Sinkhole risk in Lehigh County, PA: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 34%
At or near the surface: 29%
Buried under cover: 5%

What this means before you buy

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

That works out to roughly 118 of Lehigh County's 345 square miles on soluble rock, 101 of them with the rock at or near the surface. With about 385,655 residents (1,117 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 466 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: why the 5% under cover still counts, and the signs to look for and how an inspection works.

Counties around Lehigh County

The nearest county rated sinkhole country is Union County, PA, about 80 miles west. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Northampton County, PA 18 mi northeast · 33% at surface
Carbon County, PA 22 mi north · under 1% at surface
Berks County, PA 22 mi southwest · 22% at surface
Montgomery County, PA 30 mi southeast · 5% at surface
Bucks County, PA 32 mi southeast · 2% at surface
Schuylkill County, PA 33 mi west · 2% at surface

Which formation it is

The largest mapped soluble unit here is the Allentown Formation (dolostone (dolomite)), Cambrian in age, covering about 14% of the county. Next is the Beekmantown Group at 7%.

Against the rest of Pennsylvania

Lehigh County ranks 19 of 67 in Pennsylvania for soluble rock at the surface, and sits above 79% of US counties on that measure.