Challenges of Natural Gas Distribution Cross-Bores in Unmarked Sewer

With an increase in trenchless methods being employed for the installation of natural gas lines in urban areas, unmarked sewer service laterals present a risk of accidental and unknowing crossbores with these distribution lines. While the physical damage to underground facilities is always unwanted, a cross-bored plastic pipe natural gas distribution line in a sewer lateral is vulnerable to sewer cleaning tools that may be used in the event of a backup, with potential explosive consequences. There exists good practices for operators of horizontal boring equipment; however, these assume that the existing underground structures otherwise are marked and/or located. State legislation mandates the marking and locating of underground infrastructure; however, the question of who assumes responsibility for marking and locating sewer service laterals is a contentious one. Sewer system owner/operators generally place the responsibility of locating and marking in the hands of unsuspecting property owners claiming that the laterals are on private property. In reality, property owners lack the expertise and equipment to mark and locate these service laterals. This paper describes the challenges with respect to natural gas cross-bores in unmarked sewer service laterals.

There has been an increase in the utilization of trenchless methods for the installation of polyethylene natural gas distribution lines in congested urban environments. Methods such as horizontal directional drilling (HDD) and pneumatic piercing tools are now commonplace with contractors engaged in natural gas installation projects. These are necessitated by the need to create minimal disruption to surface activities in urban settings. A major concern facing contractors today is the issue of locating and marking of sewer service laterals as illustrated in Figure 1. A typical One-Call tickets involves the marking of utilities in the area of proposed construction including, in most cases, telecommunications, water, wastewater, gas, cable, and electrical lines. The real issue are sewer service laterals, which are exempt from marking by most One-Call statutes. The thinking is that these are on “private” property and as such are not the responsibility of the sewer system owner/operator. Municipalities, government agencies, Plastics Pipes XIII Washington DC, 2nd – 5th October 2006 trailer park owners, and other owner/operators are often hesitant to mark the location of laterals due to added costs; however, the bottom line is public safety. Several municipalities are following the lead of the City of Mesa, Arizona, which provides marking of sewer service laterals in the public right-of-way. City personnel diligently research available records to try and identify current lateral locations. According to Burt Williams (1), City of Mesa Utility Construction Coordinator, “our City Attorney’s Office and the reduced number of claims could conceivably be one of the major beneficiaries”. Several Arizona municipalities have agreed to undertake pilot projects to evaluate the viability of providing locates. This paper examines the issue of unmarked sewer service laterals and the dangers of potential cross-bores involving natural gas distribution lines.