Sinkhole risk in Prince William County, VA: 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: 2%
At or near the surface: 2%
Buried under cover: 0%

The next step for one property

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

That works out to roughly 7 of Prince William County's 335 square miles on soluble rock, 7 of them with the rock at or near the surface. With about 497,003 residents (1,482 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 424 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 Prince William County

The nearest county rated sinkhole country is Clarke County, VA, about 40 miles northwest, close enough that the same rock may run under the county line. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Manassas city, VA 3 mi north · under 1% at surface
Manassas Park city, VA 5 mi northeast · 0% at surface
Fairfax County, VA 14 mi northeast · 2% at surface
Fairfax city, VA 14 mi northeast · 0% at surface
Fauquier County, VA 19 mi west · under 1% at surface
Stafford County, VA 19 mi south · 23% at surface

What Prince William County is built on

The largest mapped soluble unit here is the Newark Supergroup; Conglomerate, mixed clasts (conglomerate), Triassic in age, covering about 1% of the county. Next is the Newark Supergroup; Jurassic Conglomerate at under 1%.

Against the rest of Virginia

Prince William County ranks 74 of 133 in Virginia for soluble rock at the surface, and sits above 58% of US counties on that measure.