Sinkhole risk in Allendale County, SC: Sinkhole country

Sinkhole country

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

On soluble rock: 100%
At or near the surface: 76%
Buried under cover: 24%

What to do about a house in Allendale County

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

That works out to roughly 408 of Allendale County's 408 square miles on soluble rock, 309 of them with the rock at or near the surface. With about 7,551 residents (19 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 475 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 24% under cover still counts, and the signs to look for and how an inspection works.

Counties around Allendale County

The closest county with no soluble rock mapped is Saluda County, SC, about 74 miles north. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Hampton County, SC 19 mi southeast · 70% at surface
Barnwell County, SC 20 mi north · 45% at surface
Screven County, GA 22 mi southwest · 5% at surface
Bamberg County, SC 24 mi northeast · 84% at surface
Burke County, GA 37 mi west · 3% at surface
Jenkins County, GA 38 mi west · 4% at surface

What Allendale County is built on

The largest mapped soluble unit here is the Huber/Lisbon/Barnwell Formations, undivided (sand), Eocene in age, covering about 51% of the county. Next is the Duplin Formation at 48%.

Against the rest of South Carolina

Allendale County ranks 8 of 46 in South Carolina for soluble rock at the surface, and sits above 94% of US counties on that measure.