What Washington County, WI's soil rates for a septic system

Very limited

Soil across 83.7% of Washington County, WI rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 83.7% of it sits in USDA's most-constrained bucket. Washington County, WI is 430.644 square miles with a population of 138,727.

What Washington County's reading doesn't cover

This is a countywide, area-weighted figure across every soil survey map unit in Washington County, WI - never a reading for one specific parcel. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Washington County will actually do.

What a system would cost here

With 83.7% of Washington 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.

How Washington County, WI compares

Nationally, Washington County, WI is the 1,809-most-constrained of 3,058 rated counties for septic soil. Within Wisconsin alone it ranks 58 of 72.

Further reading

How this rating is built, and its real limits · Conventional vs. engineered septic systems