New septic system installation

A new septic system is part engineering and part paperwork. The design depends on your soil, lot size, slope, setbacks from wells and water, and the size of the home. In Thurston County, new systems and full replacements go through the county's permit process before installation starts.

How a new system comes together

1. Site and soil evaluation. A designer digs test holes to see how the soil drains and where groundwater sits.
2. System design. Based on the soil and the home, the designer picks a system type: conventional gravity, pressure distribution, mound, or an advanced treatment unit for difficult sites.
3. Permit. The design goes to the county for review and approval.
4. Installation. A licensed installer builds the system, with the required inspections along the way.
5. Final approval and records. The as-built drawing goes on record. Keep a copy, since it shows where everything is buried.

Types of systems you'll see around Olympia

• Conventional gravity: the simplest design, for sites with good soil and enough depth to groundwater.
• Pressure distribution: uses a pump to spread effluent evenly across the field, common where the soil is shallow or the field needs to be dosed.
• Mound systems: build the treatment area up above native soil when groundwater is high or soil is poor.
• Advanced treatment units: add a treatment step before the drain field for tight lots, shorelines, and sensitive areas. These usually come with ongoing monitoring requirements.

Planning ahead on raw land

If you're buying land to build on, the septic question comes first. Whether the ground perks, and what system it supports, affects what you can build and what it costs. Get a site evaluation before you close if you can.

Where we connect you with help

• Olympia
• Lacey
• Tumwater
• Yelm
• Tenino
• Rochester

Other septic services

• Septic tank pumping
• Septic inspections
• Septic repair
• Drain field repair & replacement