Ada County, ID: the USDA septic-suitability picture

Very limited

Ada County, ID: USDA's soil survey calls 87.6% of the county "Very limited" for a septic leach field. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 87.6% of Ada County's land. For scale: 1,052.252 square miles and 535,799 people call Ada County home.

Before you rely on this for one lot

Ada County's rating is an average across the whole county, not a promise about any one lot inside it. The real answer for one lot is still a site-specific perc test, running about $750-$1,850 (typically near $1,300).

Budgeting for a system in Ada County, ID

Ada County's soil reading pushes the likely outcome toward an engineered system rather than a conventional one. 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 Ada County, ID compares

Among the 3,058 rated counties on this site, Ada County, ID ranks 1,496 most-constrained nationally, and 21 of 44 within Idaho.

Before you act on this

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