Sinkhole risk in Gloucester County, NJ: 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: 9%
At or near the surface: 9%
Buried under cover: 0%

What this means before you buy

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

That works out to roughly 28 of Gloucester County's 322 square miles on soluble rock, 28 of them with the rock at or near the surface. With about 311,783 residents (968 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 442 map points about 0.9 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Gloucester County

The nearest county rated sinkhole country is Union County, PA, about 132 miles northwest. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

Camden County, NJ 11 mi northeast · 6% at surface
Salem County, NJ 15 mi southwest · 15% at surface
Delaware County, PA 19 mi northwest · 0% at surface
Philadelphia County, PA 20 mi north · 0% at surface
Cumberland County, NJ 27 mi south · 0% at surface
Burlington County, NJ 28 mi northeast · 4% at surface

Which formation it is

The largest mapped soluble unit here is the Mt. Laurel Formation (sand), Upper Cretaceous, upper Campanian in age, covering about 9% of the county.

Against the rest of New Jersey

Gloucester County ranks 4 of 21 in New Jersey for soluble rock at the surface, and sits above 67% of US counties on that measure.