In 1998, the Federal Highway Administration (FHWA) made it clear to the National Transportation Safety Board (NTSB) that Subsurface Utility Engineering should be used during the development of highway projects and one-call notification centers and/or utility companies should be notified to mark the ground indicating the location of the underground utilities prior to any excavation. This is a concept we firmly believe in – Subsurface Utility Engineering is for design, as one-call/utility notification and markings (locating) are for construction.

The following explains the difference, including when it is appropriate to use which process, between Subsurface Utility Engineering and locating.

Q. What is locating?
A. Locating determines the approximate horizontal location of an underground utility line that may exist within a pre-specified area.

Q. What is Subsurface Utility Engineering?

A. Subsurface Utility Engineering (SUE) is a highly efficient, nondestructive engineering process that incorporates civil engineering, surface geophysics, surveying and mapping, noninvasive vacuum excavation and asset management technologies to identify and classify quality levels of existing data and maps the locations of underground utilities.

Q. When is locating appropriate?

A. According to the FHWA, locating is sufficient for marking utility facilities immediately prior to excavation or construction.

Q. When is SUE appropriate?

A. SUE is also appropriate in identifying the location of underground utilities prior to construction. SUE is even more appropriate, however, when used during the design phase of a construction project, and, in fact, the FHWA has stated that SUE should be used for design purposes. The information SUE provides contributes to informed design decisions. If SUE data reveals the existence of a utility conflict, those involved in the project find out before any damage is done and can work to develop viable design or utility relocation alternatives to resolve the conflict.

Q. Do locators and Subsurface Utility Engineering providers use the same equipment to locate underground utilities?

A. Not necessarily. Locators generally use a pipe-and-cable device and detect one utility. SUE providers use various geophysical prospecting technologies – such as Pipe-and-Cable Locators, Electromagnetic Imaging (EMI), Acoustical, Pulse, Ground Penetrating Radar (GPR), Three Dimensional Radar Tomography, etc. – to image and detect as many utilities as possible at the site.

Locators, hired by a utility company, typically only provide information on that one utility and visit many sites during the day. Performing SUE investigations take much longer because SUE providers may spend several days at one site to obtain accurate, reliable information on all existing utilities.

All states require contractors to contact “call before you dig” one-call centers prior to construction. These centers notify utility owners, who will contract out or perform locating services within a mandated timeframe that is considered aggressive, thus creating a degree of risk. Many of these states have very “forgiving” tolerances for horizontal accuracy and no standards for vertical tolerances. This may cause information to not be accurate enough for design purposes. Engineers and designers need precise utility information to reduce or eliminate potential design or construction conflicts with utilities.

Q. What is the level of data that locating provides?

A. Locating uses existing drawings showing the location of underground utilities to mark the approximate horizontal location in the work area.

Q. What is the level of data that SUE provides?

A. As the most basic level of information, SUE uses existing records and drawings to identify existing utilities. This information may be appropriate in the very early planning stages of a project because it provides a general overview of utility congestion. However, the information may be inaccurate or out-of-date. Experience has shown time and again that relying on information from old plans and records regarding the location of underground utilities on any construction project may not be the wisest decision. Often, these subsurface facilities are not where the records indicate. In some instances, records are unavailable or nonexistent.

The SUE process does not rely solely on existing records and includes four quality levels of information. It is important to remember that a typical project may not include all four quality levels of information, since the highest level of accuracy may be needed only at those points where conflicts may occur.

The four quality levels of information are:

* Quality Level D –the most basic level of information, based solely on existing records.

* Quality Level C – this is the most commonly used level of information, supplementing Level D information with a visible ground survey of utility facilities, such as manholes or valve boxes. However, SUE industry experts estimate a 15-30% inaccuracy rate for Level C data.

* Quality Level B – this is the first level where SUE designating information is used, supplementing and verifying Level C and D data. This level addresses problems caused by inaccurate utility records, abandoned or unrecorded facilities, or lost references.

The resulting two-dimensional horizontal mapping information is useful during a project’s preliminary design phase, when slight adjustments in the design can produce substantial cost savings by eliminating utility relocations and moving excavation work away from the utilities. At this level, the utility’s vertical position is still not known.

* Quality Level A – this is the highest level of accuracy available, where SUE locating information is added to Level B designating information. Level A provides precise three-dimensional horizontal and vertical mapping of underground utilities and related structures. Small test holes, often just eight inches in diameter at the top, provide a minimum of disruption and intrusion while providing exact information for final design decisions.

These four quality levels are the same as those published by the American Society of Civil Engineers (ASCE) in its Standard Guidelines for the Collection and Depiction of Existing Subsurface Utility Data. They are endorsed by the FHWA and the American Association of State Highway and Transportation Officials (AASHTO).

Q. What are the major Subsurface Utility Engineering activities?

A. The SUE process is tailored to each project and typically includes five major field activities:

* Scope of Work – the process of developing a written project-specific work plan package that consists of scope of work, levels of service vs. risk allocation, project schedule and desired project delivery method. This work plan package is agreed on by the SUE provider and the client.

* Designating – the process of using a surface geophysical method (or methods) to interpret the presence of a subsurface utility and mark its horizontal position – its designation – on the ground surface. Utility owners and contractors sometimes call this process “locating.”

* Locating – the process of exposing and recording the precise vertical and horizontal location of an underground utility. This typically involves nondestructive digging equipment, such as vacuum excavation, at critical points along an underground utility’s path to determine the precise horizontal and vertical position, size and material composition of the underground utility line.

By locating the utility’s precise horizontal and vertical position, project participants can plan for proper protection, eliminate potential damage and safety hazards during construction, and avoid unnecessary and costly utility relocations.

* Data management – the process of surveying the designating and locating utility information to project control and transferring the data into the client’s project CADD files, GIS files or other data representation methods.

* Conflict analysis – the process of using engineering judgment, based on engineering and design best practices, to evaluate and compare depicted utility designating and locating information with proposed plans (highway, bridge, drainage, etc.) to inform all stakeholders of potential conflicts, potential resolutions and costs to cure.

Q. Do SUE providers sign and seal the accuracy of their findings?

A. In accordance with industry best practices, the performance of these five activities listed above allows subsurface utility engineers to sign and seal the resulting information in accordance with the four quality levels, or degrees of risk, described above. Signing and sealing the information means that SUE providers stand behind their findings and take financial responsibility for them.

Q. Do locators sign and seal the accuracy of their findings?

A. We are not aware of any utility owner requiring signing and sealing of “call before you dig” locate data.

Q. Where do the FHWA, AASHTO and State Departments of Transportation (DOTs) stand on the use of SUE?

A. FHWA, AASHTO and the majority of state DOTs use or encourage the use of SUE on all roadway construction projects that involve possible conflicts with underground utilities.

Contrary to what some may believe; SUE and locating providers are not in competition with one another. There is an important place for both. As I stated earlier, the FHWA has made it very clear that SUE should be used during the development of highway projects, and locating should be used prior to excavation. This makes sense because the SUE information is far more accurate and comprehensive and, as a result, more applicable to project designs, whereas locating information provides a visible marking on the ground that provides much better identification of subsurface utility locations than lines on a plan do. It is important to note, however, that steps should be taken to assure that SUE information is provided to impacted utility companies and this information is used for locating.

Rather than being competitors, SUE providers and locators can work together as a team to prevent damage to underground utilities. This will result in substantial financial savings to taxpayers and utility rate payers (who are the same people) and will reduce costly accidents.