What Clark County, ID's soil rates for a septic system
Very limited
91.3% of Clark 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. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 91.3% of Clark County's land. Clark County, ID is 1,763.145 square miles with a population of 794.
What Clark County's reading doesn't cover
Two lots a mile apart in Clark 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 Clark County will actually do.
What a system would cost here
With 91.3% of Clark 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.
Where this sits nationally
Nationally, Clark County, ID is the 1,144-most-constrained of 3,058 rated counties for septic soil. Within Idaho alone it ranks 14 of 44.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems