Sully County, SD's soil, for a septic absorption field

Very limited

In Sully County, SD, 70.1% of the surveyed land carries a "Very limited" rating for a standard septic drain field. That reading means a conventional system is a poor bet here - 70.1% of Sully County lands in the strictest "very limited" bucket USDA uses. Sully County, SD is 1,006.727 square miles with a population of 1,468.

What Sully County's reading doesn't cover

Sully County's rating is an average across the whole county, not a promise about any one lot inside it. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Sully County will actually do.

What a system would cost here

With 70.1% of Sully 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.

Sully County's rank among South Dakota counties

Nationally, Sully County, SD is the 2,457-most-constrained of 3,058 rated counties for septic soil. Within South Dakota alone it ranks 59 of 66.

Before you act on this

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