Sinkhole risk in Sumter County, SC: Sinkhole country

Sinkhole country

Soluble rock at or near the surface across much of the county.

On soluble rock: 79%
At or near the surface: 77%
Buried under cover: 2%

What this means before you buy

Get a sinkhole or geotechnical inspection before buying, building or adding weight to a foundation.

That works out to roughly 524 of Sumter County's 665 square miles on soluble rock, 511 of them with the rock at or near the surface. With about 104,776 residents (158 per square mile), homes are spread across towns and farmland, and a mapped unit may or may not reach the developed parts. The figures come from 453 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Sumter County

The closest county with no soluble rock mapped is Fairfield County, SC, about 54 miles northwest. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Lee County, SC 18 mi northeast · 88% at surface
Clarendon County, SC 20 mi southeast · 79% at surface
Calhoun County, SC 28 mi southwest · 62% at surface
Richland County, SC 31 mi west · 47% at surface
Kershaw County, SC 32 mi north · 57% at surface
Darlington County, SC 37 mi northeast · 87% at surface

The rock underneath

The largest mapped soluble unit here is the Duplin Formation (sand), Pliocene in age, covering about 30% of the county. Next is the Bear Bluff Formation at 14%.

Against the rest of South Carolina

Sumter County ranks 7 of 46 in South Carolina for soluble rock at the surface, and sits above 94% of US counties on that measure.