Since 2013, both King County and the City of Seattle have been subject to consent decrees with the Environmental Protection Agency and state ecology department over sewage discharge.

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Decades-old sewer infrastructure cost King County $118,500 in fines after the Washington Department of Ecology found 27 cases in which wastewater discharge exceeded pollutant limits, five instances of unpermitted overflows and other permit issues.

The violations, which occurred in 2016 and early 2017, come as King County is working to upgrade its wastewater system. Since 2013, both King County and the City of Seattle have been subject to consent decrees with the Environmental Protection Agency and state ecology department over sewage discharge, said Shawn McKone, of the ecology department.

In areas with older infrastructure, both King County and Seattle feature combined sewer systems, relics of a less-sanitary, bygone era.

“You’ll find this throughout the country in older cities. They originally constructed the sewer and stormwater systems together and treated it all together at once,” said Mark Isaacson, the director of King County’s wastewater treatment division.

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During heavy rain events, combined sewers were designed to overflow, sending a diluted mix of stormwater and untreated sewage into local bodies of water like Puget Sound. That’s no longer a desirable place for raw sewage, though, and the county now has several means of mitigating stormwater events.

In some areas, the county uses large underground vaults to hold wastewater. When the rain stops, the wastewater is moved to large treatment plants. The county also has four special wastewater plants designed to handle overflow from combined sewers.

Most of the recent violations resulted from dechlorination problems at one of the four special combined sewer treatment plants, McKone said.

“The majority of the violations had to do with having more chlorine in the water discharge than is allowed,” he said of the 27 instances. “Only four of them dealt with exceeding bacteria limits.”

In other words, the system was failing to remove chlorine from treated wastewater before pumping it away.

The county is working on several projects to improve its treatment of combined sewer overflows. King County is currently constructing a fifth wet-weather treatment plant in Georgetown, Isaacson said. Both Seattle and King County are building an enormous tunnel to hold sewage and stormwater, and to prevent spills into the ship canal.

Last year, the ecology department fined King County $361,000 for the catastrophic failure of the West Point Treatment Plant, which was overwhelmed by high tide and heavy rains.