Clark County adopts amendments to on‑site sewage code to align with new state septic rules

The Clark County Board of Health on March 26 adopted Ordinance 20250312, amending Clark County Code 24.17 (on‑site sewage systems and regulation) to align local rules with updated Washington state on‑site septic regulations that take effect April 1, 2025.

The changes are intended to make county rules “consistent with or at least as stringent as the state code for septic rules,” Chuck Harmon, program manager for on‑site septic programs at Clark County Public Health, told the board during a public hearing. Harmon said the state has worked on the rule changes for five to six years and that counties must be consistent with the new state standards.

The updates address several areas of practical effect for property development and septic system management. They increase minimum lot‑area requirements for new development served by septic — by roughly 500 to 1,000 square feet depending on soil conditions — and explicitly require space for both a primary system and a future replacement drain field. County staff said the lot‑size standard varies by soil type and water supply: in poor soils or where private water supplies are used, required areas can be substantially larger; under an alternative sizing methodology the smallest lots could be about 12,500 square feet, and in the…