Find the Stormpike Explosives Expert and kill him. Return to the Frostwolf Explosives Expert when the task is complete.
I know all about landmines. I'm the one that lays all the mines on the front lines here, after all.
If you want to diffuse the Stormpike mine fields, all you have to do is kill their explosives expert. That dwarven coward is no doubt hiding in the first tower on the Field of Strife. Take him out and those landmines won't come back after they've been disarmed.
If you do happen to kill him, come back here and let me know. No good deed should go unrewarded.