Analysis of cross-bores in unmarked sewer service laterals

With an increase in trenchless methods being used for the installation of natural gas lines in urban areas, unmarked sewer service laterals present a risk of accidental and unknown cross-bores with these distribution lines. Although the physical damage to underground facilities is always unwanted, a cross-bored plastic natural gas distribution pipeline in a sewer is vulnerable to mechanized sewer cleaning tools that may be used in the event of a backup, with potential explosive consequences. Mainline sewers and storm sewers are also at risk from cross-bores; however, the scope of this paper is sewer service laterals. Although good practices exist for operators of horizontal boring equipment, these assume that the existing underground structures 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 issue. 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 and presents data obtained from a survey of 43 contractors involved in the distribution contracting industry. The results further support the need for immediate action related to unmarked underground sewer service laterals.