Underground Location Experts

Public - Private - Everything

For over 15 years GPR OneCall has been a tristate leader in locating ALL types of buried underground utilities and structures. Using an arsenal of the industries most advanced locating equipment along with state of the art techniques, training and experience; we locate underground utilities that others might over look. Unlike an 811 mark out that only include public service utilities, we locate everything underground; from sewer lines to steam and everything in between, rest assured knowing you are covered.

We specialize in detailing ALL underground utilities at a site, no matter the complexity, and delivering the information on site with paint, flags, and to you in the form of detailed reports and maps.

In addition to conventional locating practices, our experience has helped us develop industry unique procedures and techniques that give us the confidence to know everything that is underground.

Our Utility Locating Services Include:


Full Site Locate and Mapping

We locate ALL utilities within a specific area and provide you with all the comprehensive information on what was discovered and marked. Unlike 811 services which only designate public utilities, we locate and verify the location of all utility services within the client provided scope of work, public and private. On site we indicate utility location clearly and effectively using paint and flags with our APWA based color index and provide a detailed field report with picture references, additionally, we can provide visually referenced utility field maps and map grade GPS obtained KMZ files. Please see below on our deliverables section for more specific information on our deliverables.

Boring and Excavation Clearing

Often in environmental testing or in construction projects only a specific area needs to be cleared of utilities for drilling, boring, excavation, or trench work. In this situation we can save time and money by detailing the underground utilities within a proximity to the work being performed instead of locating the entire site. Using our equipment and various passive scanning methods we can approve these areas as safe, indicate nearby utilities, indicate the presence of a conflict, and help devise a safe alternative location for unsafe proposed locations. If certain areas can’t be avoided, such as when trenching, then we can provide the most accurate depth and location information on the intersecting utilities.

Specific Utility Investigation

Sometimes only one utility, set of utilities, underground system or structure needs to be located for informational purposes. We can easily differentiate these utilities from others and deliver comprehensive underground information using our noninvasive processes in a quick and efficient manner.

Lost Utility or Structure Discovery

Sometimes things get buried or lost and we can find them! Whether buried by man or simply lost by the passage of time we can find utilities or other large buried structures. Valves, manholes, septic tanks, bunkers, time capsules, and even graves have all been relocated and cataloged thanks to our assistance.

More Than Just GPR

Ground penetrating radar is one of our most important tools but in delivering the most thorough possible results we utilize numerous other subsurface technologies and locating techniques at every job site to get the most comprehensive results.

Ground Penetrating Radar (GPR)

GPR is a technology that utilizes high frequency radio wave pulses to collect visual data on the subsurface below. We utilize GPR to help us locate and verify utility locations and depths along with our other locating methods, we specialize in using GPR to locate nonconductive utilities and buried structures. Nonconductive utilities and substructures include utilities such as empty plastic conduits, fiber optic cables, plastic gas lines, plastic water lines, concrete or plastic drain lines or buried non conductive structures, these types of utilities and structures are very difficult to locate or cannot be located with any locating method besides with GPR.

Electromagnetic (EM) Active Locating

EM active locating is a method which utilizes specifically tuned radio frequencies to induce and trace any conductive utilities. Utilities metal gas lines, gas line trace wires, electrical cables, metal sewer lines, metal water lines, and telephone lines are just a few examples of what can be traced and located using this method.

Electromagnetic (EM) Passive Locating

In addition to actively locating utilities our EM equipment has passive scanning capabilities that can locate 60Hz power frequency as well as a range of other frequencies that emanate from utilities. This method can be used to locate some utilities without being directly hooked onto them. Although this method is less reliable and less accurate than using GPR or EM active locating it helps us locate utilities where there is no above ground connection or indication of a utility presence.

Concrete Scanning

A concrete scanner is a small GPR specifically tuned to accurately locate utilities and reinforcing within a concrete slab. Although we categorize concrete scanning as a separate service from our utility locating, it is often used in tandem with our utility locating practices when doing a utility investigation inside a building.

For more information on our concrete scanning, please click the link.

Duct Rod Tracing and Sond Locating

Along with EM active locating there is duct rod tracing. When there is direct access to a nonconductive and otherwise untraceable pipe we can use a duct rod inserted into the pipe to trace and locate it with EM active locating. This is especially useful for locating empty conduits or conduits with untraceable utilities in them such as fiberoptic cables. We have various duct rod size and configuration as well as sond attachments to meet any job requirements.

Push Camera and CCTV Video Inspection

Our push camera and CCTV camera crawler equipment allows us to visually inspect the inside of various size and type of pipes. In doing so the pipe location and can also be accurately obtained. This is a separate service from our standard utility locating but it can be utilized in addition to our utility locating service for more comprehensive information on a specific utility.

Please click on the link for more information on this service.

Ferromagnetic Metal Detection

We utilize multiple metal detector types to find everything from underground storage tanks to small, buried utility valve covers.


Our most important tool and the most under-utilized tool in the entire industry is experience! To be proficient at using each of these methods and understanding how to effectively use them together to verify results and discover information that would otherwise be unattainable is the key. All our technicians are veteran locators and know how to use our equipment to its highest potential, in tandem with our own tried and true industry techniques nothing will be over looked at your site.

Types of Utilities Located:
All of Them

At a job site we use a combination of paint markings and flags to indicate the type of utilities located underground at the work site. The colors and symbols we use are based on the APWA Uniform Color Code for utilities and adjusted to fit a broader spectrum of utility types than what is referenced in this standard Color Code.


Whether it’s high voltage transmission lines or low voltage control lines we can easily locate all types of electric utilities with multiple of our locating techniques.


Water lines can include everything from a domestic service from a well to large fire supply loops supplying the hydrants and fire suppression systems on a property. Typically, water lines are energized from an accessible contact point like a hydrant and EM traced. Water lines cannot always be located with GPR due to their depth and depending on the substrate they are buried in, another reason why we employ multiple locating techniques.

Natural Gas, Petroleum, Fuel Oil, and Other Combustible Gases

Steel gas lines can easily be traced when they are made of steel and larger diameter gas lines can be located with GPR, small diameter plastic gas lines need to be EM traced using the trace wire located at the meter or a valve.

Steam and Condensate

although technically another gas, we differentiate steam lines from other gaseous utilities so more detailed information is presented through our markings at a site. Steam and condensate lines are almost exclusively metal and can be EM traced and located. Due to their large diameter sometimes these utilities can be located with GPR, depending on their depth and the substrate material around them.

Oxygen, Nitrogen, and Other Specialty Gas or Compressed Liquid Lines

These types of specialty gas lines are typically located at hospitals or medical manufacturing facilities, both of which are sites we have a lot of experience with. Typically these lines are copper and small diameter so they can be easily EM traced once accessed but very rarely located with GPR, depending on their diameter and depth.

Communication Lines

Telephone, Cat 5, Coaxial and Cable are just a few of the types of communications lines that can be traced and located with many of our locating methods. Fiber lines, which are made of glass, can typically only be located with GPR, when a trace wire or other conductive source is located in the conduit with the fiber lines or when we can access the conduit directly to insert and trace a duct rod.


Depending on their material and depth, which range widely from job site to job site, sewer lines are located using a variety of our methods; from opening a cleanout and tracing a PVC sewer line with duct rod tracing, to Actively EM tracing a cast iron sewer line, to verifying the location of either sewer line types with GPR.


Storm system lines are typically comprised of concrete or plastic and can’t typically be EM traced. Storm lines are located by accessing manholes and drainage grates and visually referencing the direction of travel to another point of access, the location is then verified with GPR and by visual verifying the same storm line at the next visual access points.

Unknown Potential Utility

Sometimes EM passive scans or GPR scans indicate the presence of a utility but no other information is present to indicate what type of utility it is. We locate and mark these potential utilities but sometimes they end abruptly in our investigation, they go into inaccessible areas or they travel far beyond the scope of work before connecting to any above ground indication. Often, we can inference what type of utility it is based on the types of passive signals we come across, the estimated depth or their size based on GPR images but without visual confirmation or direct access we mark them as unknown (UNK) potential utilities in pink on site. All the attainable information on the unknown utility will be presented in our deliverables to help you decide regarding it.

Our Deliverables

Information is only useful if its conveyed properly, that is why we have a variety of delivery methods; so you can access the information in a clear and concise way, exactly how you need it.

Field Markout

First and foremost, every job will be marked out on site based on our color code. We use a water based paint to make our marks at a site, this paint is semi permanent but will disappear over time, it will last longer on pavement, rock and other solid surfaces than it will on dirt or grass. Dirt and grass areas are also flagged according to our color code to help distinguish a markout for longer due to the physical impermanence of these surfaces. We understand that in some circumstances less is more and we are adaptable with what we use to mark in certain locations, for example; The nice granite tile entrance for a corporate building should not be marked with paint, in which case we can use more temporary mediums such as sidewalk chalk. Whichever medium is used for distinguishing utilities on site, all markouts are temporary to some degree which is why the proceeding post markout deliverables are so important.

Field Service Report

Every job comes with a field report. Our field reports are written detailed accounts of the job findings and include information such as the technician who performed the work, the time on site, the type of utilities located, depth estimates, which of our methods were utilized, any obstructions or limitations to the investigation, and any other outstanding or important information our technician discovered during their investigation.

Field Pictures

We take lots of pictures on site once or work is complete. Pictures document our work and provide you with a frame of reference without needing to be at the site, they are also useful for referencing markout locations years later, potentially after the markout has disappeared. We aim to take pictures that convey a lot of information and with permanent landscape features in relation to our utility marks so they can easily be referenced. Pictures are sent with every field report via email in the form of an easily accessible drop box link, where they can be viewed and downloaded.

Field Utility Map

In addition to our standard deliverables a field map can be completed to further document the work performed at a site. A field map is a satellite view of the job site overlaid with a visual illustration of the utilities located and other important information related to the job; A field service report and visual reference to the onsite markout in one easy to understand package.

KMZ and KML GPS Survey

All of our techs have a basic geo-satelite receiving unit and upon your request we can perform a basic (non-survey grade) satellite survey of the utilities located and include this information in the form of KMZ and KML file types.

According to the Common Ground Alliance Dirt Report for 2020 there were 385,381 utility incidents that resulted in $279.3 M in damages, 486 injuries and 8 deaths. While the largest percentage of why the incidents occurred was due to no mark-out request being made, 10.57 percent were caused by mis-marks and non-marks provided by the free public 811 services. A comprehensive, full utility investigation by technicians who are proficient and experienced in locating both private and public utilities provide a superior level of mark-out location and verification that will save you time, money and keep your workers safe.