Septic soil in Williamsburg County, SC, by the numbers
Very limited
97.2% of Williamsburg County, SC'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 97.2% of Williamsburg County's land. Williamsburg County, SC is 934.166 square miles with a population of 29,865.
What Williamsburg County's reading doesn't cover
Two lots a mile apart in Williamsburg 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 Williamsburg County will actually do.
What a system would cost here
With 97.2% of Williamsburg 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.
How Williamsburg County, SC compares
Nationally, Williamsburg County, SC is the 353-most-constrained of 3,058 rated counties for septic soil. Within South Carolina alone it ranks 3 of 46.
Further reading
How this rating is built, and its real limits · Conventional vs. engineered septic systems