Septic System Installation in Eastern Washington and North Idaho: Permits, Design, Installers and Inspections

A new septic system starts with a permit from the health district, not with a backhoe. In Washington a soil and site evaluation and a stamped design come first, and only an approved installer may build it. In Idaho the health district evaluates the site, issues the permit and inspects, and a registered installer builds it.

Call (509) 463-4972 Email us a question

Last reviewed: October 26, 2026

The order of work for a new system

Check that the lot can take a system. Ask the health district before you buy, if possible.
Get a soil and site evaluation by a person the rules allow to do one.
Have the system designed, and submit the application, site plan and design to the health district.
Receive the permit, and hire an installer approved for your county.
The installer builds to the approved design, and the district inspects before anything is covered.
Submit the record drawing. The owner may then begin using the system.

Washington: soil and site evaluation

WAC 246-272A-0220 says only professional engineers, designers or local health officers may perform soil and site evaluations. Soil scientists may perform only the soil evaluation. The evaluator reports enough soil logs to cover the initial drain field and the reserve area, the groundwater conditions and the date observed, topography, drainage, and features such as wells, water lines, surface water, abandoned wells, bedrock, buildings, property lines, footing drains, cuts and banks, driveways and existing systems. Soil is classified into seven types, and type 7, with clay and massive or platy soils, is unsuitable.

The owner or the owner's agent prepares the soil log excavations, so the evaluator can look at the soil profile in place. WAC 246-272A-0220(3) says the pits must be dug to three feet below the expected bottom of the drain field. SRHD publishes test pit construction guidelines on its septic page.

Washington: design and permit

WAC 246-272A-0230 says a system must be designed by a professional engineer or an on-site designer, with one exception: at the health officer's discretion, a resident owner of a single home not within 200 feet of marine shoreline may design the system for that home. The design flow for a house is based on 120 gallons per bedroom per day, with a minimum of 240 gallons per day, and the health officer may require more. WAC 246-272A-0232 sets the minimum tank: at least two compartments and 1,000 gallons for up to four bedrooms, with 250 gallons added for each extra bedroom.

WAC 246-272A-0200 lists what the application must contain: ownership and parcel information, the water supply source, the soil and site evaluation, a dimensioned site plan showing the initial system and the reserve area, and a detailed design with cross sections and calculations. The health officer responds within 30 days and may issue a permit that expires no later than five years after issue. SRHD says its Liquid Waste program is funded primarily by application and permit fees, and publishes an application form and a water adequacy guide.

Washington: who may install

Under WAC 246-272A-0250, only installers may construct a system. The health officer may allow the resident owner of a single home to install it, except when the system is within 200 feet of marine water, within 100 feet of surface water, or permitted under the reduced-standard repair table. The installer must follow the approved design and keep it on site, make no changes without the designer's and the health officer's approval, use only approved tanks, be on site during excavation and construction, make the system watertight except for the drain field, cover only after the health officer approves, and backfill with 6 to 24 inches of cover while grading to keep surface water from collecting.

Installers need approval from the local health officer under WAC 246-272A-0340. SRHD permits installers every year after an application, fees and a test at SRHD, and publishes the list of permitted installers. The Northeast Tri County Health District certifies installers and posts a list. Neither district endorses the people on its list.

Washington: setbacks, inspection and records

Setbacks come from WAC 246-272A-0210, Table IV: for example 100 feet between a well and the drain field or its reserve area, 50 feet between a well and the tank, and 10 feet between a building foundation and the drain field. The health officer inspects before cover or allows the designer to do so. When work is finished the owner submits a record drawing, accurate to half a foot, showing every tank opening, buried pipes and cables, and the reserve area (WAC 246-272A-0265). The owner needs approval before starting to use a new system (WAC 246-272A-0270).

Idaho

Idaho DEQ says the Panhandle Health District, one of seven public health districts, conducts site evaluations, issues permits and inspects installations under a memorandum of understanding with DEQ. For an individual system, DEQ says the owner should have a site evaluation by the health district and an installer before buying property and applying for a permit. A permit is required, and the installation is inspected by the district. IDAPA 58.01.03 section 011 says no system may receive wastewater until the final installation inspection is done and as-built drawings are completed.

Idaho splits installers into two registration types. A basic installer permit covers standard individual systems. A complex installer permit is required for systems such as evapotranspiration, aerobic units, pressure distribution, sand mounds and intermittent sand filters. Applicants take an exam and, DEQ says, provide proof of a surety bond of $10,000 for basic or $30,000 for complex. The permits expire each year. A homeowner may build a standard basic system on their own property with no hired help.

Idaho DEQ also says enhanced treatment may be required by site features: shallow soil, coarse soils, shallow groundwater or the outcome of a nutrient-pathogen evaluation. DEQ lists conditions that can lead to that evaluation, including groundwater or fractured bedrock within 10 feet of the surface.

How to prepare

Ask the district what records exist for the parcel, and whether a prior permit is on file.
Find property lines, the well, water lines and surface water on a plan.
Decide on the house size and bedroom count, since they set the design flow and tank size.
Plan where soil log pits can be dug and keep equipment off the area that will be tested.
Ask each designer and installer for a written scope that says what is included, and who applies for the permit.
Protect the reserve area from the start.

What changes the price

This site does not quote prices. Soil, groundwater, slope, the system type the site requires, design, district fees, tank size and the distance of the lot from town all change a new system's cost. The pumping cost guide goes through each one.

Published fee information

District fees are public. The Northeast Tri County Health District's fee schedule, effective January 1, 2026, lists an on-site sewage permit for a single family residence or flow under 1,000 gallons per day at $688, and $852 for 1,000 to 2,000 gallons per day. It lists $103 for re-inspection of an installation, $226 for an additional site inspection and $257 for a wet season evaluation with three site visits. Spokane and Idaho fees are on their own fee lists, and this site has not stated them. Installer prices are set by each company.

Reasons to trust this page

Each Washington step cites a section of WAC 246-272A, and each Idaho step cites IDAPA 58.01.03 or the Idaho DEQ septic page.
District details come from SRHD and the Northeast Tri County Health District.
No designer, installer or price is recommended.
The Panhandle Health District permit page could not be opened from this site's research server on October 26, 2026, so Idaho district steps rely on Idaho DEQ and IDAPA.

Frequently Asked Questions

Who can design a septic system in Washington?

A professional engineer or an on-site sewage system designer, under WAC 246-272A-0230. At the health officer's discretion, a resident owner of a single home that is not within 200 feet of marine shoreline may design the system for that home. Soil and site evaluations are done only by engineers, designers or health officers.

Who is allowed to install a septic system?

In Washington only installers approved by the local health officer, with an exception for a resident owner of a single home if the health officer allows it and the site is not near marine or surface water. In Idaho a registered basic or complex installer builds it, though a homeowner may build a standard basic system without hired help.

How big does a new septic tank have to be?

Washington requires at least two compartments and a minimum liquid volume of 1,000 gallons for homes with up to four bedrooms, plus 250 gallons for each additional bedroom. Idaho sets a 1,000-gallon minimum for a tank serving a single dwelling unit. The designer sizes the tank and the drain field from the design flow and the soil.

Does the health district inspect a new septic system?

Yes. Washington's health officer visits during evaluation, construction or the final inspection and inspects before cover, or allows a separate designer to do so. Idaho DEQ says the installation is inspected by the public health district, and no system may receive wastewater until the final inspection is complete.

Can I check a lot for septic before buying it?

Idaho DEQ says an owner should have a site evaluation by the health district and an installer before buying property and applying for a permit. In Washington, only engineers, designers or health officers may do the soil and site evaluation. Ask the district what records exist for the parcel and what a lot needs.

Sources

Request a quote

Tell us the town, what you need and anything you know about the tank. Your details go to this site's inbox.