Septic System Permit - Cowlitz County Health Department

This is a Septic System Permit issued by the Cowlitz County Health Department for residential on-site sewage system (OSS) installation at 2423 Silver Lake Road, Castle Rock, Washington. The permit was issued on April 21, 2026, to applicant Advanced Septic Consulting and is valid through April 21, 2031. The project involves installation of a new gravity flow septic system with Treatment Level E serving a 3-bedroom residence with an anticipated design flow of 360 gallons per day. The system includes a 1,050-gallon two-compartment septic tank manufactured by Sound Placement Services, a gravity-type reserve drainfield with 2,250 square feet of land area, and primary drainfield specifications of 180 feet total length, 3 feet width, 540 square feet area, with 6-16 inches depth and 40% reduction amount using Infiltrator Systems Quick4 Plus graveless chambers.

The permit establishes comprehensive installation and maintenance requirements including mandatory inspections of drainfield and components prior to covering, Department of Labor approval for electrical work, and compliance with Cowlitz County Code Chapter 15.42 and Washington Administrative Code 246-272A/C standards. Critical conditions require the installer to follow approved design specifications exactly, obtain OSS certification from the designer, contact the Environmental Health Unit at least 24 hours before inspections, submit final system sketches, and prohibit structure occupancy until final inspection approval. The permit specifies maximum trench width of 36 inches, minimum 10-foot setback from trees, observation ports at drain line ends, and adjustable weirs in distribution boxes. Additional documentation required for final approval includes Designer Record Drawing, OSS Certification Card, sewer lateral inspection, existing septic tank pump receipt, and installer decommissioning statement. Homeowner installations require successful completion of a competency test administered by the Department prior to construction commencement.