Unexploded ordinance is not just a west coast thing, apparently. In 2012, an unexploded 75 mm shell was found on the grounds of Worton Creek Marina. This is just across the Bay from Aberdeen Proving Ground. When our boat was there and they were testing, Stella would shake a little with every detonation.
https://baltimore.cbslocal.com/2012...llery-round-found-at-a-marina-in-chestertown/
One estimate says there are 100,000 unexploded mines worldwide:
Old sea mines still have plenty of spark
Love the final sentence: “Any ship can be a mine-sweeper—-once.”
As for old shells not detonating (from Wiki):
Although comparatively rare, unexploded ordnance from the American Civil War is still occasionally found and is still deadly 150 years later. Union and Confederate troops fired an estimated 1.5 million artillery shells and explosive cannonballs at each other from 1861 to 1865. As many as one in five did not explode.[36] In 1973, during the restoration of Weston Manor, an 18th-century plantation house in Hopewell, Virginia that was shelled by Union gunboats during the Civil War, a live cannonball was found embedded in the dining room ceiling. The ball was disarmed and is shown to visitors to the plantation. In 1999, a Civil War cannonball fell from a large tree in the yard of country music singer Jimmy Dean's home overlooking the James River, where it had been lodged since the battle of Chaffin's Bluff.[37]
In late March 2008, a 44-pound, 8-inch mortar shell was uncovered at the Petersburg National Battlefield, the site of a 292-day siege. The shell was taken to the city landfill where it was safely detonated by ordnance disposal experts.[36] Also in 2008, Civil War enthusiast Sam White was killed when a 9-inch, 75-pound naval cannonball he was attempting to disarm in the driveway of his home in a Richmond, Virginia suburb exploded. The explosion sent a chunk of shrapnel crashing into a house a quarter-mile away.[36]