Multnomah County, OR's soil, for a septic absorption field

Very limited

74% of Multnomah County, OR's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. Expect the ground itself to work against a plain gravity system; USDA's strictest bucket alone covers 74% of the county. Multnomah County, OR is 431.012 square miles with a population of 795,897.

What Multnomah County's reading doesn't cover

Two lots a mile apart in Multnomah County can carry different soil, even though they share one countywide rating. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Multnomah County will actually do.

What a system would cost here

With 74% of Multnomah County rating "Very limited", a standard gravity system is not a safe assumption here. 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 Multnomah County, OR compares

Nationally, Multnomah County, OR is the 2,327-most-constrained of 3,058 rated counties for septic soil. Within Oregon alone it ranks 35 of 36.

Further reading

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