Before any excavation, accurate underground utility locating is essential to prevent utility strikes, project delays, costly repairs, and safety hazards. In modern construction, infrastructure development, and utility installation projects, two primary technologies are used for subsurface utility detection:
Understanding when to use each method—or combine them—is key to safe excavation planning, utility damage prevention, and compliance with industry safety standards.
According to OSHA’s Trenching and Excavation Safety guidance, contractors must identify underground installations before digging to reduce the risk of injuries, fatalities, and infrastructure damage. The CDC National Institute for Occupational Safety and Health (NIOSH) also emphasizes hazard prevention and engineering controls in construction environments where underground utilities may be present.
For projects involving unknown underground infrastructure, many contractors combine utility locating, underground utility location, and utility verification services to obtain a more complete understanding of subsurface conditions before excavation begins.
Ground Penetrating Radar (GPR) is an advanced, non-destructive utility locating method that uses high-frequency radio waves to detect underground objects and changes in subsurface material density.
GPR sends electromagnetic pulses into the ground. When those signals encounter a change in material—such as soil, concrete, plastic, metal, or void spaces—they reflect back to a receiver. These reflections are processed into visual data that helps technicians identify underground infrastructure.
According to the Federal Highway Administration’s Subsurface Utility Engineering program, GPR is an important tool for reducing utility conflicts and improving project planning.
GPR can identify:
Because it does not require a direct connection to a utility line, GPR is particularly effective for locating infrastructure that may not appear on utility maps.
This makes GPR a valuable complement to Adler’s Utility Mapping Solutions and Utility Verification Services when working in congested or poorly documented utility corridors.
Like all locating technologies, GPR performs best under certain conditions.
The USDA Web Soil Survey and the U.S. Geological Survey provide valuable information about local soil conditions that may affect GPR performance.
Electromagnetic locating is a traditional utility locating method used to identify conductive underground infrastructure.
EM locators transmit an electrical signal through a conductive utility or trace an existing signal. A receiver then follows the signal path from the surface to identify utility locations.
EM locating is often paired with underground utility location and hydro excavation to improve utility verification and reduce excavation risk.
The most reliable underground utility detection strategy is not choosing one technology—it is combining both.
The Federal Highway Administration recognizes GPR as a complementary technology rather than a standalone solution in utility engineering workflows.
This approach aligns with industry best practices promoted by the American Public Works Association and the Common Ground Alliance, both of which advocate for comprehensive damage-prevention programs.
Excavation safety begins before the first shovel enters the ground.
Contractors should always contact the national Call Before You Dig system before excavation:
However, 811 only marks public utilities. Private utilities—including private electrical lines, communication systems, irrigation infrastructure, and facility-owned pipelines—typically remain unmarked.
This is why GPR, EM locating, and daylighting with hydro vac are often necessary to achieve complete site coverage.
Using only one locating technology can increase the risk of:
According to OSHA and NIOSH research, failure to properly identify underground hazards remains a major cause of excavation incidents.
Accurate utility locating is essential for safe, efficient excavation. While EM locating is highly effective for tracing known metallic utilities, GPR provides critical visibility into non-metallic and undocumented infrastructure. Together, these technologies offer the most reliable approach to reducing utility strikes, project delays, and safety risks.
Before your next excavation project, trust Adler Hydro Vac for professional utility locating, GPR scanning, utility mapping, and verification services. Contact Adler to help ensure your site is accurately mapped and excavation-ready.
GPR should be used when non-metallic, undocumented, or difficult-to-trace utilities may be present. Unlike EM locating, GPR can detect PVC pipes, fiber optic lines, HDPE conduits, concrete-encased utilities, and other subsurface features that do not conduct electricity.
Using both technologies provides the most complete understanding of underground conditions. EM locating accurately traces metallic utilities, while GPR helps identify non-metallic and unknown infrastructure, reducing the likelihood of missed utilities and excavation-related incidents.
No. The 811 system generally marks publicly owned utilities only. Private utilities—including facility-owned electrical lines, communication systems, irrigation infrastructure, and private pipelines—may remain unmarked and require additional locating services such as GPR and EM scanning.
Comprehensive utility locating helps identify underground hazards before excavation begins, reducing the risk of utility strikes, service interruptions, costly repairs, project delays, worker injuries, and regulatory violations. Proper utility detection is a critical component of safe excavation planning and risk management.
