Twin City Locating, LLC
Private Utility Locating and GPR (Ground Penetrating Radar) services
(360)720-3333
GPR Utility Locating Services
Ground penetrating radar, also called GPR, is used to help reduce or eliminate the risk of damaging an underground utility. GPR is used to help identify underground utilities and buried subsurface features when standard signal based electromagnetic locating is limited or not enough by itself. Twin City Locating provides GPR utility locating for homeowners, contractors, property owners, and various customers in Southwest Washington and throughout the state for those who need a better idea of what may be underground before digging begins.
GPR is especially useful when buried utilities may be non-conductive, difficult to trace, poorly documented, abandoned, or located in a work area with multiple underground features. If a property has private utilities, unknown line routes, limited access points, or a more complicated underground layout, GPR can help provide a clearer picture before excavation, trenching, utility repair, fence installation, drainage work, or construction starts.
Twin City Locating provides GPR locating throughout Southwest Washington, including Lewis County, Thurston County, Grays Harbor County, Mason County, Pacific County, and Cowlitz County. If you are trying to decide whether GPR or another method is the better fit, this page explains where GPR works well, where it has limits, and how it fits into private utility locating on real properties.
What GPR Locating Is
A simple way to think about GPR is that it works somewhat like radar used in the air, but instead of sending signals through the sky, it sends signals into the ground. The GPR unit has an antenna that sends short pulses of energy downward into the soil, gravel, concrete, asphalt, or other surface being scanned. When those signals hit something different underground, part of the signal bounces back to the antenna.
GPR does not show a perfect picture of a pipe like an X-ray. Instead, it shows patterns, reflections, and changes in the ground. Utilities often appear as curved shapes, commonly called “hyperbolas,” on the screen as the antenna passes over them perpendicular to the underground path. By scanning in multiple directions and following those patterns, the operator can mark the likely path of a buried utility on the ground.
GPR is especially useful when a utility cannot be located with standard electromagnetic locating methods. Many private utilities are made of plastic, PVC, concrete, clay, or other non-metallic materials that do not carry a signal well. Examples may include plastic water lines, PVC sewer laterals, irrigation lines, drainage pipes, and unknown private utilities that were installed without accurate records. In some cases, GPR may detect the utility itself. In other cases, it may help identify the trench, disturbed soil, or other signs that indicate where the utility was installed.
A thorough private utility locate often combines GPR with other locating methods, including electromagnetic locating, sewer camera and sonde locating, magnetic locating, visible site features, utility records, and field experience. When used properly, GPR can greatly reduce uncertainty before digging and help homeowners, contractors, and property owners make safer, better-informed decisions.
Like any locating method, GPR has limitations. Results can be affected by soil type, moisture, clay content, depth, surface conditions, and the size of the buried utility. Wet or highly conductive soils as well as thick tall grass/plants can reduce how deep the radar signal can travel, while small or very deep utilities may be harder to identify. Because of this, GPR is best viewed as an advanced detection tool rather than a guarantee that every buried utility will be found.
Unlike electromagnetic locating, GPR does not depend on the utility being conductive or having tracer wire. That makes it one of the most useful options when a buried utility may be made of plastic, PVC, or another non-metallic material, or when the utility route is uncertain and there is no reliable traceable access point.​​​​​​​​​​​​
When GPR Is Often the Better Choice
When Utilities May Be Non-Conductive
GPR is often the better choice when the buried utility may be plastic, PVC, clay, or another non-metallic material that is difficult or impossible to trace with electromagnetic locating alone.
When the Utility Route Is Unknown
Some jobs start with a simple problem: the property owner knows a line exists, but does not know exactly where it runs. GPR is useful when the route is uncertain and there is not a good access point for tracing the line with standard methods.
When the Work Area Has More Than One Buried Feature
On some properties, the concern is not just one known utility. The work area may also include other buried lines, old improvements, abandoned utilities, subsurface changes, or structural features that matter before digging starts. GPR can help when the goal is to better understand the work area as a whole.
When Standard Signal-Based Locating Has Limits
Electromagnetic locating is extremely useful when a buried line is conductive and traceable, but it has limits. If a line does not carry signal well, cannot be directly accessed, or may not be conductive at all, GPR is often the more useful method to review.
What GPR Can Help Locate
GPR can be useful for locating or evaluating non-metallic utilities, unknown buried lines, sewer laterals, underground obstructions, buried structures, utility crossings, and congested underground environments where more than one buried feature may be present.
It is often used when the question is whether a private water line, sewer lateral, drain line, underground utility path, or other buried feature may be present in the work zone before excavation begins. Using ground penetrating radar will help or eliminate the risk of damaging an unknown or private utility.
Depending on the site, GPR may also help identify subsurface changes that matter for a project, especially where the concern is broader than just tracing one conductive utility.
GPR is a tool, designed to be operated by an experienced locator such as Twin City Locating. Where I offer nearly 20 years experience throughout Washington locating public and private utilities. More information about me can be found on my about page, and I will always be honest with homeowners and contractors about GPR and its limitations. As stated, GPR is a tool, to aid in the finding of buried utilities, but cannot always guarantee finding everything. This can be for a variety of reasons such as tree roots, age of the utility, and recent digging. If anyone claims they can, with certainty (especially before seeing the site in person), find all things and everything with GPR, they are not being honest with you.
Properties Where GPR Is Commonly Useful
Older Properties With Unclear Utility History
Older homes and properties often have buried utilities that were repaired, rerouted, extended, or added onto over time. When the current owner does not have a reliable map of what is underground, GPR can help where standard tracing alone may not answer the question.
Properties With Multiple Improvements
A property with a house, detached garage, shop, irrigation, drainage work, utility extensions, or older buried services can create a more complicated underground picture. GPR is often useful when the work area may contain more than one buried feature.
Properties With Limited Access Points
Some jobs do not have a clean place to connect or induce signal onto a buried line. In those situations, GPR becomes more useful because it does not rely on a conductive path in the same way electromagnetic locating does.
Properties With Planned Excavation or Trenching
When a project involves excavation, trenching, posts, drainage work, utility replacement, or construction in a specific work zone, GPR can help provide more information about what may be below the surface before work starts.
GPR and Electromagnetic Locating Often Work Best Together
GPR and electromagnetic locating are not competing services so much as different tools for different underground conditions. Electromagnetic locating is often the strongest choice when a buried utility is conductive and traceable. GPR is often the stronger choice when the utility may be non-conductive, unclear, untraceable, or part of a more complicated work area.
On many jobs, the best result comes from using both approaches together. Electromagnetic locating can help trace known conductive lines, while GPR helps evaluate what else may be present where signal-based locating has limits.
If you want a better explanation of signal-based tracing through electromagnetic locating, view more on electromagnetic locating for traceable conductive utilities. You can compare the two methods to see if that would work, or if you need the added function of ground penetrating radar.
If you still have questions or concerns, or how locating might work for your needs, you can reach out to Trent by phone via call or text.
What Affects GPR Results
GPR results can be affected by soil conditions, moisture, subsurface congestion, surface conditions, and the kind of buried feature being searched for. Not every buried object reflects radar the same way, and not every site gives the same level of clarity.
That is one reason GPR is best treated as a professional locating method that depends on site conditions, operator experience, and the specific question being asked. It can provide extremely useful information, but the property itself plays a big role in how clearly subsurface conditions can be interpreted.
If the ground is rough, unstable, heavily obstructed, or otherwise difficult to scan, that can also affect how useful the method is in a given work area as well as the time required to rule out false positives. Terrain can turn a 2 hour job into a 4 hour job, especially tall grass or weeds (when thick and/or 12" in height).
GPR results can be affected by soil conditions, moisture, subsurface congestion, surface conditions, and the kind of buried feature being searched for. Not every buried object reflects radar the same way, and not every site gives the same level of clarity. This is one reason why a GPR locate site can range from 2 hours to 6 hours for extreme conditions.
That is one reason GPR is best treated as a professional locating method that depends on site conditions, operator experience, and the specific question being asked. It can provide extremely useful information, but the property itself plays a big role in how clearly subsurface conditions can be interpreted.
If the ground is rough, unstable, heavily obstructed, or otherwise difficult to scan, that can also affect how useful the method is in a given work area.
GPR Service Area
Twin City Locating provides GPR locating throughout Southwest Washington, including Lewis County, Thurston County, Grays Harbor County, Mason County, Pacific County, and Cowlitz County. Our services are available statewide, though would take place on a Friday or Saturday. You can find more information about our service area.
What Helps Before Scheduling GPR
The most helpful information to send is the property address, the kind of project being planned, where on the property digging or work will happen, and what type of buried utility or unknown feature you are trying to identify.
That could involve a sewer lateral, private water line, underground power route, drain line, unknown buried utility, or a broader need to understand what may be in the work zone before excavation begins.
If you are still deciding whether GPR is the right fit, check out the Services page here. For additional tips or practices regarding both locating and safe excavation, our Best Practices would be worth checking.
If you are ready to continue, either call Trent to book an appointment, or do so here on our Booking Page.
Book GPR Locating
If you need GPR utility locating in Southwest Washington, use this page to decide whether GPR is the right fit for the project, then move to the Book Online page to request service.
If the project may involve non-conductive utilities, unknown underground features, or a work area where standard tracing alone may not be enough, GPR may be the best place to start.