Sinkhole risk in Franklin County, MA: 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: 15%
At or near the surface: 0%
Buried under cover: 15%

What to do about a house in Franklin County

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

That works out to roughly 104 of Franklin County's 699 square miles on soluble rock. With about 70,871 residents (101 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 603 map points about 1.1 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: why the 15% under cover still counts, and how these percentages are measured.

Counties around Franklin County

The nearest county rated sinkhole country is Union County, PA, about 256 miles southwest. 3 of the 6 closest counties land in the same band; the ground changes quickly around here.

Hampshire County, MA 17 mi south · 0% at surface
Windham County, VT 29 mi north · 0% at surface
Cheshire County, NH 29 mi northeast · 0% at surface
Hampden County, MA 31 mi south · 0% at surface
Berkshire County, MA 35 mi southwest · 0% at surface
Worcester County, MA 38 mi southeast · 0% at surface

The rock underneath

The largest mapped soluble unit here is the Waits River Formation (schist), Lower Devonian in age, covering about 12% of the county. Next is the Gile Mountain Formation at 3%.

Against the rest of Massachusetts

Franklin County ranks 6 of 14 in Massachusetts for soluble rock at the surface, and sits above 0% of US counties on that measure.