While researching an upcoming article about the horizontal-directional-drilling industry, several contacts mentioned "crossbores" as a troublesome aspect of trenchless utility installation. Crossbores? Have to admit it was new term for me.
Now, I'm old enough that the Internet still has an absolute fascination for me. I remember when researching an article meant you had to put on your coat, get in your car, drive to the library and spend maybe an hour finding the right reference book. With the Internet, the same process might now take 45 seconds (or about two sips of coffee). As I investigated crossbores, I quickly discovered the Cross Bore Safety Association (CBSA) (https://crossboresafety.org)..... Interesting and sobering reading.
CBSA officially defines crossbore as "an intersection of an existing underground utility or underground structure by a second utility, resulting in direct contact between the transactions of the utilities that compromises the integrity of either utility or underground structure."
Simply stated, when a directional drilling contractor inadvertently places a gas line or an electrical cable through a sewer lateral, the consequences can be devastating. The crossbore sooner or later will cause the sewer to clog, and if the plumber isn't aware of the crossbore potential, he might think it's a 10-minute job with a powerful root cutter.
If the plumber hits an electrical line, let's hope he was smart enough to insulate himself against electrical shock. If he hits a gas line, he could take out the entire neighborhood, as gas from the rupture seeps into and around the house and is ignited perhaps as the water heater fires up.
For various reasons, "one-call" utility locations don't always pinpoint sewer laterals. A conscientious drill contractor, of course, if he suspects a lateral might be in the bore path, will do his best to identify it by potholing. But even the most conscientious efforts might fall short.
So if you're in the underground business, spread the word about crossbore dangers. Or if you're just a homeowner, and your sewer backs up after some underground work in your front yard, insist that the plumber first investigate the problem with a down-hole camera. The added cost for this service will be insignificant compared with what you stand to lose.