You’re cleaning a clogged line from a home to the septic system in the backyard. As you are cutting through a tree root, you may be cutting into something much more dangerous. A normal, routine job can quickly turn into disaster if you happen to encounter a cross bore – a natural gas line or other underground utility accidentally installed through a sewer line.

It is impossible to know if you have a cross bore conflict without some footwork and research. If other underground utilities are anywhere near the sewer line, the potential is there due to the inaccuracies of horizontal directional installation methods and the inherent problems of accurately locating underground utilities.

Minnesota was the first state to enact guidelines for gas pipeline installers in May 2010. When issuing the guidance, the Minnesota Office of Pipeline Safety reported 155 known instances in the state in which gas lines were accidentally installed through privately owned sewer laterals. From 2000 to 2010, there were six incidents of gas lines being punctured by sewer cleaning contractors, three of which resulted in explosions, significant injuries and property damage.

There are many other documented cases across the nation. It has been a known hazard since at least 1976 when the National Transportation Safety Board cited a cross bore as the cause of a house explosion in Kenosha, Wis. Two people were killed, four hurt and two nearby homes were damaged. According to the NTSB report, “The destroyed house was not served by natural gas. However, natural gas, which was escaping at 58 psig pressure from a punctured 2-inch plastic main located 39 feet away, had entered the house through a 6-inch sewer lateral. The gas was ignited by an unknown source.”

While regulatory attention is increasing, the Cross Bore Safety Association (www.crossboresafety.org) says, “State regulations and ‘One Call’ type of services alone have not eliminated the problems of damage to underground utilities nor the risk of injury. It is an important step. CBSA believes that additional efforts are needed than are currently the standard of practice.”

Though states and other groups are taking actions to reduce the chance of cross bore installation incidents, there is still the risk of encountering an existing cross bore. The Virginia State Corporation Commission has issued safety guidelines for those working on sewer lines to go along with proper locating of underground utilities:

• Inquire with the owner, occupant or building maintenance people to determine:
  • The location of sewer facilities such as clean-outs
  • If there has been any recent excavation to install utility lines
• If the markings for existing underground utility lines cross the path of the sewer line, it may be a cross bore that is causing the blockage.
• Use a camera to identify the location of the blockage. If the evidence of recent excavation or the marking for a utility line is the same distance from the building as the blockage, again, there may well be a cross bore causing the blockage.
• If you reasonably suspect or determine the blockage is caused by a cross bore:
  • Do not attempt to clear the blockage with a mechanical device.
  • Get help from the utility operator that may be involved.
  • Hand dig in the area where the blockage and/or the cross bore may exist.

Of course, if a cross bore is discovered, work should be stopped and the local gas or electric utility notified. It may take some extra time, but that’s better than an explosion or electrocution.