I guess considering the long military history of the Washington-Baltimore area, stories like this one shouldn't surprise me, but it's still a little unsettling to think how many times I've driven through the Harbor Tunnel and they just now find 11 World War II era bombs. And these things were as big as 4,000 pounds, meaning a 2-kilometer radius had to be cleared in case one went off when they were trying to be moved.
Every now and then similar bits of unexploded ordinance show up in the D.C. area (and that's not even thinking of the abandon mustard gas and other agents found in Spring Valley in Northwest), but still it's amazing that these sorts of things could just be lost and forgotten.
After I'd been living in D.C. for about two years, part of Fort Meade was converted into the Patuxent Research Refuge. I went to go hiking there with a friend, but when checking in at the ranger station we were given a map and stern warnings not to step off the road or to stray away from a limited group of open areas. The rest of the refuge was slowly being cleared of unexploded ordinance from its days as a training ground. It wasn't the most relaxing of hikes.