Ottawa County, KS's soil, for a septic absorption field
Very limited
78.4% of Ottawa 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. This is the reading that pushes a project toward an engineered system rather than a conventional one, and it covers 78.4% of Ottawa County's land. Ottawa County, KS is 720.73 square miles with a population of 5,853.
What Ottawa County's reading doesn't cover
Two lots a mile apart in Ottawa 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 Ottawa County will actually do.
What a system would cost here
With 78.4% of Ottawa 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.
Ottawa County's rank among Kansas counties
Nationally, Ottawa County, KS is the 2,120-most-constrained of 3,058 rated counties for septic soil. Within Kansas alone it ranks 62 of 105.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems