What Madison County, ID's soil rates for a septic system

Somewhat limited

50.4% of Madison County, ID's surveyed soil comes back "Somewhat limited" in USDA's own SSURGO data, the county's dominant condition for a septic absorption field. That's a middle reading: not the outright failure "very limited" soil produces, but not a clean pass either. Design changes often bridge the gap. Madison County covers 469.267 square miles and counts 55,549 residents.

This is a county figure, not a parcel figure

Nothing about Madison County, ID's SSURGO figure applies to a specific address - it's a county-wide average. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Madison County.

System cost, conventional vs. engineered

Given Madison 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.

Madison County's rank among Idaho counties

Nationally, Madison County, ID is the 2,944-most-constrained of 3,058 rated counties for septic soil. Within Idaho alone it ranks 44 of 44.

Before you act on this

How this rating is built, and its real limits · How a percolation test actually works