Subsurface Utility Engineering:

A Confirmed Cost Savings

As underground utility installations increase nationwide—whether through rural fiber expansion, urban sprawl, or infrastructure improvement projects—the need to accurately identify their locations before construction begins is becoming essential. Unexpectedly encountering utility lines during construction can result in significant damages, customer outages, and safety concerns and disrupt project costs and schedules. Subsurface Utility Engineering (SUE) addresses these issues by following ASCE 38-22 standards and using advanced geophysical equipment, expedited data processing, and industry training that has evolved with the technologies to accurately locate and map underground utilities throughout all portions of the project lifecycle.

The demand for a return on investment grows greater as project funding comes from multiple sources and SUE has a proven track record of providing the desired return. Studies conducted by universities, transportation committees, and the FHWA have provided the public with ample amount of data showing the benefits of SUE on transportation projects of varying sizes and durations. Because of this many departments of transportation implement this process into their project life cycles to save cost on the projects through DOT funding and in an effort to save costs for rate payers when utility relocation is reduced. While DOT’s are some of the larger promoters of this process, SUE has found its way into multiple markets across the world from oil and gas, electric, and all aspects of transportation.

Pennsylvania Department of Transportation: evaluation of subsurface utility engineering for highway projects: Benefit-cost analysis (2012):
  • Examined 22 projects, considering direct and indirect costs, showcasing the wide range of benefits, including:
  • Savings of $11.39 for every $1.00 spent on SUE.
Louisiana Department of Transportation and Development: Cost and Time Benefits for Using Subsurface Utility Engineering in Louisiana (2021):
  • Examined the potential benefits of SUE services in Louisiana DOTD projects.
  • Savings of $2.73 for every $1.00 spent on SUE.
Pennsylvania State University: Pennsylvania Transportation Institute of the Pennsylvania State University (2007):
  • Studied 10 SUE projects located in PENN DOT Districts.
  • Savings of $22.21 was saved for every $1.00 spent on SUE.
University of Toronto: Ontario Sewer & Watermain Contractors Association (2005):
  • Examined the mapping of SUE on 9 large infrastructure piping projects in urban areas of Ontario.
  • Savings of $3.41 for each $1.00 spent on SUE.
Purdue University: Purdue University Department of Building Construction Management (2000):
  • Evaluated the quantifiable cost savings of SUE on 71 highway projects in three states
  • Savings of $4.62 for every $1.00 spent on SUE.

SUE Quality Levels

Quality Levels may be thought of as degrees of risk, or how much information is really needed to adequately design and construct a project. Engineering plans typically contain disclaimers as to the accuracy of the utility information. There are four recognized quality levels of underground utility information ranging from Quality Level (QL) D (the lowest level) to Quality Level A (the highest level).

Each of the four quality levels is described as follows:

  • Quality Level D. QL-D is the most basic level of information for utility locations. it comes solely from existing utility records or verbal recollections, both typically unreliable sources. It may provide an overall “feel” for the congestion of utilities but is often highly limited in terms of comprehensiveness and accuracy. QL-D is useful primarily for project and route selection activities.

  • Quality Level C. QL-C involves surveying visible utility facilities (e.g., manholes, valve boxes, etc.) and correlating this information with existing utility records (QL-D information). When using this information, it is not unusual to find that many underground utilities have been either omitted or erroneously plotted. Its usefulness, therefore, is primarily on rural projects where utilities are not prevalent or are not too expensive to repair or relocate.

  • Quality Level B. QL-B can be one of the more effective ways of creating an accurate utility map and help eliminate many horizontal conflicts in a design. It involves the application of appropriate surface geophysical methods to determine the existence and horizontal position of virtually all utilities within the project limits. This activity is called “designating”. The information obtained in this manner is surveyed to project control. It addresses problems caused by inaccurate utility records, abandoned or unrecorded facilities, and lost references. The proper selection and application of surface geophysical techniques for achieving QL-B data is critical. Information provided by QL-B can enable the accomplishment of preliminary engineering goals. Decisions regarding location of storm drainage systems, footers, foundations, and other design features can be made to successfully avoid conflicts with existing utilities. Slight adjustments in design can produce substantial cost savings by eliminating utility relocations.

  • Quality Level A. QL-A, also known as “locating”, is the highest level of accuracy presently available and involves the full use of the subsurface utility engineering services. It provides information for the precise plan and profile mapping of underground utilities through the nondestructive exposure of underground utilities, and provides the type, size, condition, material, and other characteristics of underground features. Typically, this involves some type of vacuum excavation.

While cost savings for projects is a critical item, risk mitigation is just as important on a project and SUE addresses this as well by eliminating risk by creating accurate deliverables developed by SUE professionals correctly utilizing each ASCE 38-22 Quality Level (A, B, C, D) and the judgements made by years of experience gained by understanding underground infrastructure for all utility types.

References

Federal Highway Administration
Louisiana Transportation Research Center
Repository & Open Science Access Portal

This article was written by:
Rhett Sloan, PLS (GA, LA, MS, ID, PA, KY, OH, NY, SD, ME)
SUE Department Manager/Associate, SAM
rhett.sloan@sam.biz
SAM (Surveying and Mapping, LLC)