What is a Cross Bore?
A cross bore is the intersection of an existing underground utility or underground structure by a second utility installed using trenchless technology. This results in an intersection of the utilities, compromising the integrity of either or both utility or underground structure.
Cross bores can occur between different types of underground utilities, including the intersection of a gas line or electric line and a sewer line or water line. These can be disruptive, costly and potentially very dangerous. Intersecting buried electric lines or gas lines can cause injury or even death. Intersecting buried communication cables can interrupt calls for emergency assistance.
How does a Cross Bore occur?
When a new utility line (gas, electric, telephone, or cable television) needs to be installed it is not uncommon for the utility providers to dig horizontally underground (called directional boring). Since this installation method does not involve digging a trench, it avoids damage to sidewalks, patios, landscaping, and existing utility lines marked after placing a one call notification to 811. Since there is no open trench and the boring can be 100 feet or more underground, it is possible to intersect another underground line.
Why can a Cross Bore be a problem?
In rare cases, a gas, electric or communications line may cross through a sewer pipe. If a plumber unknowingly strikes one of these lines while cutting through a sewer blockage, the line could be broken. In the case of a gas line, natural gas could enter the sewer system, possibly causing an explosion. In the case of an electric line, serious injury could occur to the operator of the equipment.
Suggestions to help prevent damage because of a Cross Bore
If you have a blockage or are scheduled to have your sewer or septic pipe cleaned, make sure the natural gas utility serving the area is contacted first (either by you or your sewer/septic cleaner) to determine if an in-line camera inspection is necessary.
Always assume that an obstruction involves a cross bore. Mechanical purging equipment (rooters) have the ability to damage underground utility lines. Collapsed sewer walls can also cause the rooter equipment to be misdirected outside of the sewer, bringing the equipment dangerously close to other buried utility lines.
Some information courtesy of Peoples Natural Gas and the Cross Bore Safety Association.
You can find out more about Cross Bores at www.peoples-gas.com/CrossBores.aspx and www.crossboresafety.org.