What is a Cross-bore
A sewer main line is the primary pipeline in a sewage system. All branching pipes carrying sewage from different locations are connected to the main sewer line. The main sewer carries the sewage from these branches to the treatment plant. A sewer lateral is the underground pipe that connects a residence or business to a main sewer line. Using traditional methods pipeline installers have difficulty locating non metal sewer lines. As a result, lateral sewer lines go unlocated and unmarked prior to drilling. Which can potentially lead to cross-bores being created. Cross-bores is the unintentional drilling of a new pipeline through legacy pipelines using trenchless drilling technologies. Cross-bores compromise the integrity of underground infrastructure.
Dangers of Cross-bores
A cross-bore is not a danger on its own. But in time, sediment can build up and block the sewer line. This build up can contribute to even more damage to the pipeline.If a drain cleaner or wastewater crew is unaware of an intersecting gas line and attempts to drill through one of these blockages, they can cause severe, even deadly, explosions. Cross-bores first entered public awareness in 1976 when a sewer drain cleaner hit a cross-bored gas line. This caused an explosion that resulted in two deaths. Taking measures to prevent gas line cross-bores is crucial to minimize the risk of property damage, injury and even death. The Gas Technology Institute reported 18 major cross-bore incidents between 2002 and 2012.
Industry and policymakers face a dual challenge of preventing new cross-bores and locating latent cross-bores. The industry has made significant progress in educating the public. Homeowners, plumbers, and excavators must call the gas utility if they experience a sewer line blockage before trying to clear it themselves.
Legacy vs New Construction
A cross-bore safety program accounts for both legacy and new construction. The legacy program has two distinct components. The first focuses on inspecting sites for past trenchless installs to confirm the absence of cross bores. Sewer system depth, material type and installation type are risk factors used to prioritize inspections. The second component focuses on informing homeowners and business owners to call their utility company before attempting to remove any blockage. The public needs to understand the importance of Sewer Safety Inspection (SSI) prior to having their sewer pipes cleared.
The New Construction component refers to locating and mapping existing underground utility pipes to mitigate cross bore risk when installing new infrastructure. The pre-construction inspection is extremely important as it will provide documentation of pre-existing structural defects. Once mapped, the information is provided to construction engineers. The precise location of sewer laterals and other utility lines prior to installing new utility distribution lines prevents cross-bores. To verify that no cross-bores were created during the project a sewer video inspections occurs post-construction . The resulting video and data will provide powerful evidence against any potential future liability.
How video inspection can detect cross-bores
There is an average of two to three cross bores per mile of sewer line. Large communities can have anywhere from 1,000 to 6,000 miles of sewer lines. That means a large community can have the potential of 12,000 to 18,000 cross-bores in one system. A sewer crawler equipped with a camera can give a detailed view of the interior of a pipeline for both new construction and legacy cross bores.
Using a combination of CCTV inspection cameras and with highly accurate GPS data collection, inspection crews can quickly locate cross bores in any underground utility. Specialized sewer crawlers with a lateral launch camera system allow for a visual inspection of the entire sewer system. The lateral launch system is also used to physically mark the location of cross-bore lines. Many gas and electric utilities have started to use these camera systems prior to installation of new lines, as well as after installation to ensure that no cross-bore events occurred within the sewer system. Ultimately, there is no fool-proof way to prevent cross-bores. However, new advances in technology with lateral launch sewer cameras and ground penetrating radar have greatly reduced the number of cross-bores.