The Importance of Pre & Post Cross Bore Inspection When Directional Drilling Occurs

The Importance of Pre & Post Cross Bore Inspection When Directional Drilling Occurs

How common are underground Cross Bores in the United States?

More common than you think.

According to the Cross Bore Safety Alliance’s estimations, there is at least one cross bore for every one mile of underground pipe in the U.S.

Not only are these inadvertent intersections of underground utilities common, they also are dangerous and sometimes life threatening. GPRS Senior Video Pipe Inspection (VPI) Project Manager, Andy Jurski, had his own encounter with this ongoing threat to underground infrastructure on a recent project in Northwest, Ohio.

One early Tuesday morning in September, GPRS was contacted by national wastewater management firm, Aqualis Company, to get a quote for a CCTV pipe inspection of a 50-inch storm water pipe for one of their commercial properties.

Scope Of Project:

Aqualis had contacted GPRS to inspect the storm sewer line to discover the cause of a sinkhole that had appeared aboveground in the back parking lot of the facility. This sinkhole posed a major health and safety risk to drivers and workers because it was located near the back loading dock where heavy semi-trucks come daily to deliver new supplies to the business.

This parking lot sink hole in Toledo, Ohio is marked off by cones to prevent further damage.

Goal of Inspection:

Aqualis needed to know the most likely cause of the sinkhole's appearance and a comprehensive, NASSCO-certified report of GRPS' findings. To accurately assess and map all details of the line, Senior GPRS VPI Project Manager, Andy Jurski, utilized an Envirosight Mainline Sewer Crawler equipped with WinCan Web software to ensure comprehensive video feedback of the sewer system.  Utilizing this equipment and software not only ensured that all aspects of the underground infrastructure were accounted for, but also that the lines were accurately mapped and marked to prevent any further damages from occurring if excavation was needed to repair the existing lines.

Key Findings:

During Jurski’s sewer locating inspection, he discovered three unknown lateral lines connected to the storm sewer line that were not on the original as built drawings provided to him. Andy inspected these previously unknown lines and accurately mapped them using an electromagnetic (EM) utility locator. He traced the frequencies given off by the sonde transmitter located on the head of his lateral launch sewer crawler to ensure traceability, and to provide accurate utility markings on the surface, with the depth of each line included. As Jurski completed inspection of one of the lateral lines, he came across an area of sediment build-up that inhibited the crawler from proceeding any further into the line.

Sediment Build-up in a Lateral Line.

Due to the sediment build-up almost completely filling the line, Jurski suspected a break in the storm line, or a joint offset that could have caused the blockage. If his suspicion proved correct, the foundation of the building could become compromised and sink into the ground due to the washing out of the dirt below. Not only can sinkholes be a result of underground sewer line damage; subsurface water main breaks can also be the cause in major sinkholes.

The results of a subsurface water main break can be catastrophic. For instance, a ruptured water main in the San Francisco Bay area on September 12, 2023 resulted in damage to local businesses and properties due to flooding. When the underground water main line broke, it washed out existing foundations to the road, causing a void which resulted in a major sink hole in the middle of a busy intersection. As reported by ABC 7 News Bay Area, local construction companies reported that the repair would take up to six weeks, while local residents believed it would be much longer than that before everything was operating normally again.

While sink holes can be caused by underground sewer line damage, water main breaks, and other subsurface damage, the majority of these events can be prevented with the right proactive care to existing infrastructure. When left unaddressed, these issues have major consequences.

To prevent ongoing damages like those detailed above, utilizing acoustic leak detection methods to pinpoint subsurface water leaks on pressurized metallic lines, pre & post cross bore inspections when directional drilling occurs, and bi-annual video pipe inspections to keep an accurate and up-to-date assessments and record of all underground storm and sewer systems (including laterals) are of the utmost importance. Industry-leading practices like these can result in the successful mitigation of sinkholes, large-scale water main breaks, fatal cross bore explosions, and other damages like water pollution and soil erosion, leading to collapsing foundations.

A Dangerous Encounter:

Back at the sinkhole in the Toledo parking lot, after the complete inspection of the first unknown lateral line, Jurski maneuvered his mainline crawler back into position to inspect the rest of the main storm line. After only a few feet, he discovered a second potential culprit behind the sinkhole. Here, the crawler showed Jurski a major threat to human life lurking in the subsurface: an electrical cross bore.

The threat posed by this second culprit was not the cross bore itself.  It was a threat because whomever had installed the existing electrical line knew they had cross bored through the storm sewer, and decided to cover it up with plywood in an attempt to prevent any further sinkhole collapses, instead of reporting the damage and fixing the issue.

One assumption that could be made about why the directional driller attempted to mask the problem is the fact that some storm sewer line repairs/replacements cost over $150,000, thus inhibiting profitability for the installer of the new utility. Why is a sewer line replacement so expensive? Because material, costs, man hours, equipment rental, and potential environmental fines are just a few of the factors that drive up the cost of the work.

Electrical line cross bored through existing storm sewer line & covered up with plywood.

After the discovery of the first cross bore on site, Jurski located and marked the exact location on the surface, so the site contact would know where remediations and repairs requiring excavation would be needed.

Cross bore marked accurately on the surface with green spray paint.

A Shocking Discovery:

After a brief pause to map and accurately mark the location of the electrical cross bore, Jurski proceeded with the rest of his sewer inspection. Using his mainline crawler, he encountered something he had never experienced on a jobsite before...

Only two feet away from his initial cross bore discovery was … another CROSS BORE!

Before you say “How it that possible?” think about this…

The estimate for cross bores left undetected in the U.S. is over one million, according to the Cross Bore Safety Association.

That means that there are at least another 999,998 cross bores estimated to be undetected.

In this instance, the utility had been installed and intersected the storm sewer line at the bottom of the pipe.  The orange glare shown on screen by the robotic crawler indicated that this cross bore was a telecommunication line.

Second cross bore on site, intersecting the storm line.

Jurski shared in his interview that he had never come across two cross bores on the same project, let alone on the same sewer line two feet away from each other.

GPRS’ Roving Reporter, Christian Wagenhauser interviews Senior VPI Project Manager Andy Jurski on the jobsite.

Jurski discussed the dangers presented to the public that can be caused by cross bores such as, sink holes, compromised underground infrastructure, utility outages (loss of power, electricity, water, gas, or telecom), sewer backups, injury, explosion, and in some cases death.

While these are not the only results that can be caused by cross bores, however, they are some of the most prevalent.

Post Inspection Review:

After the completion of the project and the accurate mapping of all utilities involved on site uploaded to GPRS’ infrastructure mapping & data storage platform, SiteMap®, it was officially determined that the as builts were incorrectly labeled and marked. The storm sewer and sanitary sewer were labeled improperly, and the three different lateral lines found on site were not on the original drawings. Jurski also shared his hypothesis for the cause of the sinkhole: The first cross bore found on site which consisted of the electric line drilled through the existing storm line. But this can only be confirmed with further inspection when repairs are made to the damaged lines.

Aqaulis Project Manager, Daniel Reis, shared how helpful the information GPRS provided was to the project.

Andy was really helpful and clear what needed to be done… I like not having to guess.

Recommendations for all Water & Wastewater Personnel:

After the completion of this project, it was clear that the underground infrastructure mapped on site had been inaccurately reported on the as builts, causing confusion. Inaccurate as builts plague construction projects around the world because they cause delays, budget overruns, safety issues, and costly redesigns. While everyone may want to have accurate maps, the overhead cost of equipment and expert personal to inspect and accurately locate all underground sewer and other utility lines is prohibitive.  

While generally every facility and municipal manager each has 3-4 different GIS systems that they use just to give a rough estimate of where their underground utility lines are, the true integrity of those lines and what is happening beneath the surface is left unknown without bi-annual sewer inspections occurring on all properties. When a comprehensive sewer or video pipe inspection occurs, it can show information that was not previously known, revealing dangerous utility intersections (cross bores), such as on this project.

Another key takeaway is that cross bores are much more prevalent than anyone would like to admit. The two found on this project were in the same line less than two feet away from each other and posed significant health risks if damaged.

It is recommended for all GPRS commercial, industrial, and municipal customers to mandate pre & post cross bore inspections when directional drilling occurs and bi-annual sewer inspections on all sewer systems, so that situations like this can be mitigated and/or avoided. Maintaining the integrity and health of our underground infrastructure plays a big part in ensuring everyone on jobsites and in communities remain safe.

To learn more about how you can protect your property through a pre and post cross bore inspection when directional drilling occurs and bi-annual sewer line and sewer lateral inspections with GPRS, sign up for a complimentary Water & Sewer Damage Awareness Week talk with a GPRS Safety expert, today!