Private Utility Locating & Concrete Scanning

Why private locating exists: what MISS DIG doesn't mark

A MISS DIG 811 notice goes to member facility owners, who mark their own facilities. MISS DIG states that private utility lines not installed by the utility company will not be marked, but can be marked by private locating companies for a fee (MISS DIG 811 Digging FAQs). Its examples include lines to a grill or shed, sprinkler systems, and invisible dog fences. On commercial and industrial sites, private lines often include:

• Site lighting and parking-lot electrical, gate and sign feeds
• Lines between buildings on a campus, plant, or farm
• Private water services, storm and sanitary laterals on the owner's side
• Fire lines, irrigation, fuel lines, and tank piping
• Owner-installed fiber, security, and communications cable

MISS DIG also notes that locators mark approximate location, not depth. That's why the law requires soft excavation within the 48-inch caution zone. How MISS DIG works →

How private locators find lines

Electromagnetic (EM) locating

An EM locator detects the magnetic field from alternating current flowing on a conductive line. The signal can be passive (already present on the line) or applied by the locator's transmitter, either by direct connection or by induction. EM works well on continuous metal pipes and cables, and on non-metallic pipes that have a tracer wire. PVC, fiberglass, vitrified clay, and insulated sections usually can't be traced without a tracer wire, or a sonde or fish tape pushed inside the pipe (FHWA: Site Characterization and Utility Locating).

Ground penetrating radar (GPR)

GPR sends radar pulses into the ground and records reflections from changes in material properties. It can detect metallic and non-metallic lines and backfilled trenches. Its big limitation matters in Michigan: moist soils and clay attenuate the signal and can sharply limit depth, and GPR can't see beneath metal (FHWA InfoTechnology: GPR for underground utilities; FHWA: Site Characterization and Utility Locating). In heavy clay, which is common in Southeast Michigan, GPR may miss lines that EM or a test hole would find.

Records and visual survey

Good locators also review as-builts and walk the site for clues like meters, valve boxes, cleanouts, light poles, and patched pavement.

Pairing a locate with hydro excavation

Surface methods tell you where a line probably is. Exposing it tells you where it actually is. The engineering standard for utility investigations, ASCE/UESI/CI 38-22, describes this as quality levels:

• QL-D: existing records only
• QL-C: records plus a survey of visible features
• QL-B: geophysical "designating" with EM, GPR, and similar methods to establish horizontal position
• QL-A: physically exposing the utility, typically by non-destructive vacuum excavation, and surveying its horizontal and vertical position

(FHWA summary: FHWA: Subsurface Utility Engineering (ASCE/UESI/CI 38-22 quality levels).) A common workflow is a private locate to mark candidates, then hydrovac potholes at crossings and conflict points to confirm depth, size, and material before boring or trenching.

Concrete scanning before coring or cutting

Before core drilling, saw cutting, or anchoring into a slab or wall, contractors scan the concrete to find rebar, conduit, and post-tension (PT) tendons. GPR is the most common method, and its rebar reflections show up clearly in scan data (FHWA InfoTechnology: GPR for underground utilities). Other tools include electromagnetic cover meters and, in some cases, X-ray radiography, which involves ionizing radiation and requires clearing the area.

• Post-tensioned slabs: Industry guidance says to locate tendons in place (by GPR or other detection), mark them, and confirm the planned hole avoids them. Drawings and soffit marks are only a guide. If a tendon might be cut, stop and involve the engineer (Post-Tensioning Institute of Australia, Guidance Note: Post-Cut Holes through Post-Tensioned Slabs).
• Conduit in slabs: Live electrical conduit in elevated and on-grade slabs is a shock and outage hazard for coring crews.
• Limits: Dense rebar mats can mask what's beneath them. Scan results are an interpretation, so ask how findings will be marked and documented.

Requesting this service

Use the form and note "private locate" or "concrete scanning" in the job details. Include the site address, area to be cleared, what you're installing or coring, and your MISS DIG ticket number if you have one. We'll pass it to an independent provider who covers that part of Michigan. Some hydrovac operators offer locating; others partner with locating firms.

Sources: MISS DIG 811 Digging FAQs; FHWA: Site Characterization and Utility Locating; FHWA InfoTechnology: GPR for underground utilities; FHWA: Subsurface Utility Engineering (ASCE/UESI/CI 38-22 quality levels); Post-Tensioning Institute of Australia, Guidance Note: Post-Cut Holes through Post-Tensioned Slabs; MISS DIG Underground Facility Damage Prevention and Safety Act, 2013 PA 174 (MCL 460.721–460.733).