As many know, the cleanup of WW1 is still an ongoing process, with tons of munitions still being found or defused every year. The area that contained the main Western Front battlefields contains the Zone Rouge (Red Zone), and in some places is still off-limits because of the dangers there.

When the Germans invaded the area again in 1940, and then the subsequent allied push following the Normandy landings in 1944, did the armies ever go through the Somme, Ypres, Verdun, or any other major WW1 battlefield? Did it effect them in any way either because of the warped terrain, unexploded ordnance, or residual chemicals left by the gas shells?