Sinkhole risk in Washington County, VA: Sinkhole country

Sinkhole country

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

On soluble rock: 62%
At or near the surface: 62%
Buried under cover: 0%

What to do about a house in Washington County

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

That works out to roughly 348 of Washington County's 561 square miles on soluble rock, 348 of them with the rock at or near the surface. With about 54,098 residents (96 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 611 map points about 1.0 miles apart, so a pocket smaller than that can be missed or overstated.

Counties around Washington County

The closest county with no soluble rock mapped is Ashe County, NC, about 33 miles southeast. 4 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Bristol city, VA 15 mi southwest · 89% at surface
Russell County, VA 15 mi northwest · 64% at surface
Johnson County, TN 21 mi south · 21% at surface
Smyth County, VA 24 mi east · 55% at surface
Sullivan County, TN 25 mi southwest · 92% at surface
Ashe County, NC 33 mi southeast · 0% at surface

Which formation it is

The largest mapped soluble unit here is the Elbrook Formation (dolostone (dolomite)), Cambrian in age, covering about 12% of the county. Next is the Beekmantown Group at 11%.

The county also lies over the Saltville, Virginia, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Virginia

Washington County ranks 18 of 133 in Virginia for soluble rock at the surface, and sits above 90% of US counties on that measure.