They are called gathering pipelines. They're pipelines that gather oil or natural gas from wells then connect to processing facilities or tanks miles away.
In Texas, Houston Public Media found there are over 6,000 miles of such gathering lines, up 33-percent in just the past three years according to Texas data. Other oil & gas states have seen big increases as well.
In years past, gathering lines didn't get a lot of attention from state or federal regulators. The lines were often in sparsely populated areas and were only inches in diameter. That's different from the big transmission pipelines that carry oil or natural gas across the country, which can be several feet in diameter and are strictly regulated.
Federal investigator Susan Fleming with the Government Accountability Office took a look at how gathering lines have been growing with the surge in oil and gas drilling. The GAO found that most gathering lines in rural areas were unregulated and had grown not just in number, but in diameter.
"Unregulated gathering pipelines are much larger in diameter. In Texas they told us it could be as large as 36 inches and higher pressure so more operating like a transmission line," Fleming told a U.S Senate committee last September.
Last year, one such big gathering line carrying natural gas exploded and burned outside Cuero in South Texas, melting portions of a roadway and power lines. In 2013, a rupture and fire in East Texas caused the evacuation of a dozen homes. In 2010, a construction crew hit a gathering line in a remote area of the Texas Panhandle, killing two of the workers. (Here's a list of pipeline accidents.)
Federal investigator Fleming testified that with so much more oil & gas production, gathering pipelines are increasingly in areas that are anything but remote.
"Businesses and homes are moving out to areas that were formally remote so I think un-regulated gathering pipelines could pose increased safety risks because more people could be impacted," Fleming testified.
Using a State of Texas on-line pipeline mapping tool, we found clusters of gathering lines in the Houston area. One cluster was in the booming suburb of Katy. Following the map, we found a gas well next to a Kroger supermarket parking lot and a hundred yards from homes. The well-site had a warning sign that said, "Danger, High Pressure Gas Line.”
Should the people shopping and living nearby be concerned? The pipeline industry says at least in Texas the answer is no.
"For a line like what you've described in the Katy area, there are already existing regulations," says Charles Yarbrough, a pipeline company executive who leads the safety committee at the Texas Pipeline Association.
Yarbrough says Texas imposed safety regulations on gathering lines in populated areas way back in 2006. Then in 2013, the Texas legislature passed a law for the rules to apply to rural areas as well.
"It's a man-made object....and any one of them can fail because humans built it. But you should feel pretty comfortable with all the checks and balances and regulations we have which are just increasing not decreasing," says Yarbrough.
But there's a caveat to those new rules to cover rural Texas: they haven't actually been implemented yet. The Texas Railroad Commission which regulates pipelines is still working on them and Yarbrough says he doesn't expect big changes.
However, federal regulators are also drafting new rules to apply nationwide to all gathering pipelines, pipelines that were once not much of a concern.