Septic soil in Lake County, SD, by the numbers

Very limited

93% of Lake 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. Practically, that rules out a simple gravity system for most of the county - 93% of it sits in USDA's most-constrained bucket. Lake County covers 562.905 square miles and counts 11,006 residents.

This is a county figure, not a parcel figure

Nothing about Lake 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 Lake County.

System cost, conventional vs. engineered

Given Lake 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, Lake County, SD is the 934-most-constrained of 3,058 rated counties for septic soil. Within South Dakota alone it ranks 13 of 66.

Further reading

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