Official sources checked August 31, 2026

Lewis County, Washington septic permits and requirements

Washington state/local framework

Washington Department of Health states that the local health officer has regulatory jurisdiction over onsite sewage systems with design flows from 0 through 3,499 gallons per day. Local health jurisdictions permit and manage those systems and may administer local codes that are more protective than the statewide minimums.

County Environmental Health issues septic permits

Lewis County states that its On-Site Sewage Program evaluates site conditions and test-pit soils, establishes permitting conditions, and issues septic-system permits. The program also reviews subdivisions, boundary-line adjustments, special-use permits, SEPA matters, and other development proposals involving onsite wastewater.

Current local code

Lewis County states that an updated Lewis County Code 8.40 for onsite sewage systems became effective August 26, 2025. Applicants should use the current county program materials and code rather than older archived septic guidance.

Permit required for work outside the septic tank

Lewis County’s published O&M FAQ states that work outside the septic tank requires a permit. That county guidance is especially relevant to drainfield and other external-system repair or alteration work.

Test pits and site conditions

The county septic program specifically evaluates site conditions and soil characteristics in test pits as part of the onsite permitting process. Lewis County publishes separate test-pit guidance and conventional-system construction standards for applicants and septic professionals.

Final construction inspection

Lewis County maintains a dedicated septic construction final-inspection line and directs applicants to request the final inspection through Environmental Health after installation.

Certified septic professionals and published fees

Lewis County publishes a list of certified designers, installers, and pumpers together with application materials and fee information. Its published Public Health fee schedule includes local installer and pumper certification fees; applicants should confirm the latest county schedule before filing because service fees can change.

Official sources

• Washington State Department of Health — Regulatory Jurisdiction
• Washington State Department of Health — OSS Management Roles
• Lewis County — Septic Program
• Lewis County — Septic O&M FAQs
• Lewis County — 2026 Public Health Fee Schedule

SepticScope summarizes public-agency information for planning purposes. The permitting agency's current instructions control if they differ from this guide.