The Four Quality Levels of Subsurface Utility Engineering

The American Society of Civil Engineers (ASCE) created and published the document “Standard Guidelines for the Collection and Depiction of Existing Subsurface Utility Data”, also known as the four quality levels of Subsurface Utility Engineering (SUE). This document created standard practices across the industry for collecting and depicting SUE information.

The quality levels were created to better match SUE services to the needs of a particular project. By classifying the quality levels, project owners, engineers, and contractors are able to better understand their levels of quality and develop strategies to reduce or allocate risks.

The following is an explanation of each quality level as described by the ASCE:

Quality Level A: Designating & Locating – Recommended during the design and construction phases

• Precise horizontal and vertical location of utilities obtained by the actual exposure and subsequent measurement of subsurface utilities, usually at a specific point. A precise horizontal and vertical location, as well as other utility attributes, is shown on plan documents. Accuracy is typically set to 15-mm vertical and to applicable horizontal survey and mapping accuracy as defined or expected by the project owner.

Quality Level B: Designating Only – Recommended during early design stages and in areas where utility records are generally unreliable

• Information obtained through the application of appropriate surface geophysical methods to determine the existence and approximate horizontal position of subsurface utilities. Data should be reproducible by surface geophysics at any point of their depiction. This information is surveyed to applicable tolerances defined by the project and reduced onto plan documents.

Quality Level C: Visible Features – Recommended during project planning stages to aid site layout decisions

• Information obtained by surveying and plotting visible above-ground utility features and by using professional judgment in correlating this information to quality level D information.

Quality Level D: Records Review – Recommended for feasibility studies during the pre-design stage to help identify potential costly utility relocations

• Information derived from existing records or oral recollections.

Each level of quality, as set forth by the ASCE, pertains to the methods, interpretation, and precision of the subsurface utility data collected. The quality levels are intended to serve as a guide for engineers to determine the level of detail they require to realize the greatest benefit from SUE services. Since the publication of the standards by the ASCE, governmental organizations responsible for authorizing utility and excavation work are beginning to require at minimum a quality level B prior to excavation.