Frequently Asked Questions

Ground Penetrating Radar

Ground penetrating radar is a type of technology that uses radar pulses to create images underground. It is also known as GPR, ground radar, subsurface scanning, georadar or ground probing radar. Radar is used for utility locating and archaeology purposes too. It can penetrate up to 100 feet depending on the antenna used. A typical utility application configuration will go to a depth of 10 – 15 ft deep in scanning depending on the soil type and moisture level. Radar can be highly accurate at location, while identifying underground objects requires experience and skill.

GPR works by sending a tiny pulse of energy into a material and recording the strength and the time required for the return of any reflected signal. A series of pulses over a single area make up what is called a scan. Reflections are produced whenever the energy pulse enters into a material with different electrical conduction properties or dielectric permittivity from the material it left. The strength, or amplitude, of the reflection is determined by the contrast in the dielectric constants and conductivities of the two materials. This means that a pulse which moves from dry sand (dielectric of 5) to wet sand (dielectric of 30) will produce a very strong reflection, while moving from dry sand (5) to limestone (7) will produce a relatively weak reflection.

While some of the GPR energy pulse is reflected back to the antenna, energy also keeps traveling through the material until it either dissipates (attenuates) or the GPR control unit has closed its time window. The rate of signal attenuation varies widely and is dependent on the properties of the material through which the pulse is passing.

A Ground Penetrating Radar can be used in freshwater. However, it cannot be used in places where salt water is present. It can also be used in snow and ice. Depending on the site conditions high levels of moisture can have a negative impact on our ability to provide accurate locate data.

Irrigation main lines often have wires and can be easily located by wires. However irrigation lateral lines require more in depth locating. Typically it is not cost effective to locate vs the cost to repair them if they are hit (i.e. 50 cent pipe fitting vs locate cost).

Many people wonder whether it is safe to use GPR equipment. The answer to that question is yes. Ground Penetrating Radar may sound dangerous, but it is actually a safe technique. In fact, the radar only emits about one percent of the power that the average cell phone emits.

Ground Penetrating Radar itself does not identify utilities. It is the operator and their interpretation of the data presented that can identify potential anomalies in the ground. Based on additional information about the site, we can draw conclusions as to what is underground.

Members of our trained team are able to identify the type of utility by tracing it using Utility Locate Equipment other than GPR.  They are also able to identify features, such as control boxes, valves and meters. However, if the locators are not able to direct connect to the specific utility they may not be able to conclusively identify it.

GPR in general is used to scan subsurface anomalies. First, our team can determine what is normal in a specific area, then our team can then determine what is not normal. Abnormal areas are referred to as anomalies. Depending on the scope of the job, these anomalies could be anything from unknown graves to tunnels. They may also be environmental hazards such as buried tanks or explosives.

General Questions

WOOD Inspection Services is dedicated to subsurface locating both for private utility projects and concrete scanning. We pride ourselves on being focused on the customer. We provide as much possible information as we can to our clients. With decades of experience on a variety of job sites and applications (empty voids and sink holes to concrete structures), we use our skill and the latest technology to reveal underground. We will be honest about what services you need. Even if that means we don’t provide the services.

While it is very easy to purchase GPR equipment online, it is far more difficult to use and interpret results. That is why hiring a company with experience and training makes a large difference in GPR results. Training typically consists of an equipment certification, hands-on instruction and in-the-field experience. WOOD Inspection Services has decades of experience with GPR and other technologies to help clients find their answers.

Yes, Wood Inspection Services is available for weekend and emergency on site inspections at an extra cost. The fees vary based on the service required. Contact us with any questions about work outside our regular working hours.

GPR equipment transmits and receives electromagnetic energy. That is why it is a good idea to turn off cell phones, pagers and two-way radios should not be used around a GPR. The electromagnetic radiation can interfere with the ground penetration radar signal. If one has to use these devices, then they should be kept at least 10 feet away from the GPR equipment.

Hiring GPR Contractors vs Alternatives

Metal detection is limited to metal only, while GPR locates targets by identifying anomalies in the soil. For example, it can such reveal different soil densities of an area that has been dug up next to an area of undisturbed soil. This also allows GPR to identify targets that do not contain metal, including empty space, PVC utility piping and unmarked graves.

Metal detectors and GPR are completely different technologies. Also, metal detection has depth limitations which makes it insufficient for commercial inspections, while GPR can reveal obstructions up to 100 feet underground.

A structural engineer would be hired when there is a requirement to render an opinion regarding a repair, design or failure.  We do not ever try or intend to replace the need of a structural/foundation engineer. However we often complement or add valuable information for engineers to render their opinions. (ie. provide location or spacing of rebar or grade beams). For this reason, we are often hired by foundation contractors and engineering firms.

Soil tests are completed to determine soil composition. Based on soil tests, a structural engineer would specify different types of design for foundations or buildings. It can also be used to check for soil contaminants. Soil tests are performed by drilling and taking soil samples. WOOD Inspection can be hired to confirm that no utilities or other obstructions are hit during the drilling process.

Land surveyors are hired to map out boundaries, elevations, buildings, or other visible landmarks on a property. They do not and cannot document items they do not see or that are underground. Oftentimes we are called in prior to the surveyor’s work, to provide utility locating services so they can include utilities and other underground targets in their survey.

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