Sinkhole risk in Smith County, TN: Sinkhole country

Sinkhole country

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

On soluble rock: 87%
At or near the surface: 87%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 273 of Smith County's 314 square miles on soluble rock, 273 of them with the rock at or near the surface. With about 20,783 residents (66 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 280 map points about 1.1 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 Smith County

The closest county with no soluble rock mapped is Morgan County, TN, about 73 miles east. 5 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Trousdale County, TN 15 mi northwest · 85% at surface
Jackson County, TN 16 mi east · 58% at surface
Macon County, TN 19 mi north · 24% at surface
DeKalb County, TN 21 mi south · 61% at surface
Wilson County, TN 21 mi southwest · 94% at surface
Putnam County, TN 26 mi east · 60% at surface

The rock underneath

The largest mapped soluble unit here is the Nashville Group; Bigby-Cannon Limestone and Hermitage Formation (calcarenite), Ordovician in age, covering about 40% of the county. Next is the Ordovician [units] including Richmond Group (which includes Mannie Shale, Fernvale Limestone, Sequatchie Formation, and Arnheim Formation), the Maysville Group (which includes Leipers Formation), the Eden Group (which includes Inman Formation), and at 37%.

Against the rest of Tennessee

Smith County ranks 17 of 95 in Tennessee for soluble rock at the surface, and sits above 96% of US counties on that measure.