Sinkhole risk in Richland County, SC: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 47%
At or near the surface: 47%
Buried under cover: 0%

What to do about a house in Richland County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 356 of Richland County's 757 square miles on soluble rock, 356 of them with the rock at or near the surface. With about 430,651 residents (569 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 517 map points about 1.2 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Richland County

The nearest county rated sinkhole country is Calhoun County, SC, about 25 miles south, close enough that the same rock may run under the county line. None of the 6 closest counties land in the same band, so Richland County stands out from its surroundings.

Lexington County, SC 23 mi southwest · 15% at surface
Calhoun County, SC 25 mi south · 62% at surface
Kershaw County, SC 28 mi northeast · 57% at surface
Fairfield County, SC 29 mi northwest · 0% at surface
Sumter County, SC 31 mi east · 77% at surface
Lee County, SC 38 mi east · 88% at surface

The rock underneath

The largest mapped soluble unit here is the Peedee Formation /Black Creek Group, undivided (clay or mud), Cretaceous in age, covering about 19% of the county. Next is the Duplin Formation at 18%.

Against the rest of South Carolina

Richland County ranks 18 of 46 in South Carolina for soluble rock at the surface, and sits above 86% of US counties on that measure.