Septic soil in Union County, SD, by the numbers

Very limited

73.6% of Union County, SD'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 73.6% of Union County's land. Union County, SD is 460.757 square miles with a population of 17,402.

What Union County's reading doesn't cover

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

What a system would cost here

With 73.6% of Union 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, Union County, SD is the 2,343-most-constrained of 3,058 rated counties for septic soil. Within South Dakota alone it ranks 54 of 66.

Before you act on this

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