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OperationsWater Quality

When the Unexpected Unfolds: Protecting People After Wastewater Overflows

By February 13, 2017August 26th, 2020No Comments

When conversations in our region circle around to water quality, the trigger is usually bad news.  Puget Sound’s resident orca whales had a tough year because they couldn’t find enough salmon to eat.  Shellfish harvests and beaches close due to toxic algae in the water. Fingers point at polluted stormwater runoff, combined sewer overflows, leaking septic systems, and more.

At King County Wastewater Treatment Division (WTD), our mission focuses on being part of the solution. We pride ourselves on the hard work we do treating our region’s wastewater, recovering resources from the wastewater system, and planning for a sustainable, resilient future.

The last thing we want to happen is an unexpected spill into the waterways we are trying to protect.

Operating a large regional wastewater system in an area like the Central Puget Sound means that overflows are always a potential.  King County operates 3 regional treatment plants, 2 local treatment plants, 4 combined sewer overflow treatment plants, 47 pump stations, 26 regulator stations, almost 400 miles of pipe, and even a community septic system.


The County’s regional wastewater system has a lot of equipment and moving parts. If you have ever been stranded on the roadside by a sudden problem with your well-maintained car, you know that despite your best efforts, moving parts can fail.

Our region’s seasonally wild weather can turn an unexpected operational problem into a crisis.  In heavy rains, stormwater that gets into the sewer by design or by neglect can swell flows beyond system capacity. Power outages mean backup generators have to switch on smoothly and run for hours or even days. Big weather systems and equipment problems can converge into a perfect storm for parts of our regional treatment system.

When the unexpected impacts the wastewater system, WTD’s emergency response protocols and trained teams kick in to high gear to protect facilities, workers, and the public.  We are “all hands on deck” until the problem is solved.

The West Point Emergency Bypass Incident

West Point2

West Point Treatment Plant, Seattle

On February 9, 2017, heavy rains and high tides combined with an equipment failure at King County’s West Point Treatment Plant, and caused an overflow of stormwater and wastewater into Puget Sound. The double whammy flooded the plant when it was operating at maximal flow rate, about 440 million gallons per day. Plant managers switched into emergency bypass mode to protect the plant and our workers.

Bypassing the treatment plant means incoming flows are shunted straight to Puget Sound through an emergency bypass outfall (EBO). Plant managers diverted as much flow as possible to other County treatment facilities, but we can’t shut off all flows to West Point.

Operations crews performed heroics all day to get the facility back to the point where they could finally shut the bypass gate.  By late evening, flows were receiving primary treatment and disinfection before going out the deepwater outfall about 3/4 mile offshore. By then, the emergency bypass had continued for 19 hours, discharging about 260 million gallons of untreated flow that was made up of 85-90% stormwater and 10-15% wastewater.

Overflows can affect Puget Sounders who enjoy our waters all year long

People living in the Central Puget Sound area don’t sit in warm homes nursing hot drinks during the rainy season.  We grow webbed feet, bundle up, and keep paddle boarding, diving, swimming, boating, kayaking, and fishing. Winter means the best visibility for divers.  Calm, sunny January days make for chilly but serene kayaking trips.

posting-signsKing County knows that it is critical year round to let people know if a system problem has affected our waters.  Main Control operators notify health and regulatory agencies immediately.  WTD employees put warning signs where people access the water in the area of an overflow.  We post incidents on WTD’s Web site.


King County’s Environmental Lab tracks water quality after overflows

When a sewer overflow happens, King County’s Environmental Lab samples affected waters and tests for bacterial contamination. Some urban waterways have periodic positive tests for bacteria from pet and wildlife waste. Wastewater adds human bacteria and other pathogens to that mix. Test results for intestinal bacteria quickly map problem areas, and over time, tell us when the waterway is safe for people once again.

Trained scientists take samples of the waterway and handle them as strictly as forensics experts handle evidence.  They map the sampling location by GPS, transport samples to the laboratory, and register them before starting analysis.

If you have ever looked at bacteria under a microscope, you may puzzle over how we can count the number in a water sample.  They wiggle and swarm and appear to number in the bazillions.512px-bacteria_photomicrograph

One type of water quality testing takes advantage of something living bacteria do when they have enough food, space, and a comfy home:  multiply.  One bacterial cell divides into two, then two divide to make four, and so on.  Lab employees spread a water sample on a gelatin-like layer of growth medium in a dish, put the dish in an incubator that’s warmed to human body temperature and voila! About a day later, a single bacterium has created a colony that you can see by eye.


A lab technician counts colonies on plates treated with different dilutions of the original water sample. Math happens, using the colony number and dilution to calculate the number of bacteria in the water.  The result is described as colony-forming units (CFU) per 100 milliliters (ml).  For Americans who never outgrew the Imperial Unit system of measurement, 100 mls is a little less than half a cup of water.

Values at or above 200 CFU/100 mls confirm the need for ongoing beach closures.

Find online videos on bacterial movement and multiplication. The most entertaining (and unforgettable) are musical animations for classrooms. You’ll never ignore a warning sign again.

Lab results map discharge from the West Point incident

WP_AerialUnderstanding currents helps the Environmental Lab to determine the right sampling sites.  The EBO for West Point Treatment Plant extends off North Beach at Discovery Park.  When the tide is receding, currents travel roughly in the direction of Golden Gardens Park.  When it floods, the currents reverse. The point buffers the South Beach from North Beach currents.

slide1Each day for several days, Environmental Lab employees sampled waters at the beaches in Discovery Park, Golden Gardens Park, and Carkeek Park. Each day, they reported results.  The results tell a story.

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As expected, the bacteria counts were higher on the North Beach at West Point, where the EBO discharges.  The lower South Beach counts illustrate the mostly northward current direction and blocking effect of the point. Moving northward, low bacteria levels showed up at Golden Gardens Park, meaning the current didn’t carry the discharge that far.


Why did bacteria counts drop so much the next day at West Point?  It’s not just dilution by tide exchange and wave action. The simple truth is that the cold, salty marine environment is nothing like the warm, food-rich place in your intestines. Gut bacteria that find their way into Puget Sound don’t just stop multiplying: they die. As long as the source is cut off, bacteria levels drop. At West Point, when the EBO gate closed and disinfection resumed, live bacteria stopped flushing into the Sound.

Lab results help protect people

Warning signs stay posted at beaches and docks until Public Health- Seattle & King County reviews lab results and approves removal.  Washington State Department of Ecology establishes swimming beach water quality standards. WTD posts incident updates to give people choices about recreating in waters where an overflow occurred.

In our workplace, we use casual language to describe a very important goal: keep the poop in the pipes.  When nature or mechanics -or both- conspire to challenge that goal, King County WTD makes it a priority to protect public health by broadcasting warnings, monitoring, and reporting water quality problems.

Questions or concerns about the West Point Emergency Bypass?  Contact us at