That is really sad.  I didn't realize they could be so lethal close to 150 years after first use. 

Bombs are often found in Europe when new construction goes up.  There is a specially trained EOD unit of the fire department in most German and English cities that were heavily bombed in WWII.  I also remember reading a story about a farmer in France near the Somme who suffered Mustard Gas burns after cutting down a tree on his farm and sitting on the stump about ten years ago.  there is no reason why ordnance should not remain viable after sitting in the ground for many years unless the casing is ruptured.  Remember, artillery and bombs are designed to withstand terrific forces and only detonate when their fuses go off.  What is amazing to me is that more idiots don't kill themselves playing with Unexploded Ordnance.  While the stuff is tough it is not indestructible.  There was a guy in Houston who blew himself up two years ago after playing with a grenade he found that his dad had brought back from WWII.