New septic system installation
Building on rural land or replacing a system that's done? Get connected with installers who work in Thurston County's permit process.
A new septic system gives a rural home or a full replacement its own wastewater treatment, designed for the soil and lot. In Thurston County, new systems and full replacements go through the county's permit process before installation starts. The outcome is a permitted system with an as-built drawing on record.
How does a new system come together?
- Site and soil evaluation. A designer digs test holes to see how the soil drains and where groundwater sits.
- System design. Based on the soil and the home, the designer picks a system type.
- Permit. The design goes to the county for review and approval.
- Installation. The installer builds the system, with required inspections along the way.
- Records. The as-built drawing goes on record. Keep a copy.
What types of systems are used around Olympia?
- Conventional gravity: the simplest design, for sites with good soil and enough depth to groundwater.
- Pressure distribution: a pump spreads effluent evenly across the field, common where soil is shallow.
- Mound systems: build the treatment area above native soil when groundwater is high or soil is poor.
- Advanced treatment units: add a treatment step for tight lots, shorelines and sensitive areas, usually with ongoing monitoring.
What affects the cost of a new system?
- System type. Gravity systems cost least; mounds and advanced treatment cost more to build and maintain.
- Soil and groundwater. These decide the system type.
- Lot layout. Setbacks from wells, water and property lines, plus slope and access.
- Design and permit fees. Paid before installation starts.
- Removing an old system. Replacements may include abandoning the old tank.
Prices come from the company doing the work, and a phone quote is only an estimate until someone has seen the system.
Buying raw 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
Common questions
How long does a new septic installation take?
It depends mostly on design and permit review. Once the permit is approved, installation itself often takes days rather than weeks, weather permitting.
What decides which system type I need?
Soil, depth to groundwater, lot size, slope and setbacks. The site evaluation answers this, and the county approves the final design.
Related services
More background: Thurston County septic guide.
Septic backing up or alarm going off?
Call now instead of sending a form. Backups are a same-day problem.