I've hit two gas lines with my tractor's box blade. The first one was in the middle of a lot, a building burned down so someone just dropped a sack of concrete onto the shut-off valve when they cleaned up. Fast forward twenty years or so, I'm grading the lot when I hit a chunk of concrete. The blade bounces over it and I hit it again the next pass. It breaks and I shear off the valve. I have a stream of gas shooting into the air right behind my diesel tractor so I cut it off and step off and away. I call the fire department, they come out and pound a tapered plug into the line and I drive off and never hear anything else about it. The gas company comes out and pulls the abandoned tap and I finish the job the next day. The next time I hit one it was an abandoned tap buried in a driveway. I felt a little tug and smelled just a little whiff of gas. I drive a ways away and walk back over to where I smelled the gas and had to get down on my hands and knees to see the little bit of dust being blown up from the crack in the valve. This time I called the gas company direct. They came out and pulled the tap, then they sent me a bill for close to $500 worth of gas! We went 'round and 'round for months, finally I got stuck with paying around $150 or so ( it's been a while). The moral to the story, call the fire department, let them get there and then leave! **** calling the gas company!