Island County, WA: the USDA septic-suitability picture

Very limited

Island County, WA: USDA's soil survey calls 97.6% of the county "Very limited" for a septic leach field. A standard gravity system routinely fails on ground like this; the same share of the county falls in USDA's worst absorption-field bucket outright. The county spans 208.698 square miles, home to 86,478 people.

What this number does and doesn't tell you

This is a countywide, area-weighted figure across every soil survey map unit in Island County, WA - never a reading for one specific parcel. Budget $750-$1,850 for a real perc test on any specific parcel - that's the only figure a permit application accepts.

Island County: conventional vs. engineered cost

97.6% of Island 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.

Island County's rank among Washington counties

Among the 3,058 rated counties on this site, Island County, WA ranks 300 most-constrained nationally, and 4 of 39 within Washington.

Further reading

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