I did this once, I attached a weapon that destoroyed everything within the are where the mines was and they all exploded. I gave the weapoin a damage of 2.. So the mines would hurt the units..
But sometimes mines survived at the edge.. I dunno if you can make them explode in another way though..
The mines are most likely an object, and you should be able to add a lifetime update module which will cause them to self destruct after a certain period of time. You just need to figure out how long it takes them to hit the ground, and set that as the min and max lifetimes.