One of the most important issues in the underground construction industry is largely hidden from view, and that’s part of the problem.
A cross bore is when one utility intersects with another. In too many cases, cross bores are out of sight and out of mind, which can have serious consequences.
“It’s clearly a big issue for all of the stakeholders in the industry because of the potential for extreme damage or personal harm should a cross bore incident occur,” says Dave Wisniewski, vice president of Underground Solutions for Vermeer.
Those stakeholders include not just equipment operators and contractors, he says, but also equipment suppliers like Vermeer, industry associations, municipalities, workers like plumbers and drain cleaners, and property owners.
A cross bore can occur with any two utilities, but the biggest concern is with gas lines intersecting with sewer laterals or mains because of the potential danger that carries. If a line is hit, the discharged gas could enter a home or commercial building, creating a hazard.
The Cross Bore Safety Association (CBSA), a United States–based organization that is attempting to address aspects of cross bores to protect against loss of life, injury and property damage, says there are believed to be thousands of cross bores of gas lines in sewers.
Wisniewski says cross bores usually occur for two reasons. First, it’s hard to detect sewer laterals. The pipes tend to be nonmetallic, which makes them more difficult to find with locating systems. More often, they are made of clay or concrete, which can be hard to see in clay or soil.
Second, sewer laterals often lie in areas of land where underground utility maps may not exist. They are usually on private property and technically fall in the jurisdiction of the property owner, but it’s not realistic to expect the average homeowner to locate and record their position, Wisniewski says. Meanwhile, municipalities usually own the mainline sewer pipes, and in many cases are exempt from state requirements for One Call locating services. This can make for poor utility location record keeping.
“The biggest issue with cross bores may be the ambiguity,” Wisniewski says. “There is no one specific person or entity who clearly has the responsibility and, therefore, incidents happen.”
Many trenchless contractors take it upon themselves to check for cross bores and try to not create new ones. Wisniewski co-chairs a Distribution Contractors Association (DCA) committee studying cross bores and points to a DCA position paper as a good source for best practices to try to avoid these intersects. Examples for contractors include thoroughly investigating properties, including doing onsite interviews and reviewing plat maps and excavation permits; potholing to locate underground facilities; and using technology like camera inspections or ground-penetrating radar.
For new installations, Wisniewski would like to see advancements in identification devices to be placed alongside the utility pipe so locating equipment can more easily find them and identify the owner of the pipe.