Thurston County, WA Septic Rating
Septic suitability in Thurston County, WA
Very limited
USDA puts Thurston County, WA at "Very limited" for septic absorption fields, the dominant reading across 91.6% of the county's soil. That reading means a conventional system is a poor bet here - it's already USDA's strictest "very limited" bucket, not a partial constraint. The county spans 723 square miles, home to 302,912 people.
What this number does and doesn't tell you
Nothing about Thurston County, WA's SSURGO figure applies to a specific address - it's a county-wide average. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Thurston County: conventional vs. engineered cost
91.6% of Thurston County carrying a "Very limited" reading changes the realistic budget here. 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.
Where this sits nationally
Among the 3,058 rated counties on this site, Thurston County, WA ranks 1,088 most-constrained nationally, and 19 of 39 within Washington.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems