The U.S. has nearly 3 million miles of pipelines— carrying a variety of products such as natural gas and oil. There are an additional 1.3 million miles of underground public sewers and private sewer lateral lines connecting private property to public sewer lines.
In 1976, a sewer drain cleaner hit a cross bored gas line causing an explosion that resulted in two deaths. While this tragic incident brought awareness to the existence of cross bores, many still remain undetected.
Today, advances in robotic camera technology allow for a greater understanding of the frequency of cross bores and Mason Private Locating (MPL) has centuries of combined experience in cross bore mitigation and helping their clients protect valuable infrastructure during digging. Jake Mason, President of MPL, answered a few of questions from the private locating side of the equation.
WHAT IS THE DIFFERENCE WHEN SOMEONE CALLS 811 AND THEN CALLS IN A PRIVATE LOCATOR TO MARK AND INSPECT THEIR GAS INFRASTRUCTURE?
811 only marks what belongs to the utility company itself. Lines that belong to the property owners, schools, hospitals, etc., are not marked by 811 technicians. There are some exceptions to this. Sanitary sewer laterals are generally not located, neither are storm laterals. Systems owned by the property are not located unless contracted through a private locating service. Finally, abandoned structures, empty conduits and non-metallic/ non-traceable lines (which are often located by measurement only) are seldom accounted for in the 811 locate process.
CROSS BORES SEEM TO BE ACKNOWLEDGED NOW MORE THAN EVER. IS THIS NEW OR ARE WE JUST UNDERSTANDING THAT THESE HAVE BEEN HAPPENING FOR A LONG TIME NOW? WHAT HAS CHANGED?
Agreed, there are a few different factors. The first is the increasing use of directional drilling as the preferred means of installation, especially as the equipment and techniques have improved over the years. A lot of the gas infrastructure was placed a very long time ago. Over the years, these lines have begun to age to a point where they need to be replaced and the government has put certain programs in place requiring utility owners to update their facilities.
Second, as cross bores have increased so have the number incidents, especially with gas systems, and those incidents can be very dangerous.
ARE THERE GAPS IN THE SYSTEM? WE ARE MOSTLY REFERRING TO NEW AND LEGACY GAS LINES. HOW IS EACH BEING AUDITED AND WHERE DOES A PRIVATE LOCATING COMPANY FIT INTO THIS PROCESS?
There are gaps in the system. Master metered systems such as found in apartment complexes, campus environments and industrial sites often lack the tracer wire systems that make location of the utility-owned systems possible. Private systems may lack records or documentation concerning their location. And most importantly, private property owners seldom belong to the One Call System, and therefore may not be aware that digging will occur around their systems.
For a private system, there is no audit process that we have seen either for new or legacy systems. There have been projects where private utility owners have contracted to have a comprehensive utility map developed for their sites with use of private utility locators and surveyors.
WHEN IS A CROSS BORE EVENT MOST LIKELY TO OCCUR? AND HOW CAN WE PREVENT THAT?
A cross bore event is most likely to occur when you have multiple perpendicular crossings to existing utilities. In our experience, this is primarily in residential areas were there is a sanitary sewer lateral, water service, or storm lateral that is not located by the municipality or facility owner. There are instances when a contractor will look in a manhole and see that the sewer main is 8 feet in depth for example. In order to avoid the laterals tying into the main, they will then plan to drill at a depth of 3-4 feet. The problem with this is that the sewer laterals are not always at the same depth as the main.
I strongly suggest the use of the following:
• Require accurate records of the location of the expected utility conflicts
• Use both One Call (811) and private locators to ensure that all utility conflicts are marked
• Hand dig and/or vacuum excavate all utility crossings to confirm utility identity, location, and elevation
• Use lateral-launch CCTV cameras to confirm before and after conditions of all sanitary sewer/ storm sewer crossing
WHO IS RESPONSIBLE WHEN A CROSS BORE DOES HAPPEN?
Legally, the burden falls to the excavator. Especially when it comes to sanitary sewer/storm sewer laterals, water services or privately-owned systems. The nightmare scenario, which has occurred in the past, is the directional drilled gas line that goes through a homeowner’s sanitary line. The sanitary line becomes clogged, is snaked either by the homeowner or a plumber, the gas line is damaged, gas leaks back into the home and an explosion occurs.
WHAT MAKES OIL AND GAS LINES MORE DANGEROUS THAN OTHER UTILITIES?
There is no good utility to hit. That being said, gas is especially dangerous. Unlike electric with breakers or communication lines that just cease to work, gas can migrate. If undetected and it migrates into a confined space like a basement or vault, then an explosive environment can be created – just waiting for a spark.
ROBOTIC CAMERAS SEEM TO BE THE GO-TO TECHNOLOGY IN FINDING CROSS BORES, BUT ARE THERE OTHER IMPORTANT TOOLS USED IN THE PROCESS?
Vacuum Excavation is a must to allow for safe means of positively confirming the depth and location of utility lines prior to crossing – which is applicable to all utility lines. Robotic cameras are used in non-pressurized lines such as sanitary and storm sewer lines; a good private locator uses both.
HOW DOES ACCURATELY MAPPED UTILITIES WITH GIS SYSTEMS PLAY A ROLE IN MAKING THESE LINES SAFER?
Knowing the location of utilities is key in any project. And knowing the exact location is always better than an approximate location.
Accurately mapped utilities helps designers engineer around conflicts in the first place, minimizing potential risks. In turn, excavators with accurate maps will know if all the utilities along their expected pathway have been identified and located.