The United States has over 2.5 million miles of pipelines—enough to circle the earth 100 times—crisscrossing the landscape, carrying a variety of products such as natural gas and oil. Additionally, there are over 800,000 miles of public sewers and 500,000 miles of private lateral sewers connecting private property to public sewer lines. Utilities and energy companies install much of this pipeline network underground.
The nation’s energy and water infrastructure exists in all 50 states, and the ubiquitous nature of pipelines means that any construction project that breaks ground risks damaging existing infrastructure.
Laying new pipelines and updating aging pipeline infrastructure by using trenchless excavation technologies have increased the potential for companies to accidentally and unknowingly puncture existing infrastructure while drilling to install new pipelines. The result is that a new pipeline is inserted through punctured infrastructure. This type of pipeline damage is known as a “cross-bore.”
Cross-bores first entered industry, policy and public awareness in 1976 when a sewer drain cleaner hit a cross-bored gas line, causing an explosion that resulted in two deaths. While this tragic incident brought awareness of cross-bores, many remain undetected underground for years.
Advances in camera technology allowed for internal pipeline inspections in the 1990s. This led to greater understanding of the frequency with which underground distribution lines—generally electric, gas and cable lines—were being drilled through sanitary sewers, storm sewers and other utilities.
It is important to note that the frequency of cross-bores remains largely unknown and likely varies in different areas of the country based on past operating practices, state and local laws, depths of lines and density of populations. However, while there is no widely agreed-upon estimate, an extrapolation of reported cross-bores of gas lines and sewers suggests there may be hundreds of thousands of existing cross-bores in the U.S., at an estimated average rate of 0.4 per mile of pipeline. These are often referred to as “latent cross-bores.”
What is a cross-bore?
Cross-bores, the unintentional drilling of a new pipeline through legacy pipelines using trenchless drilling technologies, compromise the integrity of underground infrastructure. Trenchless digging technologies dig laterally underground to install new pipelines without disturbing the surface, thereby preserving landscaping, roads and other above-ground features. One-Call legislation requires most utilities to mark the location of existing pipelines; however, some industries and certain types of underground facility owners are not required to participate in the program in some states.
Many cross-bores involve sewer laterals on private property, which are exempt from One-Call legislation in many states. These sewer lines are often not made of metal and are difficult for pipeline installers to locate using traditional methods. As a result, lateral sewer lines have not always been located and marked prior to drilling, which can potentially lead to cross-bores being created. Utilities have been making changes in their operating practices since the early 2000s as they have come to understand this phenomenon.
Attempts to clear sewer blockages caused by cross-bores can result in punctures to gas lines and lead to gas leaks into residences and businesses with the potential for explosions. The Gas Technology Institute reported 18 major cross-bore incidents between 2002 and 2012.
Industry and policymakers face the dual challenge of preventing new cross-bores and locating latent cross-bores. The industry has made significant progress in educating homeowners, plumbers, and excavators to call the gas utility if they experience a blockage in their sewer line before trying to clear the blockage with a cutting tool.
Current Policy Landscape
The industry has primarily addressed cross-bores by working to educate various stakeholders and mitigate the potential threat posed by latent cross-bores. However, state public utility commissions, along with state and federal policies on pipeline safety, accident prevention and mitigation, all touch on the issue of cross-bores.
State public utility commissions have ruled on cross-bore remediation and prevention in two types of cases: budget requests for cross-bore mitigation and accountability for cross-bore prevention.
utilities may face challenges in funding timely inspections of all legacy pipelines which were susceptible to the risk of a cross-bore. In California and Minnesota, state PUCs approved rate increases for utilities to inspect for and repair latent cross-bores. Many utilities have taken the initiative to inspect for cross-bores, regardless of rate recovery considerations.
Determining responsibility for locating existing pipelines offers another challenge to utilities in cross-bore prevention, particularly in the case of legacy infrastructure. Some states specify in their One-Call legislation how excavators should approach digging near difficult-to-locate pipelines and who is responsible for damage when it occurs. However, accountability for damage from trenchless digging is often unclear when the location of existing sewer lines is unknown. In Kentucky, the utilities commission ordered gas and sewer utilities to prevent cross-bores through locating and avoiding sewer pipes during gas line installations.
The specifics of each ruling can be found below:
- In California, the utility, Pacific Gas and Electric, filed for a rate increase with the California Public Utilities Commission (CPUC) to invest in a variety of improvements. One of these was a cross-bore remediation project. The CPUC approved the increase.
- The Minnesota Public Utilities Commission has ruled twice on matters related to cross-bores. The first ruling came in 2011, following a cross-bore-related home explosion in St Paul: In an attempt to clear a clogged sewer line, a plumber hit a gas pipeline that had been drilled through the sewer several years earlier. In the 2011 ruling, the PUC granted Xcel Energy a petition to use deferred accounting for costs incurred in the inspection and remediation of cross-bores. In 2015, the PUC ruled in favor of a cost rider for Xcel Energy to allow the utility to recover infrastructure costs, including cross-bore inspection and remediation.
- In 1999, the Kentucky Public Service Commission issued a ruling on cross-bores. In the case, a sewer utility complained that a gas distribution company was damaging their sewer infrastructure through trenchless digging, which resulted in cross-bores. The gas utility countered that sewer locations were not marked—and were not required to be marked under the law—which made it difficult to locate and avoid the sewer lines. The commission ruled that the gas utility must avoid sewers and that the sewer utility must locate and mark its sewers.
One-Call, or 811, Legislation broadly ensures pipeline safety during construction, excavation and trenchless pipeline installation. This legislation establishes requirements for both excavators and operators of underground infrastructure, along with structural and procedural requirements on the part of the state, to prevent damage to underground infrastructure by excavation and construction projects. However, the specific requirements and the level of enforcement of those laws can vary considerably from state to state.
In Virginia, the Underground Utility Damage Prevention Act provides prescriptive rules for gas utilities when using trenchless technology. Specifically, the law requires sewer companies to mark the location of sewer pipelines and requires the party installing new pipelines using trenchless technology to exercise reasonable care. This legislation has received acknowledgment as a best practice for preventing cross-bores involving sewer pipelines in this report.
However, many state One-Call laws do not specifically address the issues leading to cross-bores. Several states do not require sewer operators to participate in one-call programs. As a result, sewer operators are not required to mark the location of existing infrastructure prior to the start of excavation projects, which increases the likelihood of cross-bores.
California and New Jersey, for example, exempt non-pressurized storm drains and gravity sewers from their one-call legislation. Arizona, Connecticut, Iowa, Missouri and Wyoming all have exemptions for sewer laterals located on private property. In this case, the responsibility for the upkeep of sewer laterals falls on private property owners, many of whom do not have the expertise to properly locate and mark sewer locations prior to excavation or laying new pipelines.
The federal pipeline safety code requires natural gas utilities to implement a Distribution Integrity Management Program (DIMP). This is an all-encompassing plan that requires utilities to perform a formal risk evaluation of all applicable threats to the gas distribution system. Then they must implement actions and initiatives to effectively address these risks, which can vary in significant and likelihood from one operator to another. PHMSA has made it clear that operators must address the risk of cross-bores in their DIMP plans.
The Role of Industry
The current state regulatory and legislative landscape does not always provide comprehensive guidelines for cross-bore prevention and elimination. Often, when pipeline disasters occur, the gas industry bears the brunt of legal and financial responsibility as well as damage to their reputation. Therefore, the gas industry develops methodologies to minimize cross-bore risk and to eliminate legacy cross-bores. For example, several membership organizations working toward safe trenchless digging and cross-bore elimination practices include the Distribution Contractors Association and the Common Ground Alliance, while the Cross Bore Safety Association is in the process of developing a best practices document.