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13930 WA-9, Arlington, WA 98223
Septic System Installation Cost in Snohomish County, WA
In Snohomish County, where Arlington is one of several places we serve, homeowners often ask me what a new septic system should cost and what a fair price looks like. I'm Art Nikolin, Operations Manager at Septic Solutions, and I'll break down what affects the installation price and explain the county program that may help cover part of the cost.
Quick Takeaways:
Quick Takeaways:
- The cost of installing a full septic system depends on soil conditions and system type
- Inspection and maintenance schedules depend on the system type. Conventional gravity systems should be inspected at least once every three years, while many alternative systems require annual or more frequent inspections
- Snohomish County's Savvy Septic program offers rebates for qualifying maintenance, plus grants and low-interest financing for eligible repair or replacement projects
- A permit from the local health department is required before any new system is installed
What a New Septic System Costs in Snohomish County
As of August 2026, our current Washington pricing is about $6,000 to $14,000 for a tank-only replacement when the existing drainfield can remain in service. A complete conventional system starts around $15,000, while alternative systems on difficult sites can reach $45,000 or more. The final cost depends on the approved design, soil and groundwater conditions, site access, setbacks, and how much of the existing system can remain in service.
What's Included in a Full Installation
A complete installation starts with site evaluation and system design by a licensed septic system designer or other qualified professional. The design and permit application are submitted to the Snohomish County Health Department for review before installation. Construction then includes excavation, tank and drainfield placement, required inspections, and final documentation.
Design, Site Inspection, and System Type
System type depends on the soil, groundwater, elevation, setbacks, available drainfield area, and other site conditions. A gravity system is generally less expensive when the approved design allows wastewater to move without pumps or other equipment. Other properties may require pressure distribution or another alternative design. The private designer's fee is separate from the installation price and varies by property and provider.
Snohomish County Permits and Financial Assistance
As of August 2026, the Snohomish County Health Department lists a $1,130 application-review fee for a new gravity or pressure-distribution system and $1,290 for other DOH-approved systems. A new OSS also carries a $385 installation permit fee. A licensed-designer submittal for a single-family repair costs $390, with the permit included. Replacement systems use the applicable new-system application fee. The exact fees depend on the approved system and scope. The Savvy Septic program provides financial assistance, including low-interest loans for repair or replacement, rebates for inspections and riser installation, and grants for qualifying low-income homeowners. The program is administered by the county in partnership with the Washington State Department of Ecology, Department of Health, and Craft3.
A Snohomish County Case: When a $5,056 Drainfield Repair Avoided Full Replacement
One of our documented North Marysville projects involved a septic system installed in 1988. The septic tank itself was still usable, but the drainfield had failed. During diagnosis, we found that filter fabric had been omitted during the original installation, allowing sand to migrate into the drain pipes over 38 years and compact the distribution lines.
The resulting drainfield work cost $5,056. Because the tank could remain in service, the project did not require a complete septic system replacement. This is why we do not estimate replacement cost from the age of the system alone. The condition of the tank, drainfield, and other components determines how much of the system actually needs to be replaced.
Read the full cost comparison and North Marysville case.
The resulting drainfield work cost $5,056. Because the tank could remain in service, the project did not require a complete septic system replacement. This is why we do not estimate replacement cost from the age of the system alone. The condition of the tank, drainfield, and other components determines how much of the system actually needs to be replaced.
Read the full cost comparison and North Marysville case.
Talk to a Local Crew First
Since we are based in Snohomish County, we work with septic systems throughout the area and can help you understand the installation or replacement process. Give us a call to discuss your property and the next steps toward getting a site-specific quote.
FAQ
As of August 2026, our current Washington pricing starts around $15,000 for a complete conventional system, while alternative systems on difficult sites can reach $45,000 or more. A tank-only replacement is about $6,000 to $14,000 when the existing drainfield can remain in service.
Pumping frequency depends on household use and what the inspection finds inside the tank. Snohomish County recommends having the tank inspected on the required schedule for your system type and pumping when sludge and scum levels show that it is needed.
Yes, through the Savvy Septic program, which includes low-interest loans, rebates for inspection and riser installation, and grants for qualifying low-income homeowners.
A permit from the local health department is required before any new installation, replacement, or major repair.
In some cases, yes. Our North Marysville case involved a 1988 system where the tank remained usable and the required drainfield repair cost $5,056, avoiding a complete system replacement.