Septic suitability in Whatcom County, WA
Very limited
USDA puts Whatcom County, WA at "Very limited" for septic absorption fields, the dominant reading across 97.1% of the county's soil. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 97.1% of Whatcom County's land. The county spans 2,107.928 square miles, home to 234,954 people.
What this number does and doesn't tell you
Two lots a mile apart in Whatcom County can carry different soil, even though they share one countywide rating. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.
Whatcom County: conventional vs. engineered cost
97.1% of Whatcom 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.
How Whatcom County, WA compares
Among the 3,058 rated counties on this site, Whatcom County, WA ranks 365 most-constrained nationally, and 7 of 39 within Washington.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems