By Dave Moritz, PLS
The nation’s aging utility infrastructure has caused some major incidents that have heightened the urgency to make our communities safer. The 2014 water main break near the UCLA campus in Los Angeles and the 2010 natural gas explosion in San Bruno, California, are just two of many examples around the country.
One initiative is the institution of pipeline replacement programs that strengthen the integrity of existing systems.
Complicated and Challenging Pipeline Designs
The top priority for these programs is in our more populated areas, where new pipeline routes need to be designed under congested streets and highways. This results in complicated and challenging pipeline design requirements, as many of our streets are dense with subsurface utilities including new, old, and abandoned facilities. Determining the location of these existing utilities is a critical component in finding available space in a given street to place a new pipeline.
Designing these new pipeline alignments requires a strategic approach that minimizes the discovery of unknown utilities during construction. If existing utilities are not mapped correctly, unknown utility “strikes” can cause costly delays during construction and are prime candidates for contractor change orders. A study has shown that for every $1 spent on a good utility mapping program, $4.62 is saved during construction. Hitting an unmapped line and rupturing it can cause inconvenience and cost to a community, as well as potential safety issues. For example, unwittingly hitting a fiber optic cable can wipe out communications to an entire area, or hitting a main gas pipe could take out households gas supply, as well as Business Gas supplies, halting business operations – causing more loss of money for the community.
To avoid these issues, highly accurate mapping of existing utilities is essential. This is accomplished through a combination of surveying and Subsurface Utility Engineering (SUE). The American Society of Civil Engineers has developed a ranking system for mapping utilities using Quality Levels (QL A-D). The ranking starts with QLD, which is based solely on utilities plotted from record drawings, with no other confirmation or field verification. QLC utilities are drawn from surface evidence located by surveyors. QLB utilities are those that are detected by non-intrusive geophysical technologies, such as Ground Penetrating Radar (GPR), electromagnetic detection, radio detection, video camera, and metal detection, to name a few. QLA utilizes potholing, which is the excavation of a small hole to expose and positively identify the utility.
Each of these methods and rankings are used when mapping a pipeline project. The information is assembled into a SUE drawing that clearly labels the type, source and QL of each mapped utility. The SUE drawing, together with the background survey files (aerial mapping, field survey data and right-of-way lines), is given to the engineering teams so that a clear picture of existing conditions can be utilized to design the pipeline’s horizontal and vertical alignment.
Close-knit coordination between survey and engineering teams is essential. SUE is an important communication tool that gives engineers a high level of confidence when developing their designs.
Implementing a successful SUE program enables facility owners, surveyors, engineers, and contractors to increase the safety of our aging infrastructure with minimal cost and inconvenience to the public. It avoids unforeseen underground discoveries that can be costly, cause project delays, and even be dangerous to the community.
Dave Moritz, PLS is a senior project manager and Psomas’ Principal in Charge of pipeline surveying and mapping.