Sinkhole risk in Lee County, SC: Sinkhole country

Sinkhole country

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

On soluble rock: 88%
At or near the surface: 88%
Buried under cover: 0%

What to do about a house in Lee County

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

That works out to roughly 360 of Lee County's 410 square miles on soluble rock, 360 of them with the rock at or near the surface. With about 15,958 residents (39 per square mile), much of the land is open, and the mapped rock may sit far from where people actually live. The figures come from 528 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: the signs to look for and how an inspection works, and how these percentages are measured.

Counties around Lee County

The closest county with no soluble rock mapped is Fairfield County, SC, about 53 miles west. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Sumter County, SC 18 mi southwest · 77% at surface
Darlington County, SC 20 mi northeast · 87% at surface
Kershaw County, SC 23 mi northwest · 57% at surface
Florence County, SC 32 mi east · 77% at surface
Chesterfield County, SC 33 mi north · 63% at surface
Clarendon County, SC 34 mi south · 79% at surface

Which formation it is

The largest mapped soluble unit here is the Peedee Formation /Black Creek Group, undivided (clay or mud), Cretaceous in age, covering about 39% of the county. Next is the Duplin Formation at 30%.

Against the rest of South Carolina

Lee County ranks 1 of 46 in South Carolina for soluble rock at the surface, and sits above 96% of US counties on that measure.