Marlboro County, SC's soil, for a septic absorption field

Very limited

Soil across 80.6% of Marlboro County, SC rates "Very limited" in USDA's septic-absorption-field interpretation. Practically, that rules out a simple gravity system for most of the county - 80.6% of it sits in USDA's most-constrained bucket. Marlboro County, SC is 479.874 square miles with a population of 25,498.

What Marlboro County's reading doesn't cover

USDA's survey covers the whole of Marlboro County, SC at once, not any single address. A local percolation test, typically $750-$1,850 (around $1,300 typical), is the only way to know what one lot in Marlboro County will actually do.

What a system would cost here

With 80.6% of Marlboro 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.

Marlboro County's rank among South Carolina counties

Nationally, Marlboro County, SC is the 2,013-most-constrained of 3,058 rated counties for septic soil. Within South Carolina alone it ranks 18 of 46.

Further reading

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