"County officials told Action 4 News that six people were working near the pipeline at the time of the explosion." - http://www.team4news.com/Global/story.asp?S=7878064
Sounds like an accident during repair work rather than anything else.
More likely a cable TV company was placing direct bury cable with a vibratory blade or even somebody with a backhoe doing adjacent work and crossed the pipeline Rights of way, nicking the line and lighting it off.
If it had been a major natural gas transmission line it could rip out of the ground like a giant water wiggle for about 100 feet and blowoff sounding like a freight train for about 30 minutes.
Once encountered a dozer operator who didn’t pay attention to the rights of way, nicked a 1600 psi line and it tore all the skin off his body, throwing up into a tree, while it blew off for 30 minutes.
The line described probably came from a local producer or secondary plant prior to liquid petroleum shipping to a transfer station.