Septic soil in Wahkiakum County, WA, by the numbers

Very limited

Soil across 90.4% of Wahkiakum County, WA rates "Very limited" in USDA's septic-absorption-field interpretation. 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. Wahkiakum County covers 262.928 square miles and counts 4,800 residents.

This is a county figure, not a parcel figure

Two lots a mile apart in Wahkiakum County can carry different soil, even though they share one countywide rating. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Wahkiakum County.

System cost, conventional vs. engineered

Given Wahkiakum 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 Wahkiakum County, WA compares

Nationally, Wahkiakum County, WA is the 1,226-most-constrained of 3,058 rated counties for septic soil. Within Washington alone it ranks 24 of 39.

Before you act on this

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