Availability, Feasibility, 

and Reliability of Available 

Nondestructive Evaluation 

Technologies for Detecting 

and Locating Buried Utilities

FHWA Publication No.: FHWA-HRT-22-111

FHWA Contact: Frank Jalinoos (ORCID: 0000-0001-8330-7603), HRDI-30, 

(202) 493-3044, frank.jalinoos@dot.gov.

This document is a technical summary of the Federal Highway 

Administration report on the Availability, Feasibility, and Reliability of 

Available Nondestructive Evaluation (NDE) Technologies for Detecting 

and Locating Buried Utilities (forthcoming).

OBJECTIVE

The Federal Highway Administration (FHWA) conducted research on the use 

of promising nondestructive evaluation (NDE) techniques for the detection of 

buried underground utilities (Reiter et al. forthcoming). The research objectives 

were as follows:

• Identify promising technologies that merit expanded application and 

mainstream deployment by State departments of transportation (DOTs).

• Assess the capabilities of NDE technologies under controlled laboratory 

conditions to establish performance baselines and compare the strengths 

and weaknesses of each technique.

• Conduct real-world field tests of NDE technologies at sites with 

well-documented locations of buried utilities.

• Recommend NDE technologies by describing their ideal parameters 

and testing conditions and determining the advantages and limitations 

of each one.

KEY TAKEAWAY

The most promising researched and tested technologies were step-frequency 

and multifrequency ground-penetrating radar (GPR), frequency-domain 

electromagnetic (FDEM) method, and multichannel analysis of surface 

waves (MASW).

INTRODUCTION

Modern NDE technologies offer an expanding suite of geophysical techniques 

to detect and locate buried utilities. This project focused on identifying 

promising technologies that merit expanded application and mainstream 

deployment by State DOTs. Since the Second Strategic Highway Research 

Program (SHRP 2) Project R01: Encouraging Innovation in Locating and 

Characterizing Underground Utilities was published in 2009 (Sterling et 

al. 2009), new approaches in GPR and acoustic technology have become 

TECHBRIEF

Research, Development, 

and Technology

Turner-Fairbank Highway 

Research Center 

6300 Georgetown Pike 

McLean, VA 22101-2296

https://highways.dot.gov/research
2

more widely available, while other electromagnetic 

and seismic methods have been identified as worth 

further investigation. Building on SHRP 2, the project 

team researched, identified, and tested various NDE 

technologies to compile a concrete recommendation 

plan for each method investigated.

METHODOLOGY

The first phase of this project involved an indepth 

literature review to identify current and emerging 

NDE technologies that could improve the detection 

and location of underground utilities. The project team 

reviewed technologies across four geophysical domains: 

electromagnetic, magnetic, acoustic, and seismic 

(figure 1). The team gathered capability information 

for NDE mapping techniques across a diverse array 

of conditions and applications. Some of the identified 

NDE technologies, such as traditional GPR methods 

and pile-and-cable locators, have already been broadly 

deployed in subsurface utilities location projects. Other 

technologies, such as step-frequency GPR and MASW, 

show increasing promise in field tests and continue 

to undergo improvements in data acquisition and 

high-resolution mapping.

In the project’s second phase, the team assessed the 

capabilities of NDE technologies under controlled 

laboratory conditions to establish a performance baseline 

and compare the strengths and weaknesses of each 

technique. The project team built a set of soil-filled 

enclosures and emplaced utility pipes of varied types, 

depths, and diameters in different soil conditions and 

burial configurations. NDE technologies from the four 

geophysical domains were tested to determine their 

baseline characteristics in the soil enclosures.

The last phase of the project included real-world 

field tests of five NDE technologies at sites having 

well-documented locations of buried utilities with 

different material types and emplacement conditions.

INFORMAL POLLING OF STATE DOTS

To ensure the true needs of the States were considered 

during the investigation of current and emerging NDE 

technologies, the project team polled representatives 

from nine State DOTs for their input on what approaches 

and technologies they use in buried utility location. The 

following questions are examples from the poll:

• Do you deploy NDE technologies internally 

or outsource the work? 

• What are the most reliable data-processing methods? 

What are the challenges?

• Which NDE technologies do you use regularly? 

Which technologies do you trust?

• What are the most significant factors when 

considering new technologies (e.g., cost, training, 

processing time, reliability)?

Using both a written and verbal polling process, the 

project team received a significant amount of informative 

feedback from the State DOT offices. Some key findings 

included the following:

• States consistently place their highest trust in GPR 

technology and traditional line locators.

• The precision and accuracy of NDE technology 

are the most important factors when considering 

new technologies. 

• Interest exists in the development of new NDE 

technologies and automated systems.

• Most States are challenged by the need for roadway 

closures with nonvehicle-mounted technology.

CONTROLLED LAB TEST 

OF NDE TECHNOLOGIES 

While the literature search and industry review yielded 

important findings on the state and availability of modern 

NDE technologies for locating buried utilities, the next 

step in this study evaluated several technologies side 

by side to determine their efficacy under controlled 

test conditions. The methods selected for evaluation 

during this part of the project included GPR, FDEM, 

horizontal-to-vertical spectral ratio (HVSR), and acoustic 

pipe locator (APL). They were chosen for their ability to 

be used on grade without the need for utility exposure, 

Figure 1. Graphic. Overview of methods 

researched and evaluated.

Source: FHWA.

• GPR (multifrequency and step-frequency).

• Cable and pipe locators. 

• Time-domain electromagnetic (TDEM) and FDEM. 

Electromagnetic

• Magnetic locators.

• Magnetometers. Magnetic

• Acoustic pipe locator.

• Pipe excitation method. 

• Distributed acoustic sensing.

Acoustic

• Horizontal-to-vertical spectral ratio.

• Spectral analysis of surface waves.

• MASW.

Seismic
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their relevant equipment and systems being readily 

available in the market for use, and their established 

procedures and processes for deployment. 

The project team developed a laboratory testing plan 

to thoroughly evaluate each of the different selected 

NDE technologies. To assess the effectiveness of each 

NDE technology in a controlled setting, a matrix of 

specimens was designed and tested using typical utility 

pipes of varying sizes buried in different soil conditions 

and burial configurations. A combination of soil-filled 

enclosures was also designed, built, and tested under 

different controlled configurations. Four specimen types 

were investigated: fine-grained cohesive soil, coarsegrained cohesionless soil, two layers of cohesive soil at 

the bottom and cohesionless soil on top, and two layers of 

cohesionless soil at the bottom and cohesive soil on top. 

The laboratory specimens were designed and built at 

a North Carolina DOT (NCDOT) indoor facility in 

coordination with the NCDOT Materials and Test Unit. 

Nine utilities of varying materials and dimensions were 

buried in each enclosure. Utility pipes were placed into 

holes on each side of a given base frame such that they 

entered one side of the base and exited the other side 

(figure 2).

The project team found GPR to be the most effective of 

all the methods evaluated in this test bed environment. 

GPR was capable of successfully locating both polyvinyl 

chloride (PVC) and metallic pipes down to 6-ft depths 

(figure 3). GPR fared better on the cohesionless soil 

compared to the cohesive soil due to moisture retention 

in the soil, which introduces noise. FDEM was successful 

at detecting metallic buried utilities at up to 2-ft depths. 

Relative conductivity measurements for the steel pipes 

decreased with increasing pipe depth. The APL and 

HVSR techniques were inconclusive in this setting, which 

may be due to reflections off the side of the soil boxes 

interfering with the signals of interest.

REAL-WORLD FIELD EXPERIMENT 

OF NDE TECHNOLOGIES

Based on the results from the controlled lab experiments, 

the team field-tested a variety of NDE technologies in 

southern Virginia. The Virginia DOT (VDOT) identified 

field sites with well-documented buried utilities and 

accessible locations for NDE technology tests. VDOT 

provided a list of possible field sites with buried utilities 

that varied in material type (PVC versus metal), diameter, 

and depth (shallow versus deep). The field team selected 

three VDOT-approved locations with similar sets 

of buried utilities, including PVC water and sewage 

pipes from 1 to 10 ft below the ground surface. Field 

testing focused on four NDE technologies, including 

two electromagnetic techniques (step-frequency GPR 

and FDEM) and two seismic/acoustic techniques 

(MASW and APL).

GPR RESULTS

Several general observations can be made about the 

performance of the multifrequency GPR system, GSSI 

UtilityScan®, at the three field sites. First, the system 

performed GPR scans in nonideal environments with 

varying and uneven surface conditions without a 

Figure 2. Illustration. Soil box specimen.

Source: FHWA.

⌀ = diameter; PVC = polyvinyl chloride. 
4

reduction in data quality or system performance. The 

UtilityScan GPR is easy to operate. A single technician 

can push the antenna cart along a scan line and review 

data in realtime. Second, the UtilityScan system uses a 

dual-frequency antenna that produces two channels of 

output at different frequencies, which provides better 

resolution of subsurface features. For example, the 

UtilityScan system detected PVC water lines at relatively 

shallow depths despite the nonconductive material type. 

However, the system did not consistently detect PVC 

water lines at relatively deep depths, most likely because 

of the increased depth of pipe and the nonconductive pipe 

material type.

In contrast, the KontūrTM 3D-Radar GPR system did not 

perform as well as the UtilityScan GPR system. Although 

the 3D-Radar GPR is deployable in high-traffic settings 

and at typical roadway speeds, it requires considerable 

setup and tuning to ensure high-quality data collection. 

The system benefits from GPS data encoding, which is 

an advantage over the UtilityScan GPR system, because 

it minimizes the need for handwritten field notes on 

scan-start and scan-stop positioning. The Kontūr system 

also detected PVC water lines at relatively shallow depths 

Figure 3. Image. GPR scans collected on cohesive soil test specimens. 

Source: FHWA.

despite the nonconductive material type, but it did not 

detect the deeper PVC water lines due to nonconductive 

pipe material and the increased depth of the utility lines.

MASW RESULTS

MASW technology can detect and approximately locate 

utility lines, particularly with the right acquisition 

strategies. In particular, using “shoot-through” or 

roll-along MASW acquisition strategies led to clear 

detections of utilities at one of the VDOT sites. This 

setup involves moving and striking the hammer source 

at a set interval across the entire 24-geophone array. 

Geophone spacing and the appropriate source weights are 

key parameters for a successful application of MASW 

to detect buried utilities. Using this application, the field 

team found that a 1.5- to 4-lb hammer weight and 1- to 

3.3-ft geophone spacing were optimal for utility detection 

at depths from 3 to 10 ft. 

Located utilities included 4-inch diameter water lines at 

3.3- and 4-ft depths and an 8-inch diameter sewer line 

at a depth of 10 ft (figure 4). Using the shoot-through 

approach produced accurate results within 1–3 ft of 

the known buried depth. Because only the successful 
5

shoot-through approach was used on 3 out of 26 tested 

buried utilities, additional research is recommended to 

validate the success of the technique. Additionally, while 

the MASW method can successfully image the locations 

and depths of buried utilities, it is unable to resolve pipe 

diameters with confidence. The MASW technology is not 

suitable as a standalone detection method of underground 

utilities without further research, but it can be used as 

an auxiliary method to increase confidence in the results 

from other NDE technologies or as an alternative method 

when GPR or other methods are unsuccessful.

RECOMMENDED NDE TECHNOLOGY 

AND NEXT STEPS

This study researched several recommended NDE 

technologies that are capable of detecting and locating 

buried utilities. GPR remains the most reliable and 

consistent NDE method available for the buried-utility 

application. This study demonstrated the current state 

of the art in GPR technology (multifrequency GPR and 

stepped-frequency GPR) as an established and reliable 

method for utility location, especially for dry environments 

without clay present. FDEM was successful in surveys of 

metallic utilities and for obtaining depth of burial of the 

pipe and ground conductivity. This can include the presence 

of disturbed soil that can be indicative of buried pipe of 

any kind, including PVC. The project team recommends 

FDEM for detection of shallow metallic pipes, but the lack 

of a real-time display reduces its effectiveness for utility 

location. The application of the TDEM method is well 

demonstrated for the detection of metallic pipes as well, but 

it was not tested in this project (Sterling et al. 2009).

Seismic methods, such as MASW, proved to be a new 

emerging technology for NDE, given their success 

at locating buried utilities at one of the field sites in 

southern Virginia. Although MASW should not yet be 

considered as a standalone NDE technology for buried 

utility detection and location, it is the most promising 

non-GPR technology investigated in this project. Further 

investigation of best-practice acquisition strategies and 

improved data processing could place MASW well ahead 

of other NDE technologies, particularly for nonconductive 

pipe materials emplaced at depths below approximately 

4 ft. Seismic methods are not limited by moisture and 

soil type, which also makes them an attractive alternative 

method when GPR fails.

By conducting fundamental, comprehensive research of 

existing and emerging NDE technologies, this project 

successfully tested and identified various NDE technologies 

to detect and locate different types of buried utilities. Table 1

lists the various technologies, setup parameters, ideal testing 

conditions, and the researchers’ recommendations.

The researchers recommended the following next steps: 

• Perform further field evaluations for all NDE 

technologies across an extensive range of geological 

environments (e.g., high clay content, wet soil) and 

different utility types.

• Investigate MASW as a promising complementary 

NDE technique.

• Develop ensemble techniques to boost utility 

detection and location performance with existing 

sensor technologies.

Figure 4. Image. Two-dimensional shear-velocity profile (ft/s) with depth (ft) versus survey location (ft) 

at a field test site in Carrollton, VA.

Source: FHWA. (created using MASW ParkSEIS © version 1.01 (Park Seismic LLC. n.d.)).

Vs = shear velocity.
6

Table 1. NDE technologies setup, parameters, ideal test conditions, and recommendations for utility detection.

Method Technology Suggested Setup 

and Usage Parameters

Ideal Conditions Recommendations

GPR

Multifrequency 

impulse GPR

Steppedfrequency GPR

Use wide spectral band 

wherever possible. 

Prioritize low frequencies 

in the 100–400 MHz range.

Use operator-driven GPR 

for rugged and nonideal 

field conditions.

Use vehicle-mounted GPR 

under ideal conditions for 

high-speed data collection.

Homogeneous soil 

conditions with little 

to no clay.

Dry environments.

Relatively flat, firm, and 

even surface conditions 

for scanning.

GPR recommended 

for detection of buried 

utilities, particularly 

for metallic pipes.

Electromagnetic 

technologies

Pipe and cable 

locators

Cycle through frequency-detection 

modes on the locator to 

identify the most effective 

mode for a utility type.

Homogeneous soil 

conditions with 

little to no clay.

Dry environments.

Recommended 

for detecting active 

cables or where 

connection can be 

made to the buried 

utility to support 

the locator.

Passive location 

modes are not 

recommended 

for detecting 

unpowered utilities.

FDEM

Cycle through frequency-detection 

modes on the locator to 

identify the most effective 

mode for a utility type.

Homogeneous soil 

conditions with little 

to no clay.

Dry environments.

Relatively flat, 

firm, and even 

surface conditions 

for scanning.

Recommended for 

detection of shallow, 

metallic pipes. 

Lack of a real-time 

display reduces its 

effectiveness for 

utility location.

Acoustic 

technologies APL

Select 6-ft instrument spacing 

to ensure an effective 

density of data points.

Select deep-mode data 

collection to ensure instrument 

captures effective depth.

Homogeneous 

soil conditions with 

little to no clay

Dry environments.

Relatively flat, 

soft, and even 

surface conditions 

for scanning.

Inconclusive for 

utility detection.

Seismic 

technologies

MASW

Minimum of 24 geophones 

and a shoot-through 

approach recommended.

Source weight between 1.5 

and 4 lb for pipes < 15 ft.

Pipe depths 

from 3 to 12 ft.

Sensor locations on 

soil, grass, or asphalt.

Good impedance 

contrast between 

utility and soil.

MASW recommended 

for further testing 

with shoot-through 

acquisition geometry.

HVSR

Requires at least four broadband 

sensors at a minimum spacing 

equal to the pipe diameter.

General location of 

utilities must be known 

due to the time required 

to apply the technique 

(~30 min/site).

Inconclusive for 

utility detection.
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REFERENCES

Park Seismic LLC. n.d. MASW ParkSEIS (software). 

Version 1.01. 

Reiter, D., Napoli, V., Cohen, J., Boone, S., Moseley, P., 

Alhasan, A., & Salerno, J. (forthcoming). Availability, 

Feasibility, and Reliability of Available Nondestructive 

Evaluation (NDE) Technologies for Detecting and 

Locating Buried Utilities. Washington DC: Federal 

Highway Administration.

Sterling, R. L., Anspach, J., Allouche, E., Simicevic, 

J., Rogers, C. D., Weston, K. E., & Hayes, K. (2009). 

Encouraging innovation in locating and characterizing 

underground utilities. Washington DC: The National 

Academies Press. SHRP2 Transportation Research Board 

Report S2-R01-RW. doi:10.17226/22994.

Researchers—This study was conducted by the FHWA Office of Infrastructure Research and Development under 

Contract Number 693JJ320C000005 with Applied Research Associates, Inc. and Bridge Diagnostics, Inc.

Distribution—This summary report is being distributed according to a standard distribution. Direct distribution is 

being made to the FHWA divisions and Resource Center.

Availability—This TechBrief may be obtained at https://highways.dot.gov/research.

Key Words—Nondestructive evaluation, buried utility detection and location.

Notice—This document is disseminated under the sponsorship of the U.S. Department of Transportation (USDOT) 

in the interest of information exchange. The U.S. Government assumes no liability for the use of the information 

contained in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or 

manufacturers’ names appear in this TechBrief only because they are considered essential to the objective of 

the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides high-quality information 

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FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous 

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Recommended citation: Federal Highway Administration, 

Availability, Feasibility, and Reliability of Available 

Nondestructive Evaluation Technologies for Detecting 

and Locating Buried Utilities (Washington, DC: 2022) 

NOVEMBER 2022 https://doi.org/10.21949/1521921. FHWA-HRT-22-111 

HRDI-30/11-22(WEB)E