Who Marks the Private Utilities on a New Jersey Job Site?

How ground penetrating radar contributes — and what it cannot do alone

Ground penetrating radar is one of the tools a private locate uses. It is worth being precise about what it does, because it is frequently oversold.

GPR is, in the US EPA’s description, “an electromagnetic geophysical method that transmits radio wave pulses at select center frequencies into the ground to study the subsurface.” The returning signal’s amplitude and travel time are measured and recorded, and from that a trained operator interprets what is below. The EPA lists locating “pipes, tanks, and other utilities” among its established applications.

Its particular value in private utility work is that it does not require the target to be metallic or traceable. A PVC water line, a fibre-optic duct, an abandoned clay pipe — none of these carry a signal an electromagnetic locator can follow, and all of them can appear in a radar profile.

But GPR has real physical limits, and anyone who tells you otherwise is selling something. From the EPA’s own guidance:

• “GPR is most useful in low electrical loss (i.e., less conductive) materials,” and “signal attenuation is primarily controlled by electrical conductivity.”
• “In environments with surficial layers of saturated clays or saline water, the DOI [depth of investigation] may be limited to centimeter scale.”
• “There is a tradeoff between resolution, which improves with increased signal frequency, and depth of penetration” — the settings that resolve a small target near the surface are not the settings that reach a deep one.
• Most bluntly: “Ideal GPR conditions are rare in nature, and DOI is limited,” owing to the prevalence of conductive groundwater and clay minerals.

In plain terms: wet clay, saturated ground and heavily conductive soils can attenuate the signal severely. Depth and resolution trade against each other. And interpretation is a skill, not an output — the equipment records reflections; a person decides what they mean.

No single geophysical method finds every buried utility. That is not a limitation of GPR specifically; it is the nature of the work. It is also the reason competent locates are not built around one instrument.

NAPCO performs ground penetrating radar surveys across New Jersey, New York and Connecticut, using multi-frequency GPR systems and delivering results as field markings, CAD drawings or 3D models depending on what the project needs.

Why locators combine methods

Understanding how a thorough locate is actually assembled helps you specify one — and helps you read a proposal critically. As an industry practice, private utility locating typically draws on several complementary approaches:

• Records research first. Existing drawings, permits, tenant improvement records and interviews with facilities staff. This is the cheapest information available and it tells the field crew what to look for.
• Electromagnetic locating for conductive lines. Where a line is metallic, or carries a traceable conductor, or can be accessed to receive an induced signal, EM locating is generally faster and more definitive than radar. It is also blind to non-conductive targets — which is precisely where GPR earns its place.
• Ground penetrating radar for the non-metallic and non-traceable, and to image features in the profile that no other surface method will show.
• Vacuum excavation (potholing or daylighting) to physically expose a line where its exact depth and position must be known rather than estimated.

A note on scope, because it matters when you are engaging anyone: electromagnetic locating and vacuum excavation are described here as general industry practice. They are not part of NAPCO’s published GPR service description, and nothing here should be read as a claim that NAPCO performs them. NAPCO’s verified capability, documented on its own service page, is ground penetrating radar survey and reporting. When you scope a locate, ask each provider directly which methods they perform in-house and which they subcontract — and get it in writing.

How to know what your locate is actually worth: utility quality levels

“Locate the utilities” is not a specification. The professional framework that turns it into one comes from subsurface utility engineering, which the Federal Highway Administration describes as a practice combining “civil engineering, surveying, and geophysics.” Its four utility quality levels are codified in the ASCE standard ASCE/UESI/CI 38-22, Standard Guideline for Investigating and Documenting Existing Utilities, and FHWA defines them as follows:

• Quality Level D — “The most basic level of information for utility locations. It comes solely from existing utility records or verbal recollections, both typically unreliable sources.”
• Quality Level C — “Involves surveying visible utility facilities (e.g., manholes, valve boxes, etc.) and correlating this information with existing utility records.”
• Quality Level B — Applies “surface geophysical methods to determine the existence and horizontal position of virtually all utilities within the project limits.”
• Quality Level A — “The highest level of accuracy presently available… It provides information for the precise plan and profile mapping of underground utilities through the nondestructive exposure of underground utilities.”

Two things follow from this list that are worth internalising.

First, most people asking for a “utility locate” are describing Quality Level B — surface geophysics establishing that something exists and where it runs horizontally. GPR and EM locating operate at this level. That is often exactly what a project needs.

Second, if you need to know depth precisely, you are asking for Quality Level A, and that requires physically exposing the line. No surface method delivers QL-A. Specifying the level you actually need, rather than the service you assume exists, is the single most useful thing an engineer or project manager can do at scoping.

Before you dig: a sequence for New Jersey sites

1. File the One Call ticket — not less than three and not more than 10 business days before you break ground, and remember it stays valid for 45 business days only if you maintain the markout.
2. Walk the site before the crew arrives. New Jersey One Call’s own guidance is that a thorough excavator inspects the jobsite before submitting the request, speaks with the property owner about equipment and power sources, looks for surface evidence, and contacts whoever installed the original facilities to check for records or maps.
3. Ask the property owner or tenant directly what they own underground. They carry the responsibility for locating private facilities, and they frequently know about lines that appear on no drawing.
4. Gather and date the records. Note what the as-builts do not cover as carefully as what they do.
5. Decide whether private facilities are in scope, and if so, commission a private locate with a defined deliverable and a defined quality level — not just “come mark the site.”
6. Reconcile the two sets of marks. Public markout and private locate should be read together, and disagreements between them investigated rather than averaged.
7. Respect the tolerance zone. No mechanised equipment within two feet horizontally of a marked facility until it has been located by hand.
8. Document what was found before it is buried again. A locate that exists only as paint on asphalt is gone with the next rain. A CAD or model deliverable becomes part of the record set — and is worth considerably more to the next crew on the site than the marks were.

Frequently asked questions:

Does New Jersey One Call mark private utility lines?

Not unless the facility’s owner is a participating member. New Jersey One Call states that “unless the private facility owner participates as a member of NJOC, owners of private facilities are not notified and will not mark.” The centre routes notifications to registered operators; it does not perform markouts itself.

Who is responsible for locating private utilities in New Jersey?

The property owner or tenant. New Jersey One Call’s guidance is explicit: “When a property owner or tenant has any private underground facility, they are responsible for locating those facilities or hiring someone to locate them.”

How much notice do I have to give before excavating in New Jersey?

Not less than three business days and not more than 10 business days before beginning excavation or demolition (N.J.S.A. 48:2-82(a)). The notice remains valid for 45 business days provided the markout is maintained.

How close to a marked line can I use mechanised equipment?

No closer than two feet horizontally from the outside wall of a marked facility, unless the facility has first been located by hand digging (N.J.S.A. 48:2-82(d)(1)).

Can ground penetrating radar find every buried utility?

No. GPR performs best in low-conductivity ground; the EPA notes that saturated clays or saline conditions can reduce its depth of investigation dramatically, and that “ideal GPR conditions are rare in nature.” It is one method among several, and it is most effective when paired with records research and complementary locating techniques.

Does a utility locate tell me how deep the line is?

Surface geophysical methods establish existence and horizontal position — Quality Level B in the FHWA framework. Precise depth requires Quality Level A, which involves physically exposing the utility. Specify the level you need at scoping.

What do I actually receive at the end of a private locate?

That depends on what you specify, which is why it belongs in the scope. NAPCO’s GPR surveys can be delivered as field markings on site, as CAD drawings, or as 3D models — the GPR service page sets out what each deliverable includes.

Planning excavation on a New Jersey site?

If you are planning excavation, boring, drilling or pile work and the public markout may not account for everything on the property, the private lines are still someone’s responsibility — and on private property, that someone is usually you or your client.

NAPCO has supported New Jersey, New York and Connecticut construction and engineering projects since 1946. To discuss whether a GPR survey fits your site conditions and scope, tell us about the project. If the findings need to become part of a permanent record set rather than paint on a slab, 3D laser scanning can document existing conditions alongside the subsurface work.