Search form

Donate Today


How Future Superstorms Could Overwhelm Today’s Wastewater Infrastructure

Raw sewage dumps aren’t as rare as we’d like to think. And intense rain events — which climate change will make more common — could make these spills more necessary without infrastructure upgrades.

March 10, 2017

One of the three boilers at King County’s West Point Wastewater Treatment Plant is back on line, heating water to the ideal temperature for the microorganisms that digest Seattle’s sewage. That’s an improvement since February, when an electrical outage followed by a mechanical failure caused massive flooding inside the plant.


“This was all underwater here,” said Christie True, the director of the King County Department of Natural Resources and Parks, as she gestures at the plant’s entire boiler room, which must be at least twenty feet tall. Saying it was “underwater” is putting a polite spin on things. It was “completely submerged,” Christie adds, and it “has to get rebuilt, put back together.”

The malfunction forced King County to dump millions of gallons of raw sewage into Puget Sound, which horrified Seattle residents.

But raw sewage dumps aren’t as rare as we’d like to think. Even when no disasters happen, cities with combined sewers for their stormwater and sewage have to dump untreated wastewater into rivers, lakes, and bays during heavy rainstorms.

That begs the question of whether or not the county’s infrastructure is prepared to handle the heavier rain that climate change could bring.

In Seattle, Portland, and dozens of other cities across the country, toilets, storm drains, and street runoff all drain into the same pipe — so the West Point Plant treats a mix of stormwater and sewage.

The day of the electrical outage, it was raining hard, so wastewater was rushing into the plant — 440 million gallons of it during just 24 hours. That’s the maximum amount the plant can handle.

“When we’re at that kind of flow rate, there’s very little time to get the equipment up and running again,” True says. “The operators were trying to control the flow, and they had 2100 alarms going off at that time, so it’s very intense.”

The West Point Treatment Plant is operating at half its usual capacity, treating about 250 million gallons of wastewater a day. Eilís O’Neill, KUOW/EarthFix.

The nine workers at the plant didn’t fix things in time, so they ended up having to dump 180 million gallons of untreated wastewater into Puget Sound.

Power outages happen. Machinery fails. And climate change is expected to bring heavier rainstorms to the Pacific Northwest.

“The heaviest rain events are going to get more intense in the second half of the century — so after 2050, maybe not till the 2070s, 2080s,” says Guillaume Mauger, a climate scientist at the University of Washington. “Where that becomes important for stormwater is that stormwater infrastructure is long-lived.”

Even in a normal year, King County dumps about 800 million gallons of raw sewage into its waterways.

That’s because, when it rains too much in too short a time, “pipes start to flow too full,” University of Washington professor Scott Meschke says, “and so they start to back up. And, in order to prevent that, you have the overflow. If you didn’t have the CSO, it would go into people’s basements, or out their toilets.”

Cities are trying to limit how much untreated wastewater they dump into waterways, but upgrading infrastructure is expensive. Just a few years ago, Portland taxpayers spent over a billion dollars on new sewage pipes. The “Big Pipe”  project means Portland can handle a lot more rain.

King County is also working on a big pipe, which will capture water along the ship canal and reduce wastewater overflows there. But that pipe won’t be enough, either. So, like Portland, the county’s also looking at ways to keep stormwater from entering the combined sewer system in the first place.

Take this curbside rain garden on Orca Street, in Seattle’s Georgetown neighborhood. The road here used to flood all the time — but, now, the curb is cut so that water from the street can flow into the garden, which is a tangle of native ferns and grasses and bushes.

“That’s a snowberry. There’s a holly. We planted the tall fescue at the bottom which is the grassy stuff there,” says John Phillips, with the King County Wastewater Treatment Division, as he shows off the garden. “The fescue covers up the bottom area so the soil stays kind of moist.”

What this rain garden does is “it actually takes the stormwater out of our combined system and manages it onsite,” Phillips explains, “so it actually infiltrates it into the ground, which means it’s not going to the treatment plant.”

The stormwater trickles down into the soil instead of into the county’s pipes.

Washington state's permits promote low-impact development and installing things like rain gardens to absorb runoff. This rain garden was built by a West Seattle community group in 2011. Katie Campbell, KCTS9/EarthFix.

“Long-term, we think that’s going to help with any changes in the climate,” Phillips says. Green stormwater infrastructure, he adds, is “a tool for building climate resiliency,” because, “if we’re absorbing more water, then we’ll have less water in the system.”

King County’s goal is to have all the rain gardens and bioswales and some additional infrastructure up and running by 2030.


A worker repairs the electrical system following a malfunction at the West Point Wastewater Treatment Plant.

Eilís O'Neill, KUOW