Since the mid-1970s, the utility protection industry has advanced greatly through the development of technology, project planning practices and state and local legislation. More than a decade ago, in reaction to construction-related damages to existing utilities, facility and infrastructure owners joined politicians in implementing laws that required an excavator to have existing utilities marked, but also to restrict mechanized excavation within the marked areas.
This process took advantage of technology that became commonly accepted in the 1950s by facilitating marking based on an interpreted location of the actual utility. Led by the Common Ground Alliance, the One-Call industry worked to organize stakeholder utilities, gain support from the local and state legislation, and develop a simple, standard process that could be adopted across multiple geographies and utilities. Since that time, the One-Call industry has been very effective in lowering the number of impacts to existing infrastructure, while saving countless lives and minimizing idle work hours and impacts to the community.

The Subsurface Utility Engineering (SUE) industry developed as the next logical evolutionary phase to further reduce lost time and money caused by impacts to existing utilities within new project boundaries. Aimed at the design phase of the project life cycle, engineers and SUE technicians develop mapping to better avoid conflicts with utilities and support planning for the relocation or protection of utilities. Leaders from the engineering community joined together to develop ASCE 38-02, “Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data,” which defines a standard level of care for professionals to follow in the development of utility mapping on civil design projects. Four quality levels were defined, which build upon each other as follows:

The professional liability insurance industry responded by acknowledging the performance of SUE as an extension of professional engineering or survey activities. State and local governments quickly embraced SUE as engineers recognized the value of the enhanced information, and the consulting industry responded by making the services widely available.

Over time, both the One-Call and SUE industries developed a primary source of providers and resulting business models that created competitive pricing structures. In response to the unit price nature of the contracts typically awarded for One-Call service, providers began to excel at training entry-level technicians on the use of the equipment to “locate” the target utility. SUE providers focused on the professional liability of creating an accurate map and became well versed at mobilizing multiple geophysical technologies to minimize risk by confirming utility locations. This divergence in business models created an inherent line between providers.

In all states, the law dictates that the One-Call system is to be engaged prior to any excavation. But when should a facility owner or contractor rely solely on One-Call, and if not, which SUE Quality Level is best suited for their particular application? There are potential consequences for using too much or too little SUE. Employing only Quality Level D in a mature urban area could lead to construction delays, while exceeding the cost of construction by performing test holes at every potential location on a project will likely cause a client to wonder why a pipe wasn’t installed while the ground was open.

One-Call Only

The best opportunity to rely solely upon the One-Call system is when the existence of utilities is not probable or where the data indicates a low possibility of utility population. Indications could include a lower level of property density, absence of municipal water or sewer collection systems and aerial distribution for electric and telephone services. Other considerations should include:

• The availability of right of way to adjust the proposed features should a utility be encountered
• The level of risk to cost and schedule from discovering a utility relocation or design adjustment during construction

Often previous knowledge of the site conditions, combined with One-Call locating, can provide enough information, reducing the need for a Quality Level B utility sweep to identify undocumented utilities. The most common application of this method is in emergency situations where a planned approach cannot be accommodated, such as when a utility pole has been struck by a vehicle and power and other service has been lost.

Quality Level D

As many project life cycles do include a planning phase, often the first step in the SUE process is more of a discovery procedure to gain a general knowledge of the density of existing utilities within geographic boundaries. This effort focuses on obtaining as many records as possible that together will indicate the existence and position of utilities relative to other known features. While many books could be written on the difficulty and obstacles that routinely develop in obtaining and interpreting the records to draw conclusions as to utility locations and configurations on a project, this research is an important step that requires a documented approach, organization and professional engineering judgment. It is these obstacles and the accuracy of the records available that creates the need for professional judgment and the possibility of a wide variance of results.

The value to this level of information is that it allows a project manager and owner to understand the density or population of utilities within a specific area, which could be instrumental in developing a strategy to move a project forward or eliminate elements based upon risk or cost. When projects go to construction with only Quality Level D information, a large contingency factor should be incorporated into the cost and schedule to accommodate modifications to design and right-of-way needs.

Quality Level C

According to the American Society of Civil Engineers (ASCE), the Standard Level of Care indicates that the engineer should inform the project owner regarding utility quality levels and recommend a scope for utility investigations dependent on project needs, meaning that there is a level of judgement to be made by the professional engineer who is responsible for the design to determine if and when SUE should be applied.

According to the American Society of Civil Engineers (ASCE), the Standard Level of Care indicates that the engineer should inform the project owner regarding utility quality levels and recommend a scope for utility investigations dependent on project needs, meaning that there is a level of judgement to be made by the professional engineer who is responsible for the design to determine if and when SUE should be applied.

Known as the upgrade to Level D, it is just that — a building block that enhances the previous level. By adding the survey of the surface features to the mapping from the record drawings, the engineer is able to make more educated judgments on the configuration of the portions of the utility that cannot be seen. It also allows the engineer to draw conclusions from measurements of existing features relative to the evidence available on the map.

While this approach certainly provides an upgrade to the previous efforts, it still falls short in interpreting the actual physical location of the utility and therefore relies on the accuracy of the interpretation of the record drawing if available. This approach also does nothing to account for facilities that were not identified in the research effort.
Many projects move forward with a level of success using this approach. Like Level D, each should incorporate a level of contingency that allows for shifting of proposed project features or a schedule that will accommodate a utility relocation.

Quality Level B

Since magic X-Ray 3D goggles have not been invented yet, the Quality Level B process is helpful in reducing the level of judgment made by the engineer a great deal. This process is the first step in determining the approximate physical location of the facility. By using multiple technologies, steps and approaches, an experienced and knowledgeable SUE technician can interpret the physical location of a facility with a relatively high level of accuracy.

It’s critical that engineers understand the process used by a technician during data collection and its inherent benefits and limitations. This will allow the engineer to evaluate the value of the data collected whether via ground penetrating radar or an electromagnetic unit tracking a tracer wire installed over a plastic gas main. Each method will provide an alignment that could be mapped and moved forward in the design process, but ultimately one will be more representative of the utility alignment than the other.

The best application of this method is to map out the project limits in order to determine available open space for proposed features. In areas where interaction with the mapped utilities is inevitable, engineers can focus on the details of the level of data collected by the SUE technician. It’s important to note that the Quality Level B process does not provide a vertical component and therefore cannot be used solely to eliminate conflicts of utility crossings.
One-Call system to mark utilities does not meet the criteria for ASCE Quality Level B because there is no opportunity for multiple technologies or the interpretive process involving the engineer and the SUE technician.

Quality Level B is preferred by engineers for mapping of utilities throughout a project site because it meets the standard level of care and reduces the necessity for interpretation of record drawings or broad assumptions. This method is best used on projects within public right-of-way where multiple utilities and agencies can place facilities, or on closed sites where the complete history of the site’s subsurface content is unknown.

Quality Level A

Excavation using an air-based vacuum method provides for the highest level of information with the lowest amount of risk to the utility. For those who are expecting the recommendation that this method be used 100 percent of the time, consider that it is easy to go overboard in the application of performing test-holes. This method could easily be intermingled with any of the ASCE quality levels or the One-Call only application.

The standard application of Quality Level A at horizontal crossings following the Quality Level B effort is still the recommended approach for eliminating the most unknown utility location risk, at least until backhoe operators can wear the 3D X-Ray goggles. However, on smaller scope projects where the need for excavation is limited, test-holes could be utilized at any stage, including the One-Call only approach, to safely install limited features. In this case, the technology could be an opportunity to find where a utility isn’t located. The best use of this method is where you absolutely need to know where a utility is or isn’t.


In summary, One-Call and each quality level of SUE have their place in the design and construction cycle depending on a series of considerations, including the project life cycle, utility environment, known site history, risk tolerances, schedule and cost constraints, as well as type and requirements of construction.

The most important take-away is that the engineer, project owner and contractor all need to understand the method in which the utility information was collected, the risk involved with this information and the assumed responsibility resulting from using the specific information. When making decisions to save money on SUE during engineering, all parties need to know the risks that are elevated during construction and what that potential costs are.
Scott Riddle is vice president and Gary Frazho is quality control and production manager at KCI Technologies Inc.