What’s causing Willamette River sewage spills?

2 of the sewage spills were caused by blocked sewer lines

A pipe opening into the Willamette River in downtown Portland (KOIN, file)
A pipe opening into the Willamette River in downtown Portland (KOIN, file)

PORTLAND, Ore. (KOIN) — For the second time in two weeks, sewage spilled into the Willamette River. A week ago the torrential rains caused the spillage, while the most recent one was caused by a blocked sewer line.

The city spent $1.4 billion on the 20-year Big Pipe projects completed in 2011, but those projects were never expected to completely stop sewer spills.

In 1994, the city and the Department of Environmental Quality could have decided to build an entirely separate stormwater system, but it would have been about double the cost of the Big Pipe — and ratepayers would have gotten much of the bill.

The Big Pipe is designed to eliminate 94% of the combined sewer and stormwater overflows, but they still happen every now and then.

The reason we negotiated something less than 100% is the people of Portland couldn’t afford to build the system that would be required to be 100%,” said William Ryan, the chief engineer for the Bureau of Environmental Services. “As high as our sewer rates are now, they’d be double to triple that very easily if we had built the system to contain all of the flows.”

The Big Pipe is doing what it was designed to do, and Ryan said it has to be looked at in context.

Before the Big Pipe there was 6 billion gallons of sewage going into the river every year over a combined 100 days.  Now, he said, the sewage overflows are rare.

The storm on Halloween dumped 190 million gallons into the river, he said, and called it a “100-year storm.”

Below is information from the Portland Bureau of Environmental Services:

Since the project was completed in 2011, there have been 13 combined sewer and stormwater overflows into the river, including 3 this calendar year.

One thing that may make the problem seem worse is that 2 other sewage spills were caused by blocked sewer lines.

As for what happened this past weekend, he said there “was a lot of mud and debris that flowed in the previous Sunday and it might have just worked its way down the system.”

When the sewage does go into the river, Ryan said “the river quality is already pretty well impacted by mud, debri and rain that is going in there.”

Other cities have combined systems like Portland, including Boston, Honolulu and Astoria.

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