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Vashon Treatment Plant
Find information and facts about the Vashon Treatment Plant located on Vashon Island and the Beulah Park Plat Wastewater Treatment System and drain field.
Where does your water go?
When water goes down your drain, it does not just disappear. It goes to a system that cleans it before it returns to the environment.
On Vashon Island, wastewater does not all go to the same place.
Most homes use septic systems, which clean wastewater close to home. Some homes and businesses send wastewater to the Vashon Treatment Plant. The Beulah Cove area uses a community septic system that is separate from the plant.
Each system helps protect local water and the environment.
Status update
June 2026
Visit us at the Vashon Strawberry Festival. We'll have giveaways and staff on hand to answer questions about local wastewater systems and what not to flush.
How do Vashon Island residents get their water, and where does it go? Read our newsletter to find out, and learn how you can help keep our water clean by properly maintaining your wastewater system, whether you use sewer pipes or a septic tank.
Which system are you on?
Not sure if you’re connected to sewer pipes or on septic tank? You can check by visiting this tool and typing in your address.
Need help finding septic tank inspection professionals? Visit the King County Department of Health On-site Sewage/Septic System Program webpage.
Service area map
How it works – treatment process
King County runs the Vashon Treatment Plant and the Beulah Park system. Water is cleaned in steps, then disinfected.
Vashon Treatment Plant
Water is cleaned in steps at the plant, then disinfected to remove germs.
Wastewater sent to the Vashon Treatment Plant is cleaned in steps. The plant removes solids, cleans the water, uses UV light to kill germs, and releases the treated water. We recycle some of the solids back into the process because they have helpful bacteria that help clean wastewater.
Step 1: Wastewater flows in
Step 2: Solids are removed
Step 3: Water is cleaned
Step 4: UV disinfection
Step 5: Clean water released
Beulah Cove Community Septic System
Water is cleaned in steps, then cleaned again as it moves through the soil. This system is NOT connected to the Vashon Treatment Plant.
Step 1: Wastewater enters septic tanks
Step 2: Sand filters clean the water
Step 3: UV disinfection
Step 4: Water moves to drain field
Step 5: Soil cleans the water
Don’t flush trash
Your toilet is not a trash can. King County removes tons of trash from the system each year. This costs more than $150,000 and can lead to clogs, damage, and higher costs for everyone.
If it didn’t come out of your body and it’s not toilet paper, don’t flush it.
Only flush:
- Toilet paper
- Human waste
Everything else can cause problems.
- Wipes (even “flushable”) can clog pipes
- Grease hardens and blocks pipes
- Chemicals can make it harder to clean water
What you flush matters — especially on Vashon Island, where smaller systems can be affected more quickly.
Trap your grease
- Scrape grease from pots and pans into the trash
- Keep fatty foods out of the garbage disposal
- Let grease cool and throw it away
On septic? Take extra care
Flushing trash can still get you into trouble. Your household pipes and septic tanks are only designed to handle toilet paper
FAQ
No. Wastewater is cleaned before it is released or returned to the ground. These systems are designed to protect groundwater and drinking water.
Odors can happen from time to time, especially during maintenance or certain weather conditions.
If you notice a strong or ongoing odor, report it: Call 206-263-1760 (24-hour line)
The system is checked and maintained regularly. If something goes wrong, crews respond quickly to fix the problem and protect public health.
If you notice a problem, such as a sewage backup or strong odor, report it right away:
Call 206-263-1760 (24-hour line)
For vacuum system issues, contact the Vashon Sewer District the problem and protect public health.
King County and the Vashon Sewer District share responsibility for the wastewater system on Vashon Island.
King County:
- Treats wastewater at the Vashon Treatment Plant
- Operates the Beulah Cove system
The Vashon Sewer District:
- Manages parts of the local collection system
- Maintains and responds to issues with the vacuum system
- Works directly with customers on service questions
The Sewer District helps move wastewater from your home, and King County cleans it.
King County sets rates for wastewater treatment. This covers the cost to clean wastewater at treatment plants, maintain equipment, and meet safety and environmental standards.
Your total bill may also include charges from your local provider, like the Vashon Sewer District, for collecting wastewater and providing local service. For questions about your bill, contact your service provider.
Sewer service usually includes collecting wastewater from your home and treating it safely before it is released or returned to the ground.
Not all areas on Vashon Island are served by sewer.
To find out if service is available, contact the Vashon Sewer District. They can explain your options, requirements, and next steps.
Learn more
- Get the facts on the Vashon’s operations.
- Learn how Vashon contributes to a sustainable future for the surrounding community and environment.
- Explore educational opportunities.