Snohomish County, WA's soil, for a septic absorption field

Very limited

Soil across 93.4% of Snohomish County, WA rates "Very limited" in USDA's septic-absorption-field interpretation. That reading means a conventional system is a poor bet here - 93.4% of Snohomish County lands in the strictest "very limited" bucket USDA uses. Snohomish County covers 2,086.518 square miles and counts 864,113 residents.

This is a county figure, not a parcel figure

This is a countywide, area-weighted figure across every soil survey map unit in Snohomish County, WA - never a reading for one specific parcel. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Snohomish County.

System cost, conventional vs. engineered

Given Snohomish County's rating, plan for the engineered-system range rather than the conventional one. The engineered-system range, $10,000-$40,000 (mound or aerobic treatment), is the more realistic number to plan around, against $3,000-$8,000 for a conventional system on the rare lot that passes.

How Snohomish County, WA compares

Nationally, Snohomish County, WA is the 865-most-constrained of 3,058 rated counties for septic soil. Within Washington alone it ranks 14 of 39.

Further reading

How this rating is built, and its real limits · Conventional vs. engineered septic systems