I used to work for a company that was based in New Jersey on the grounds of an old WWI munitions plant. Even as of a few years ago, they would occasionally find unexploded shells when they dug for construction.
Unexpected expense occurred when the Land Man determined it had been once been owned by the US gov and was a WWI bombing range for Ft Camp Bowie during that period.
I delivered a lot of 85 gallon steel salvage drums to that site.