Since the oil boom in western North Dakota began several years ago, the roads in this sparsely-populated corner of the state have been taking a beating. A typical shale oil well requires 2,300 truck trips in its lifetime, driven mostly over gravel roads. With nearly 6,800 wells currently operating in the Bakken oil field, that's a lot of heavy traffic. County road commissioners are struggling to keep up with all the maintenance, and dust has become a major nuisance. Now there's concern that the dust clouds could have negative health effects: in certain areas, the road dust contains a carcinogenic mineral called erionite.