Twin Falls County, ID's soil, for a septic absorption field

Very limited

90.1% of Twin Falls County, ID's surveyed soil comes back "Very limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption 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. Twin Falls County covers 1,921.716 square miles and counts 96,509 residents.

This is a county figure, not a parcel figure

USDA's survey covers the whole of Twin Falls County, ID at once, not any single address. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Twin Falls County.

System cost, conventional vs. engineered

Given Twin Falls 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 Twin Falls County, ID compares

Nationally, Twin Falls County, ID is the 1,256-most-constrained of 3,058 rated counties for septic soil. Within Idaho alone it ranks 15 of 44.

Before you act on this

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