What Nemaha County, KS's soil rates for a septic system
Very limited
99.5% of Nemaha County, KS'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 99.5% of the county. Nemaha County, KS is 717.427 square miles with a population of 10,062.
What Nemaha County's reading doesn't cover
Two lots a mile apart in Nemaha 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 Nemaha County will actually do.
What a system would cost here
With 99.5% of Nemaha 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.
Nemaha County's rank among Kansas counties
Nationally, Nemaha County, KS is the 27-most-constrained of 3,058 rated counties for septic soil. Within Kansas alone it ranks 2 of 105.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems