Subsurface Utility Engineering (SUE) is an engineering discipline that manages the risks of utility mapping, which primarily includes activities such as the assessment, relocation and design of utilities. SUE also involves the communication of utility data to interested parties, implementation of accommodation policies and estimating the costs of activities related to utility mapping. SUE has historically been largely unregulated, although many countries are beginning to implement standards for it. Standard 38-02 published by the American Society of Civil Engineers (ASCE) specifies the current standards for SUE in the United States.


The use of SUE is becoming more widespread throughout the world as a means of mitigating the costs of damaging underground utilities, including construction delays, project redesigns and liability. This document regulates the practice of collecting, recording and managing data on subsurface structures, especially the pipelines for various utilities. Many countries have developed similar standards, including Australia, Canada, Ecuador, Great Britain and Malaysia. These standards generally classify subsurface utility data according to its reliability, which has become particularly important in developed countries during the last 20 years. This information provides project managers with the ability to assess the value of utility data at the beginning of a construction project.

The first step in a SUE project is the development of a work plan. This plan includes components such as the project’s schedule, its scope, risk allocation and delivery method. Engineers will then use non-destructive surface methods to detect subsurface utilities and mark their approximate locations on the surface. These utilities are then exposed with vacuum excavation and their precise locations recorded as a CAD drawing or GIS map. Engineers use this information to develop a matrix that identifies potential conflicts with project plans and propose solutions.


SUE is primarily used during a capital work project’s design phase or for asset management. The basic process of collecting information is the same in both cases, although the scope and presentation of that information may vary. The primary objective in using SUE in a capital works project is to avoid conflicts later on in the project. For cases involving asset management, project owners generally use SUE to obtain missing information on their underground utilities. The SUE provider then adds this new information to an asset management database based on the quality levels for that jurisdiction.

Quality Levels

The ASCE published Standard 38-02 in 2003, which is entitled “Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data.” This standard establishes guidance of the collection and representation of information on subsurface utilities in the United States. The ASCE standard classifies this data into four quality levels, which indicate the degree of risk when using that information in public works projects. The plans for these projects typically include disclaimers regarding the accuracy of their utility information, and the quality level of that information helps to determine the specific disclaimer used. Quality levels also allow project owners to identify the information they will use to certify the project plans and manage the risks for that project.

ASCE Standard 38-02 recognizes four levels of quality for underground utility information, ranging from Quality Level (QL)-D to QL-A. Information classified as QL-D has the lowest level of accuracy, while QL-A has the highest. This classification system is based on the assumption that not every point in a utility’s path requires the highest level of accuracy, such that a greater number of expected conflicts warrant a higher quality level. For example, the highest number of conflicts typically occurs with highway construction due to the length of these projects.


QL-D Data

QL-D data is the most basic level of utility data. The information at this level comes entirely from existing records or personal recollections, both of which are generally considered unreliable. QL-D data is primarily used to assess the overall concentration of underground utilities, as its use in identifying the location of specific utilities is limited. The most common application of QL-D data is general project planning and route selection.

QL-C Data

QL-C data is probably the most common quality level of utility data. The primary sources for this information include surveys of visible facilities such as manholes and valve boxes, which are typically correlated with QL-D information. This process often identifies utilities that have been incorrectly plotted or are completely missing from the QL-D sources. The most common uses of QL-C data include projects in rural areas, where the repair and relocation of utilities is relatively inexpensive.

QL-B Data

QL-B data comes from surface geophysical methods that precisely locate the position of utilities within a particular area. The primary purpose of this process, also known as “designating,” is to correct inaccurate utility records, including missing references and unrecorded facilities. The proper selection and use of geophysical techniques is critical for the classification of QL-B data, since these are key factors in determining the accuracy of this type of data.

QL-B data is often used to accomplish preliminary goals in engineering projects. For example, it can facilitate decisions regarding the location of proposed design features such as drainage systems, foundations and footers to avoid conflicts with existing features. The value of QL-B data therefore lies in its ability eliminate utility relocations, which can often result in a substantial savings by making slight adjustments to a design.

QL-A Data

QL-A data provides the highest level of accuracy presently available for subsurface utilities. The process of collecting this data is known as “locating” and involves the full use of SUE services to expose utilities through nondestructive means. QL-A data provides highly accurate information on the characteristics of underground features, including their composition, condition, size and type. The most common use of data with this quality level is the precise mapping of utilities, typically for projects in congested urban areas.


Underground Services, Inc. is one of the oldest, full-service SUE companies in the United States. We provide a complete range of SUE services, including our innovative SoftDig® non-destructive excavation system for locating underground utilities.

For more information about the standards that regulate our work, a portfolio of our previous clients or any other question, you may have, get in touch with us at (610) 738-8762 or use our online estimate request form.

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