For decades, the many live chemical munitions (mostly artillery and mortar shells) discovered in World War I battlefields in Belgium and northwestern France were moved to a storage site at Vimy, France. The storage area now contains some 16,000 shells. Some of the ammo was from unused piles of shells that had been stored in bunkers and just left behind when the war ended. Many of the individual battles during World War I saw over a million shells fired. The portion of those shells that did not explode ("duds") was often over ten percent. These shells simply buried themselves into the torn up ground, to be discovered years later by farmers plows, construction crews or tourists. Many of the shells simply worked their way back to the surface because of erosion or changes in the water table. These munitions have not aged well, and it was recently discovered that some were decaying to the point that the mustard or phosgene gas in them was leaking out. France is beginning to move the most dangerous shells in sealed and refrigerated trucks to plants where they can be safely be destroyed. While not as dangerous as nerve gas, mustard and phosgene can cause injury and death. No one wanted to pay the high cost of destroying the chemical munitions, but now, with the increasing number of leaks, final disposal is unavoidable.