Subsurface Utility Engineering

Subsurface Utility Engineering (SUE) involves managing certain risks associated with utility mapping. Elements of SUE include utility coordination, utility relocation design and coordination, utility condition assessment, communication of utility data to concerned parties, utility relocation cost estimates, implementation of utility accommodation policies, and utility design.

SUE site condition assessments are characterized by Quality Level- in general, the preciseness of the utility underground location assessment, and level of excavation risk present. SUE involves four Levels of site condition assessments, from the least precise (called Quality Level D assessments in which the utility location is derived from existing records and oral recollection), to the most precise (called Quality Level A assessments that enables extremely accurate utilities location placement and use of minimally intrusive excavation equipment to minimize the potential for damage to the underground utility).  Each Quality Level is further described below. Each ascending level approach includes the subordinate levels.

Quality Level D – Information derived from existing records and oral recollection.

Quality Level C – Additional 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 B – Additional information obtained through the application of appropriate surface geophysical methods to determine the existence and approximate horizontal position of subsurface utilities. Quality Level B information 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 into documents. United Consulting typically employs a level of accuracy for Quality Level B of approximately ± 12 inches on both the horizontal and vertical axis.

Quality Level A – In addition to information found within  Quality Levels D, C, and B, precise horizontal and vertical location of utilities are obtained by the actual exposure (or verification of previously exposed and surveyed utilities) and subsequent measurement of subsurface utilities, usually at a specific point. Minimally intrusive excavation equipment is typically used to minimize the potential for utility damage. A precise horizontal and vertical location, as well as other utility attributes, is shown on plan documents. Accuracy is typically set to 0.5 inches vertical and to applicable horizontal survey and mapping accuracy as defined or expected by the project owner.

United Consulting performs both Level B and Level A SUE services. Our clients most often do see reductions in project cost and associated project risk when pursuing Level B and Level A services. During a Level B investigation, the horizontal and vertical location of underground utilities are indicated using surface geophysical techniques such as Ground Penetrating Radar (GPR), electromagnetic, magnetic or other energy fields. Electromagnetic methods include the following: pipe and cable locators (inductive, conductive, active, and passive modes), terrain conductivity, ground penetrating radar, ground resistivity techniques, optical methods, and computer-driven algorithms coupled with data collection techniques. This method usually provides adequate, acceptable utility location data. However, if problems are encountered during the Level B investigation, a Level A vacuum exploration can be performed. Level A investigations involve locating the precise horizontal and vertical positions of utilities by excavating a test hole to expose the utility. A vacuum excavation method is then employed to minimize the possibility of damage to a utility line.