What Napa County, CA's soil rates for a septic system

Very limited

Soil across 90.7% of Napa County, CA rates "Very limited" in USDA's septic-absorption-field interpretation. That reading means a conventional system is a poor bet here - 90.7% of Napa County lands in the strictest "very limited" bucket USDA uses. Napa County, CA is 751.976 square miles with a population of 132,727.

What Napa County's reading doesn't cover

Two lots a mile apart in Napa 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 Napa County will actually do.

What a system would cost here

With 90.7% of Napa 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, Napa County, CA is the 1,193-most-constrained of 3,058 rated counties for septic soil. Within California alone it ranks 33 of 57.

Before you act on this

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