Along the banks of the Ohio River on Pittsburgh’s North Side sits a piece of local history that goes largely unnoticed by most.
Well—save kayakers, avid fishermen, environmental enthusiasts, and a healthy bird population.
Yet without ALCOSAN’s outfall, life on the Three Rivers would be much different.
Beginning in 1959, the outfall at the Allegheny County Sanitary Authority (ALCOSAN) wastewater treatment plant has quietly carried out one essential mission: returning treated water to the Ohio River.
“This outfall represents our responsibility to the rivers that define Pittsburgh. It has done its job reliably and without fanfare, returning millions of gallons of clean water a day back into the river system.”
When ALCOSAN’s wastewater treatment plant opened in 1959, the original outfall served as the primary discharge point for treated water from municipalities across Allegheny County.
For decades, it operated continuously—through storms, system upgrades, and growing regional demand—returning treated, clean water back into the Ohio River each day.
But as always, with time comes the tides of change.
In ALCOSAN’s case, change in the 21st century was largely driven by aging infrastructure, evolving environmental regulations, and a renewed passion for Pittsburgh’s rivers.
“As needs and expectations evolve and our communities grow, we have to be proactive—planning ahead, investing wisely, and making sure we are shaping our future with resiliency.”
Engineered to meet the standards of its time, the original outfall served reliably for more than half a century—up to and including construction on the North End Plant Expansion.
That expansion included:
In 2021, a new river wall was complete—another major step forward.
On January 16, 2025, ALCOSAN and its iconic outfall entered a new era.
At exactly 3:08 p.m., with the words “Start Treating Flow North,” crews retired the original outfall—switching flow in a new direction through the disinfection tanks.
Then on September 4, 2025, capacity officially increased to 295 million gallons per day.
“As ALCOSAN celebrates its 80th year, let us not forget that progress here has never slowed, thanks to everyone that has shown up every day, moving the needle bit by bit towards these milestone moments.”
Today, tucked away at the northernmost end of ALCOSAN’s wastewater treatment plant, the outfall remains largely unseen from the riverbank.
But those who love our rivers—the ones who fish, boat, and care for these waters—know the importance of the work. It’s a testament to engineering and responsible river stewardship.
The volume and location may have changed, along with the times. But now there is a new piece of history—quietly flowing into the future of Pittsburgh’s Three Rivers.
Want to learn more about how ALCOSAN protects the rivers that define our region? Explore the Clean Water Plan and how infrastructure upgrades support a healthier future.
Explore the Clean Water Plan