Subsurface utility engineering (SUE) is an engineering practice, not a piece of equipment. Defined by the ASCE 38 standard, it's the disciplined process an engineer uses to investigate, verify, and depict what's underground so a project can be designed and built without striking it. SUE sorts utility data into four quality levels: Quality Level D (QL-D) from existing records, Quality Level C (QL-C) from visible surface features, Quality Level B (QL-B) from surface geophysical methods, and Quality Level A (QL-A) — the highest — from physically exposing the utility and measuring it.
QL-A is where OE works. The only way to know exactly where a utility sits, and what condition it's in, is to expose it — and the standard calls for that exposure to be non-destructive. OE digs the test hole with hydrovac: high-pressure water and vacuum open a clean, controlled hole to the utility without striking it, the utility's true horizontal and vertical position is there to be surveyed, and its size, material, and condition can be recorded. The hole is backfilled and the data goes to the team building the SUE deliverable.