One of my first assignments at Colliers Engineering & Design was to do research into cross bores, as it relates to Subsurface Utility Engineering (SUE), for an article. New to the world of engineering, I decided to jump into finding articles and white papers about a dangerous intersection hidden under the surface.

The Threat Beneath the Surface

According to the American Gas Association, cross bores are the unintentional intersection of a utility underground, with the newer utility being installed through an existing pipeline. Most commonly, cross bores occur between natural gas pipelines and sewer lines.

Cross bores can be a danger for all types of contractors, homeowners and the communities surrounding them. According to the Cross Bore Safety Association, the most danger lies within utilities intersecting with gas pipelines, which typically have a smaller pipeline. Cross bores with gas utilities are also the most dangerous, with multiple investigations and reports of lost life.

How Does this Happen?

So, how does this even happen? To better understand the dangers of cross bores, I spoke with Tre Hayes, Senior Subsurface Utility Engineering (SUE) manager from Collier Engineering & Design’s Denver office. From his experience, cross bores are created during installation of a new utility.

With so many thousands of miles of utilities right beneath our feet, it is dangerous to just be drilling and installing a new utility without a full and thorough investigation of the existing lines. According to Hayes, some contractors will create cross bores with concerns of cost-savings or by not following their bore, or hole.

“Sometimes, the contractors working on installing these new utility lines don’t have the time or expertise in boring or installing. Even more unfortunately, some contractors are more concerned with the price they are getting paid per foot of installation, rather than caring about the other lines or community around them,” Hayes said. “They think getting the job done fast is better than doing it right. Ultimately, that can lead to the loss of life and oftentimes, loss of business.”

Hayes has seen the devastation of cross bores firsthand, working alongside damage investigations where intersections existed with sanitary and gas lines. When the plumber was called to help unclog sewer pipes, he accidentally destroyed the lines in the utility, that should not be there to begin with. Once the gas begins leaking through the pipes and creating low pressure, any simple spark can cause an explosion. One move of the power tool resulted in damaged houses and loss of life.

Despite their high danger levels, cross bores were not fully known or documented until the 1970’s where a DOT investigation in an explosion resulting in death identified a natural gas pipeline was intersecting a sanitary line. Since then, organizations such as the American Society of Civil Engineers (ASCE) and the Cross Bores Safety Association (CBSA) have been dedicated to getting jobs done right and safely for everyone involved.