Coast Guard caused freak explosion. What has your service abondoned that might come back to haunt people?

The Coast Guard dumped batteries from buoys for years. They have spent millions diving and picking up those old batteries after realizing that dumping toxic batteries wasn't very responsible. Abondoned copper cables would never have been thought to be very hazardous though. Actually, they are extremely valuable if you can find one and legally sell it. I had friend who found an abondonded lighthouse cable, dug it up and sold it for scrap. I think he got $10k for it and that was many years ago.

Now that story is something else. The Army has left unexploded ordinance all over he world. I'm confident that those will be haunting folks for a long time to come.

Oh, I don't know...nukes maybe?

Oh lets see about my brushes with "History" You know all the Mines they left in Adak, AK when they left after WWII assuming no one would be coming back or the bombs they pushed into the Ocean. Damn if we didn't go back (Great Place to Watch Vladivostok from) for the Cold War. "Where did we put those Mines". Yeah I've walked thru and old Mine Field. Stepped on Old Anti-Personnel Spike. We had to constantly call EOD for the Bombs washed up on the Beach. Years later I got stationed in Bremerton, WA and surprise surprise it was an Ammo Depot during WWII and they just buried a lot of the stuff. Nothing like the kinds coming home from the Softball field "Hey Dad Call EOD there is a Bomb in the Softball Field".

I can only imagine someone finding all the stuff we buried or hid while I was in.