Septic suitability in San Juan County, WA
Very limited
San Juan County, WA's SSURGO dominant class comes back "Very limited", covering 98.7% of the county. That reading means a conventional system is a poor bet here - 98.7% of San Juan County lands in the strictest "very limited" bucket USDA uses. For scale: 173.916 square miles and 18,668 people call San Juan County home.
Before you rely on this for one lot
Two lots a mile apart in San Juan County can carry different soil, even though they share one countywide rating. The real answer for one lot is still a site-specific perc test, running about $750-$1,850 (typically near $1,300).
Budgeting for a system in San Juan County, WA
San Juan County's soil reading pushes the likely outcome toward an engineered system rather than a conventional one. Conventional systems run $3,000-$8,000 where they pass; where they don't, engineered alternatives (mound or aerobic treatment, whichever the health department requires) run $10,000-$40,000 - budget toward the higher figure until a perc test says otherwise.
San Juan County's rank among Washington counties
Among the 3,058 rated counties on this site, San Juan County, WA ranks 133 most-constrained nationally, and 1 of 39 within Washington.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems