The Cross Bore Safety Association (CBSA) and numerous participating organizations and individuals have combined efforts to assemble the most comprehensive collection of recommendations to date for reducing the risk of creating new cross bores and eliminating existing cross bores in the recently published Leading Practices for Cross Bore Risk Reduction. Stakeholder recommendations, which are included in detail, are intended to serve as a guide to utilities, installation contractors, inspection providers, public outreach, drain cleaners, public safety regulators and public utility rate makers.
Cross bores are an intersection of an existing underground utility by a second utility resulting in direct contact and damage. While trenchless installation methods offer numerous advantages, utilization of these methods must also ensure no cross bores are created in the interest of protecting the public, workforce safety and enterprise value of the companies involved.
Cross bores were first recognized at a federal level in a 1976 NTSB Safety Recommendation, which resulted from an incident in Wisconsin involving the injury of four persons and death of two persons from a natural gas line that was installed through a sewer lateral. Since then, and especially within the last decade, natural gas line cross bores traversing sewers have been the primary focus of cross bore prevention efforts; in large part, due to the potential for catastrophic results. The new Leading Practices estimates 300,000 cross bores have been or will be found in the U.S. and Canada, an average of approximately 0.4 cross bores of gas distribution lines intersecting sewers per mile. While the range of risk varies widely between gas service areas and the variability of sewer installations, with costs of a single incident reported as high as $30 million, the prompt location of existing cross bores and prevention of future cross bores is of immediate importance.
Opportunity for regulators to mitigate these risks includes recommendations that sewer utilities locate their infrastructure in the same manner as other utilities. Legal hurdles do exist, as lateral sewers are often not owned by the sewer utility, but instead by the structure owner who is unlikely to have the means to perform inspections. Potential solutions for legal elements are discussed. Other opportunities for regulators to improve cross bore risk reduction is to fund legacy cross bore removal programs with rapid rate recovery mechanisms. Legacy cross bores can be viewed as part of a construction program that should have been performed at the time of construction, even though long in the past, allowing construction-related cross bore inspections and associated costs to be, in essence, a part of capital programs.
For natural gas installations, Leading Practices recommends a combined approach including pre-construction location of existing sewers and a post-construction inspection to verify the sewer has not been intersected. Robotic and manual cameras are the most widely used tools for pre- and post-construction inspections and all processes are recommended to be verifiable and include QAQC to ensure high confidence results. Confidence in these verifications is increased by collecting GPS data points for viewing in GIS mapping software to ensure the correct area was inspected and the distance of inspection traverse was beyond the risk. Another recommended option is to pre-locate all sewers followed by daylight/vacuum excavation at each crossing. The viewing of the crossing would require a GPS location and photo or video of the crossing to meet the verifiable recommendation.
Public outreach is a cost-effective first step, informing occupants and drain cleaners of the risk of cross bores, thus allowing safer clearing of sewers. As part of this outreach, natural gas utilities should provide website information and onsite support for drain cleaners where trenchless construction was used.
The Leading Practices for Cross Bore Risk Reduction is free to those that are members of CBSA or a participating, referenced, governmental or educational organization.
THE FIRST-EVER Leading Practices for Cross Bore Safety Course, developed by the Cross Bore Safety Association, is scheduled for March 23, 2021 during the Global Excavation Safety Conference in Tampa, FL. Learn more and sign up for updates at GlobalExcavationSafetyConference.com.
Mark Bruce is President, Cross Bore Safety Association. Learn more at crossboresafety.org.