At the 16th Annual GITA Pacific Northwest Conference at the Boeing Future of Flight Museum in Mukilteo WA, David Steiger gave a fascinating presentation about one of the major problems arising from our poor knowledge about the location of underground infrastructure. Cross bores are gas, power or telecom cables and pipes that bisect sewer pipes. Horizontal directional drilling (HDD), percussion moles and plows are trenchless techniques used to install natural gas distribution and other utility lines. These boring drill heads can easily go through sewer pipes without the driller being aware of it. Since the location of underground sewer pipes, either main line or laterals connecting the main pipes to houses, are only poorly known, cross bores are widespread. Hydromax USA specializes in detecting and mapping cross bores. In their experience in high risk, densely populated areas, as many as 3 cross bores per mile of natural gas distribution mainline have been found. The average is about 0.4 cross bores per mile.
Cross bores are dangerous. A typical scenario is that the cross bore leads to an obstruction in a sewer pipe. If this is a lateral, the house owner calls a plumber. The plumber bores out the lateral with a sewer cleaning machine that has a head that can cut through tree roots, the typical source of backed up sewers, and telecom or electric power cables or gas pipes with ease. The first documented case of a gas main being cut happened in 1976 and the resulting gas explosion killed two people and seriously injured four more. According to Hydromax the highest claim paid for a single cross bore incident was reported at $30,000,000.
Hydromax USA uses a robotic device that travels down sewer pipes including laterals and identifies and records the location of cross bores. Whenever they are found, the responsible utility rolls a truck a fixes them. Finding these problems is big business. Hydromax estimates that in the U.S. the total market for identifying and geolocating cross bores is about $1 billion per year.
Increased recognition of the injury, death and damage caused from cross bores has resulted in federal and state regulatory action. For example, the U.S. Department of Transportation’s 2011 Pipeline and Hazardous Materials Safety Administration’s (PHMSA) requirements of Distribution Integrity Management Program (DIMP) is intended to increase the integrity of gas distribution systems.
This problem is so prevalent that the Cross Bore Safety Association has been formed. The CBSA is a community of industry professional that have joined together to address all aspects of utility cross bores for protection against loss of life, injury and property damage.