Slowing the flow to keep local waterways clean

Most people don’t think about what happens to what they flush or the sewer systems it flows into, unless things back up and cause a problem. But for King County’s Wastewater Treatment Division (WTD) employees, part of their jobs is to think about everyone’s sewage.

In King County’s regional sewer system, everything that goes down the drains from homes and business ends up at a few regional treatment plants that clean all of our water.

However, in the oldest parts of our regional system, pipes were designed to carry a mix of rain and sewage on rainy days, said Erika Peterson, community relations lead.

During heavy rainfall common to western Washington, these “combined sewers” can be overwhelmed with large water flows. Rather than backing up into streets and private property, the combined sewer pipes were designed to overflow at specific points where they flow into the area’s waterways, Program Lead John Phillips said.

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King County manages 38 of these overflow points, called combined sewer overflows (CSOs) and the City of Seattle manages about 90. All of them are located within Seattle. During most of the year, the pipes run at normal capacity. King County CSOs overflow during large rain storms a few times per year, Phillips said.

When they overflow into the area’s waterways, it pollutes the water, which if people have contact with, can make them sick. Seattle-King County Health Department and King County advise people to stay out of the water for 48 hours after an overflow has occurred. WTD posts signs at each CSO point, and the public can access real time information on the web about whether a rainstorm has caused an overflow.

“King County has been investing in fixing combined sewer systems since the 1980s,” Peterson said. “We fixed the easiest ones first and now are working on fixing the harder ones.”

As part of the final step, King County signed a “consent decree” agreement with U.S. Department of Justice, the Environmental Protection Agency and Washington State Department of Ecology in 2013. Across the nation, organizations like King County were being reviewed to examine how organizations were protecting the waterways. The consent decree insures that the County will have the final 14 uncontrolled CSOs managed by 2030.

It’s not all up to King County. Individuals can also help manage CSOs and help keep them from overflowing.

“Be careful what you flush,” Peterson said. “Only flush what we call the four P’s – pee, poop, puke and paper.”

Peterson warns against flushing anything else, including wipes that say flushable on the package. These wipes can clog and tangle in the pipe systems causing a backup or overflow.

Oils, pesticides and pet waste can also cause problems for the sewer system, Phillips said. Allowing these substances to be washed into waterways causes health problems, such as E. coli from contact with animal feces. WTD urges the public to properly dispose of pet waste.

Another way individuals can help is by managing stormwater at home. Through a program called RainWise, King County and Seattle offer rebates to homeowners who live in eligible areas. Homeowners can receive a grant to have a cistern (or large barrel that collects rainwater from gutters) or rain garden (landscaping that turns an individual’s lawn into a garden that collects and soaks up water). In both cases, rainwater is not running into the sewers. RainWise is available in some neighborhoods where King County and the City of Seattle are working to reduce CSOs.

For more information on combined sewer systems and RainWise, visit WTD’s website.