What Washington County, KS's soil rates for a septic system
Very limited
Soil across 93.5% of Washington County, KS rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 93.5% of it sits in USDA's most-constrained bucket. Washington County covers 894.759 square miles and counts 5,572 residents.
This is a county figure, not a parcel figure
USDA's survey covers the whole of Washington County, KS at once, not any single address. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Washington County.
System cost, conventional vs. engineered
Given Washington 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.
How Washington County, KS compares
Nationally, Washington County, KS is the 864-most-constrained of 3,058 rated counties for septic soil. Within Kansas alone it ranks 40 of 105.
Related guides
How this rating is built, and its real limits · Conventional vs. engineered septic systems