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

Very limited

Soil across 95% of Tripp County, SD rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 95% of it sits in USDA's most-constrained bucket. Tripp County covers 1,612.289 square miles and counts 5,717 residents.

This is a county figure, not a parcel figure

Nothing about Tripp County, SD's SSURGO figure applies to a specific address - it's a county-wide average. A site-specific perc test, usually $750-$1,850, is what a health department will actually require before permitting a lot in Tripp County.

System cost, conventional vs. engineered

Given Tripp 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.

Where this sits nationally

Nationally, Tripp County, SD is the 671-most-constrained of 3,058 rated counties for septic soil. Within South Dakota alone it ranks 9 of 66.

Further reading

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