Sinkhole risk in Union County, SC: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 2%
At or near the surface: 2%
Buried under cover: 0%

What to do about a house in Union County

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 10 of Union County's 514 square miles on soluble rock, 10 of them with the rock at or near the surface. With about 26,678 residents (52 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 258 map points about 1.4 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Union County

The nearest county rated sinkhole country is Kershaw County, SC, about 63 miles east. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Cherokee County, SC 25 mi north · 5% at surface
Chester County, SC 26 mi east · 0% at surface
Laurens County, SC 26 mi southwest · 1% at surface
Spartanburg County, SC 27 mi northwest · 0% at surface
Newberry County, SC 28 mi south · 0% at surface
York County, SC 31 mi northeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Biotite gneiss with interlayered marble, calcsilicate gneiss, sillimanite-muscovite schist, and garnet-quartz rock (biotite gneiss), undetermined in age, covering about 2% of the county.

Against the rest of South Carolina

Union County ranks 30 of 46 in South Carolina for soluble rock at the surface, and sits above 57% of US counties on that measure.