The Difference Between SUE Results and SUE Value: Understanding the Difference Between What Was Found and What Was Learned

Imagine you are a project stakeholder reviewing an SUE deliverable.

The scope included Quality Level B (QL-B) designating throughout the project area and 20 Quality Level A (QL-A) test holes at locations important to the design. When the deliverable arrives, only 15 of those test holes resulted in successful utility exposures. The other five contain some version of either: No utility found / Unable to verify.

While excavating two of the successful test holes, the crews also encountered utilities that were not previously identified during the QL-B investigation. The client wants to know:

• I paid for QL-B. Why were those utilities not found?

• I ordered 20 test holes. Why am I being charged for five locations where you did not expose anything?

• If you missed utilities during QL-B and could not find five of the utilities during QL-A, did I actually receive the SUE services I paid for?

Those are fair questions. They also highlight one of the biggest misunderstandings I continue to see surrounding SUE investigations:

We sometimes treat a SUE investigation and the results of that investigation as though they are the same thing. They are not.

What Are We Actually Purchasing?

This is not an argument for which SUE providers should be held accountable.

If a provider did not perform a thorough investigation, use appropriate equipment, review available evidence, investigate inconsistencies, or complete the agreed-upon scope, that is a different conversation.

We should absolutely be accountable for the quality of our work.

But accountability for the investigation is different from guaranteeing the result of that investigation.

When we perform SUE, we are investigating an environment we cannot completely see using technologies that all have physical limitations.

We use records, visual evidence, electromagnetic locating equipment, ground penetrating radar, sondes, rodders, vacuum excavation, and survey, combined with field experience, and professional judgment to develop the best information reasonably supported by the investigation.

Sometimes that investigation gives us a very clear answer. Sometimes it doesn't. This is where our industry has an opportunity to better explain what SUE is intended to provide.

A client isn't purchasing a guarantee that every utility underground will be found. They are purchasing a defined professional investigation intended to reduce uncertainty about what is underground and provide the best defensible information that investigation can support.

There's a big difference.

When a Missed Utility Is Not Automatically a Failed Investigation

Remember the two utilities that were not identified during QL-B but were later discovered while excavating for QL-A? It's easy to look at that result and immediately conclude that QL-B missed two utilities.

Maybe it did, which is exactly where an investigation into the investigation should begin.

• Were the utilities detectable?

• Was there visible evidence of them?

• Were they shown on records?

• Were appropriate electromagnetic connection methods attempted?

• Was GPR used where appropriate?

• Was the site investigated from multiple directions?

• Were there structures, valves, meters, pedestals, handholes, cleanouts, or other evidence that should have caused the technician to investigate further?

• Were there questionable signals that should have been followed?

If the answers to those questions show that reasonable evidence was overlooked or appropriate investigative methods were not performed, then we may have a quality issue.

But there's another possibility. The utilities simply may not have produced enough evidence to be identified during the QL-B investigation.

Maybe:

• It was a nonconductive service without tracer wire

• The tracer wire was broken

• The utility was significantly deeper than anticipated

• The electromagnetic response coupled onto another facility

• The soil conditions limited GPR effectiveness

• GPR produced an anomaly, but there was not enough information to responsibly interpret that anomaly as a utility.

These possibilities don't automatically prove the QL-B investigation was performed correctly either. They mean we need to understand how the investigation was performed before judging it solely by the eventual result. That's an important distinction.

Detection Is Not the Same as Existence

One of the easiest traps in utility investigation is treating our equipment as if it directly tells us what is underground. It doesn't.

Our equipment gives us information that we interpret. An electromagnetic receiver is not seeing a pipe. It is detecting and interpreting an electromagnetic field. A GPR antenna is not showing us a photograph of a utility. It is transmitting energy into the ground and displaying reflected energy that we then interpret.

When we vacuum excavate, we are finally introducing a physical observation into the process—but even excavation has limitations involving depth, soil conditions, groundwater, access, safety, and the ability to effectively remove material.

That's why three simple statements are worth remembering:

• Detection does not always equal identification

• Non-detection does not prove absence

• Investigation does not guarantee a predetermined result

Depth Changes Everything

Depth is probably one of the best examples of why these distinctions matter. Take electromagnetic locating. Let us say we are investigating a nonconductive utility with a tracer wire. We have access to that tracer wire, it is continuous, and it is bonded at both ends.

From the surface, the signal looks great. It's strong. It's repeatable. We can follow it. The receiver is giving us an indicated depth of five to six feet. If you are standing in the field looking at that response, you may have every reason to believe you have a solid locate.

Then we return to perform the QL-A test hole. We excavate to six feet. And we find Nothing.

Continuing the investigation, we check the designation again. Eventually, we lower the receiver into the test hole. Now something interesting happens. The same signal that appeared to be five or six feet deep from the surface suddenly indicates that the facility may actually be another five feet below us. We are potentially looking at a utility 10 or 11 feet deep.

What happened?

The pipe didn't move.  Our understanding of the information changed.

The electromagnetic field we were interpreting from the surface may have been distorted, coupled, bleeding onto another conductive pathway, or otherwise influenced by the surrounding environment. That's an important lesson:

A strong signal is not necessarily the same thing as a high-confidence result.

And as utilities get deeper, these challenges can become much more significant.

GPR Has the Same Problem—Just in a Different Way

When the EM locater does not give us the answer we need, one of the tools we often turn to is ground penetrating radar (GPR). This is another place where expectations sometimes get ahead of the technology.

I've heard versions of this plenty of times:

“Did you run GPR?”

Yes.

“Then why did you not see it?”

Because GPR is not an underground X-ray.

GPR, commonly used for utility locating, operates across a range of frequencies selected for the site conditions, target depth, target size, and required resolution. There is a tradeoff. Lower-frequency antennas generally provide greater depth penetration but lower resolution. Higher-frequency antennas generally provide better resolution for shallow targets but reduced effective investigation depth. That's a major consideration when we're looking for utilities.

It doesn't do us much good to say that radar energy can penetrate to a certain depth if we don't have enough resolution at that depth to confidently identify the target we're looking for. Likewise, a high-frequency antenna may give us a beautiful image of shallow features while simply not providing useful information at the depth of a much deeper utility.

Then add soil conditions. Clay, moisture, groundwater, pavement, reinforcement, disturbed soils, trench backfill, target size, target material, and surrounding infrastructure can all influence what comes back to us. Sometimes we get a textbook hyperbola. Sometimes we get something that tells us there is definitely something going on there.

And sometimes we get nothing useful at all.

That's why:

No identifiable GPR response was observed does not mean there is nothing underground.

It means exactly what it says: under the conditions encountered, using the equipment and methods applied, we did not identify a response we could confidently associate with a utility. Those are very different statements.

Why an Unsuccessful Test Hole Can Still Provide Value

This brings us back to our original stakeholder. Twenty QL-A test holes were requested. Fifteen utilities were successfully exposed. Five came back Unable to Verify.

The better questions are whether or not a defensible investigation was performed at those five locations, whether the limitations were clearly documented, and whether the remaining risk was communicated in a way the project team can use.

Because what was purchased was not twenty guaranteed utility exposures. What was purchased was the professional investigation necessary to attempt to obtain QL-A information at twenty locations. That distinction should be communicated during scoping, not after the invoice arrives.

A crew still mobilized to those locations. They re-designated the target, excavated, investigated the surrounding area, used specialized equipment and trained personnel, and may have expanded the excavation, checked adjacent signals, changed excavation methods, or performed additional geophysical investigation to understand why the anticipated utility was not where the available evidence suggested it should be.

And sometimes, despite all that effort, the responsible answer is: Unable to Verify.

But there's another important distinction here. If the utility was never physically exposed, we shouldn't represent that location as though QL-A information was successfully obtained. We performed the investigation attempting to obtain QL-A information. The investigation was unsuccessful in physically verifying the utility at that location.  That's still a result. And sometimes it's an extremely important one.

QL-A Has Physical Limitations Too

The deeper we go, the more difficult excavation becomes. Vacuum excavation is an incredibly effective tool, but it is not unlimited.

As test holes become deeper, vacuum excavation can reach a practical limit where soil conditions, groundwater, excavation diameter, collapsing material, access, and equipment capacity make continued excavation difficult to perform safely and effectively.

At six feet, excavation may be progressing beautifully. At 10 or 12 feet, the exact same equipment in the exact same location may struggle considerably. This is where locating and excavation limitations can overlap in practice—not because they are the same limitation, but because one can reveal the other.

We originally believed the utility was approximately six feet deep. We excavated to six feet and did not find it. Additional investigation now suggests it may actually be 10 or 11 feet deep. At some point, the question isn't simply: Can we keep digging?

It's: Can we continue this investigation safely, effectively, and responsibly with the equipment and conditions we have?

Sometimes the answer is no. That doesn't necessarily mean the investigation failed. It means the investigation identified a limitation.

“Unable to Verify” Can Be Valuable Information

This may be the hardest concept to communicate. Sometimes a good investigation tells us that we know less with certainty than we originally thought. Before our test hole, the design team believed there was a utility at a particular horizontal location approximately six feet deep. After the investigation, we may know:

• The utility was not encountered at six feet

• The original EM depth appears unreliable

• Additional geophysical evidence suggests the utility could be substantially deeper

• The utility could not be physically exposed within the practical limitations of the excavation performed

We didn't get the QL-A information we wanted. But we learned something incredibly important: There's unresolved utility risk at this location.

• It can change the design

• It can justify another test hole

• It can trigger coordination with the utility owner

• It can change how excavation is approached during construction

• It can cause the engineer to increase clearance

• It can tell the contractor, “We do not know exactly where this utility is, and you need to plan accordingly.”

That is not worthless information. That's exactly the type of uncertainty SUE is supposed to help identify.

But This Can’t Become an Excuse

There is an important flip side to everything I have said. We cannot allow SUE is an investigation to become an excuse for poor investigations. A technician cannot walk onto a site, connect to two obvious utilities, sweep the area, paint what responds, and say: “That's everything I could find.”

A test-hole crew cannot dig directly on a mark, reach the anticipated depth, fail to find the utility, and immediately write: Unable to Verify. There has to be a defensible level of effort behind those conclusions.

Did we investigate the records?

Did we look for physical evidence?

Did we attempt appropriate connection methods?

Did we investigate from multiple directions?

Did we use complementary technologies where appropriate?

Did we question signals that didn't make sense?

Did we re-designate after an unsuccessful excavation?

Did we document the conditions and limitations?

Did someone with appropriate experience review questionable results?

That's where accountability belongs.

We cannot guarantee what exists underground or guarantee that every utility will respond to the technologies available to us.

We can be accountable for how thoroughly and professionally we investigate it.

And, SUE is still the safest and most reliable method available.

Setting Expectations Before the Work Begins

This brings me back to our frustrated project stakeholder. If the first meaningful conversation about these limitations happens after the deliverable is submitted and the invoice arrives, we have already created a problem.

The bigger opportunity for the SUE industry isn't simply improving our technology. It’s improving how we communicate what we're actually providing.

QL-B should not be sold or understood as: We will find every utility.

And requesting 20 QL-A test holes should not automatically be understood as: You will receive 20 successfully exposed utilities.

Instead, we need to explain the investigation, the expected level of effort, the technologies involved, the applicable limitations, and how unresolved conditions will be documented. The quality levels used in recognized SUE standards describe the source and reliability of utility information; they should not be interpreted as a guarantee that every utility will be found or physically exposed.

That conversation protects everyone. It gives the client realistic expectations. It holds the SUE provider accountable for performing a thorough investigation. And most importantly, it prevents uncertainty from being hidden behind a quality-level designation.

Where the Real Value of SUE Lies

Ultimately, SUE exists because uncertainty exists. If we already knew, with confidence, where every utility was located, how deep it was, what material it was made of, and where every conflict existed, there would be little need for a SUE investigation.

But, we are brought into projects because the underground environment is incomplete, imperfectly documented, and often more complex than the available records suggest.

Our responsibility is to reduce that uncertainty through a defensible process, not to pretend we can eliminate it entirely. Sometimes that value appears as a line on a map. Sometimes it appears as a measured depth from a successful test hole. And sometimes it appears as a clearly documented limitation that tells the project team where risk remains and where additional care, coordination, or design consideration is warranted.

That may not always be the result the stakeholder hoped for, but it can still be valuable information—provided the investigation was thorough, the limitations were clearly explained, and the conclusions were honestly communicated.

So, when we evaluate SUE, the question should not only be: Did you find it?

It should also be: Did you investigate it properly, and did you clearly tell me what you know, what you do not know, and why?

Because the value of SUE is not measured only by what was found. It is measured by whether the investigation helped the project team make better decisions about what is known, what remains uncertain, and how that uncertainty should be managed.

That is the difference between SUE results and SUE value.