estimated saving of around 180,000 sick days, worth about $140 million in avoided absenteeism, every year.”

The report found the deepwater outfalls, which send treated sewage two to four kilometres offshore, have improved water quality at Sydney's beaches, providing a range of economic and social benefits.

“The net value-add associated with beach water quality is around $332 million a year to the New South Wales economy through domestic and international tourism, and the provision of 3500 jobs,” Hadfield said.

“In terms of brand value, the report shows that beaches rank in the 'top three' when visitors think of Sydney – they're thinking about Sydney Harbour, the Sydney Opera House and then they're thinking about the great water quality of our beaches.”

The total value of Sydney’s coastal beaches to its residents is around $1.3 billion each year, of which $130 million is attributable to water quality, Deloitte said.

The three deepwater ocean outfalls cost $310 million to investigate, design, construct and commission. Construction involved a unique combination of tunnelling and offshore engineering technologies.

The outfalls use multiple diffusers to disperse treated wastewater over an area of several hundred metres squared, at a depth of up to 80m.

At the time, the hydraulic design of the outfalls represented the leading edge of development for high dilution, self-cleansing and essentially maintenance-free outfall facilities.

“There were a few other outfalls internationally at that time of a similar design but they haven't worked as efficiently as our Sydney deep ocean outfalls have,” Hadfield said.

“[That's] because of the unique aspects of the coastline ... it drops off into deep water very quickly and there's some extremely strong currents off those three outfalls [which means] nature is doing an absolutely wonderful job in treating that wastewater.”

Hadfield said that footage taken when the outfalls were first turned on showed an immediate improvement.

“You could see from the film footage that there was a brown smudge heading out from the Bondi cliff-face and as soon as the Premier switched it on, it actually cleaned up within a couple of minutes,” Hadfield said.

“There was some speculation that we were moving a problem offshore but in fact our six-monthly inspections of the deep ocean outfalls, testing of nearby sediment and species biodiversity shows that's not the case.”