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How Does GPR (Ground Penetrating Radar) Work

Utility Survey — Wed, 16 May 2012 18:00:42 +0000

So, How does GPR work?

In layman’s terms, GPR works on the same principle as sonar or aerial radar (what the police use). A radar wave is pulsed into the substrate (ground, concrete, etc.) at a certain frequency. Then, over time and distance, an image can be produced based upon the reflection of what the wave bounced off of. Typically, this image is in the form of peaks and hyperbolas in the data collected. If the wave finds nothing to reflect off of, it will gradually dissipate as it passes through the material. How deep the GPR wave travels is largely dependent on the material/soil it is trying to pass through.

Reflections are also produced when the electric conductivity of the soil changes. This electric conductivity is known as the dielectric constant of the soil. Soil types that vary considerably with their dielectric constant show greater contrast then soil types that are closer in their dielectric number. The dielectric number is also a limiting factor in GPR penetration. Essentially, the higher the dielectric number, the lower the depth of penetration of the GPR wave.

I hope this helps the reader to get a basic understanding of how ground penetrating radar works (GPR). Please feel free to ask any questions in the comment section at the bottom of this post.

Choosing a Private Utility Locate Company

Utility Survey — Mon, 12 Mar 2012 15:51:32 +0000

It happens to almost every contractor at one time or another; he/she makes a call to the public one-call service, assuming that’s all they will need, and then seeing the majority of the one-call marks terminating at the edge of the property in question and not even entering the area of excavation. It’s obvious that the dig site hasn’t been thoroughly vetted for utilities. When the public service is called and questioned, the person on the other side of the phone politely says that their responsibility ends at the private property line. Now what does a contractor do? What does one look for when searching for a private utility locate company? Here are some suggestions:

The first thing to look for is whether the company has been around for an appreciable amount of time. The longer the better. Longevity suggests stability and that the company has been established as a leader in its industry. Talk to them; ask about their experience and ask for references from contractors they have done work for. Ask about large scale jobs that they may have done, then call the General Contractor for those jobs to get their opinion. Remember, reputation is everything.

Secondly, what equipment do they use? The advantage of a private locator is that they usually have more equipment choices to facilitate a better utility locate. A public one call locator usually will only have a single pipe locator to locate a single utility. A good private locator will usually have two or three pipe/cable locators, a ferro-magnetic locator, and certainly Ground Penetrating Radar (GPR) systems. GPR is a must in certain situations to locate targets that are non-metallic or non-conductive.

Finally, does the private locator demonstrate professionalism? Here are some things to look for: Do they answer the phone in a courteous manner? Do they return phone calls in a timely fashion? When questioned, do the technicians exhibit mastery of their equipment and inspire confidence in their abilities? Every contractor is owed a professional and courteous experience from the first phone call to the completion of the job.

A contractor in need of a private mark-out should expect an experienced and professional utility locate company with the latest pipe/cable locators in combination with good GPR systems to be brought to the job site. Utility Survey Corp. has been a leader in the private utility location industry for more than 20 years. We incorporate modern GPR systems for both concrete and terrain scanning as well as the latest pipe/cable Radio-Frequency based locators. Combined with a professional experience that our clients have come to trust, Utility Survey Corp. has cemented itself as the right choice for all private utility location needs. Proceed With Confidence and Call US before you dig!

Site Investigation and Problem Solving with Utility Location Services

Utility Survey — Thu, 08 Mar 2012 16:52:47 +0000

Problem solving doesn’t necessarily go hand-in-hand with the average utility location service. Utility locating can have more applications then just protecting utilities from damage. Often, utility location can be done for purely investigative purposes alone. It’s important for any private utility locating service to have good problem solving Technicians with the experience to know what approach, or combination of approaches, will yield the best results for a client.

Recently a client approached our company with extremely high electric bills. The electric meter was several hundred yards from the building. Part of the property was city parkland and the other part was a private enterprise. The client suspected that the city was tied into his electric service. Utility Survey was hired to locate the underground electric. Locating unaccounted for utilities can have tremendous cost savings. It was recommended that an additional electric sub-meter be installed at the building where the client could better monitor his electric consumption. Over time properties are subdivided and redeveloped and many times the existing underground utilities are not updated. An underground utility survey can often answer questions that go on for years in regards to utility consumption.

The history of a site will often require an investigative locate. Old drawings suggesting utilities that may or may not still exist can often require a varied approach to determine what is still current to the site. A Technician’s experience in site investigation with a keen mind for problem solving is an important factor for success on sites like these.

For over 20 years Utility Survey’s clients have relied on us to be their solution for various site investigations. It’s our experience combined with the latest equipment that gives us a decided advantage over many of our competitors. It’s an advantage that saves our clients time and money! Proceed with confidence; Call Utility Survey for your next site investigation.

Electromagnetic Induction (EM) and Environmental Site Investigation

Utility Survey — Tue, 21 Feb 2012 21:52:22 +0000

: 2000 Hz Inphase

One of the best uses for electromagnetic induction (EM) is Environmental site investigation. In this post, an environmental site investigation was requested on a former 1950′s era military facility. This site is now recreational fields for a local high school. The concern was the possibility of old underground storage tanks that may have been left behind and any pollution that could have leaked into the surrounding soils. The GSSI EMP-400 EM Profiler was employed for some of the data collection for this site.

The image to the left was a typical data image for the survey profiled at the 2000 Hz Inphase setting. Two areas specifically stand out within this image. First, in the area running from 20-30ft along the x-axis and continuing the full length of the y-axis, there’s a strong dotted pattern all along this area suggesting a concrete slab below the grassy turf. Second, the orange-red area at the 0 x-axis, 50 y-axis location in the image suggested a possible metal target (it was determined on site that this was a small pile of metallic debris).

This is just a small example of the usefulness an EM profile can produce. Large areas requiring an underground storage tank survey, septic tank/field investigation or differentiating soil conductivity for environmental assessment can be done efficiently and in a cost-effective manner. The EMP-400 can be incorporated with GPS to speed data collection and correlation with any area being surveyed. Any Phase 1 or 2 environmental assessment looking to establish some level of ground truth in a non-invasive manner, would benefit greatly from an EM profile depending on history and specific aspects of the investigation.

Using an EM profile is of great value for environmental assessment. The GSSI EMP-400 is a great tool for data collection to help facilitate that environmental assessment. Utility Survey Corp. employs the EMP-400 as well as the latest Ground Penetrating Radar systems to assure a high level of customer satisfaction.

Proceed with Confidence! Call US for effective environmental assessment data.

Environmental and Geological Assessments Using the GSSI EMP-400 Electromagnetic Profiler

Utility Survey — Wed, 15 Feb 2012 16:10:18 +0000

The Profiler EMP-400 is a frequency domain, electromagnetic profiling system. It’s an extremely flexible induction tool because it allows the operator to select multiple frequencies for surveying. By acquiring multiple frequencies, the user can select the frequencies that provide the best results for a specific application. Up to three frequencies can be selected in the range of 1,000 Hz to 16,000 Hz giving a broad spectrum of application within inphase, quadrature and conductivity modes of EM data.

By using the Profiler as a quick reconnaissance level survey tool, users are better apt to narrow down areas of interest on large survey sites for more invasive investigation such as potholing or borehole sampling. The Profiler can also be used hand-in-hand with other methods like Ground Penetrating Radar (GPR) to broaden the information gathering and to better the identification of subsurface anomalies or to differentiate structures.

Many companies find Electromagnetic Induction (EM) to be an effective survey method for large-scale environmental assessments, such as UST and drum locating, pollution plume mapping, septic field and landfill delineation.

Electromagnetic Induction is also a useful tool for geological assessments, as well. The EMP-400 Profiler can be used to establish the salinity of soils by measuring its conductivity. This can be used for agricultural and watershed examination. The establishment of salt-water infringement into fresh-water systems or conductive soil delineation from more mineral-based soil types.

Utility Survey Corp. employs the GSSI EMP-400 Profiler for the aforementioned disciplines and for many utility based industries, as well.

Proceed with confidence…, Contact Utility Survey Corp. for your assessment needs.

Is the Water Main Leaking?

Utility Survey — Tue, 31 Jan 2012 21:14:11 +0000

It’s a difficult thing to be a Town Water Supervisor under the stress of investigating a possible leak problem. Small to mid-sized water companies can be devastated by a single, large main break that refuses to show itself or a handful of small leaks adding up to big problems. This often leads to an “all-hands-on-deck-find-it-and-fix-it” type of panic mode. So when a wet spot is found or a pool of standing water is discovered, it’s all they can do to keep from firing up the back-hoe.

Often a Client’s basis for believing they have a leak problem is subjective and based upon environmental or physical cues (i.e. standing water along a pipe route or damp areas near a water main). While physical cues can be helpful, they are not, in and of themselves, necessarily true indicators of leakage. Listening for leak sound at sounding points, quantifying water loss and observing pressure issues are part of a foundational approach for leak location. These are just stepping stones toward more complex procedures but can prevent looking in the wrong direction and wasting time and money.

Determining for certain that leakage is the source of a system’s unaccounted for water loss is vital. Often for a small system, it’s obvious: people complaining about low pressure, pumps running all the time and a near empty water tower pretty much signal a major leak is at hand. However, for a larger system, a much more systematic approach is needed. What’s the unaccounted for water percentage? Are the meters reading accurately? Is there any metering lag or overlap within the book-keeping of the meter readings? These are just a few of the questions that need to be answered.

When definite leak issues are determined, proper sounding of hydrants, valves, service shut-offs and blow-offs in a methodical, systematic way is more beneficial than going specifically on physical cues. Pressure readings, zoned usage patterns in combination with physical cues can give a Leak Technician a good place to start. A whole systematic approach is necessary and needs to be a standard practice for every water system.

We at Utility Survey Corp. practice that systematic approach. This approach, when following through with leak noise correlation pinpointing of a leak, or leaks, achieves a high rate of success. Success that our Clients expect and depend upon. Call US for your leak detection needs.

Ground Penetrating Radar Antenna Selection and Techniques for Determining Concrete Slab Thickness

Utility Survey — Tue, 24 Jan 2012 17:50:42 +0000

Selecting the proper GPR antenna frequency is critical when scanning concrete. Resolution levels can make a difference between useful information to a client and inconclusive data. Utility Survey Technicians carry a range of antenna frequencies which can be switched in a couple of minutes. A good example of this would be determining concrete slab thickness.

Many of our clients assume the floor slabs are much thicker than they actually are. The Technician starts with a deeper penetrating GPR antenna with a lower resolution making it very difficult to distinguish between slab and material under slab. At this point the Technician switches to a higher resolution lower penetrating antenna. The result of this change is a clearer distinction between slab and material under slab. Once the proper GPR antenna is determined for the requested task one can usually continue with that for the rest of the job.

Another impediment to determining concrete slab thickness is the reinforcement within the slab. Too many reflectors within the slab limit the amount of radar wave that can penetrate and create enough resolution for the bottom of the slab to be seen. With most concrete imaging GPR systems, there wouldn’t be any recourse short of cutting or drilling in determining the bottom of the slab. However, Utility Survey uses Geophysical Survey Systems (GSSI) concrete GPR systems. Their radar systems allow a 90 degree orientation change of the antenna. This allows the metallic reflection of rebar and mesh to be muted enough where plastic conduit and the bottom of the slab to be more apparent. These are currently the only systems in the industry that allow for this change of orientation.

So if slab thickness and the location of plastic conduit is of interest to your project, select Utility Survey and the GSSI concrete systems for your next project.

The Concrete X Ray vs. Ground Penetrating Radar (GPR) Decision

Utility Survey — Tue, 16 Aug 2011 15:17:27 +0000

Concrete x ray vs. GPR

As a company that’s been in the utility locate industry for over 20 years, we’ve been asked a number of times whether we “do x-ray” or not. This usually starts a conversation with the prospective client about the differences and benefits of GPR vs. X-ray. While the benefits of x-ray technology can be immense, most of our clients will agree, that the ease of use, safety and lower cost of GPR makes it a much better choice for their needs; as detailed in the following.

GPR waves are much less harmful then x-ray and are controlled by FCC regulations due to them being in the radio bandwidth. They are roughly the same power level as cell phones. Concrete x-rays require high levels of PPE (Personal Protection Equipment) to keep the Technician safe and usually require an approximate 80 foot clearance area of any other people that may be working in the area. This often requires a shut down of other work or services that may be going on in the area.

GPR on concrete usually has the advantage of only needing one side of a concrete slab, while x-ray requires both sides of a slab; one for the film and the other side for the reflector plate. As a result, any slab on grade job can not be accomplished with concrete x-ray. GPR is not perfect in a slab on grade situation. If a slab is extraordinarily thick (18-inches or greater), a lower GPR frequency will have to be used resulting in a loss of resolution. However, slabs of such thickness are usually the exception rather than the rule.

One benefit that x-ray has over GPR is that, in most applications, x-ray does have higher resolution of targets within concrete. However, GPR has closed the gap with higher resolution frequencies as high as 2.6 GHz.

One final difference between the two technologies is cost. Concrete x-ray is much more costly to implement than GPR. And with advancements in software, GPR data is much more easy to process and cross various platforms.

As previously stated, x-ray can produce wonderful high resolution images that can be of great benefit. However, it is also an extremely costly technology that can be difficult to implement with success. With GPR, you have a much more inexpensive, user friendly option that provides quality data for the needs of municipalities and industry with much fewer limitations than x-ray. Whether locating conduit, rebar or various structures within and below concrete slab, contact US for all your location needs.

Essentials of a Good Utility Location Survey for Private Utility Locators

Utility Survey — Mon, 08 Aug 2011 18:30:29 +0000

A Good Private Utility Location Survey

There are many multi-step methods advocated by public one-call companies and experts, and they are all good and useful and can push a “newbie” locating professional in the right direction. But public locators often have one thing that the private locators don’t have access to…,records! When you are a private utility locator, there are often no plans to work with, records, microfiche or even opinions to where all the hidden dangers might be.

So here’s a few suggestions for that next private utility survey that you have just been hired to do.

A visual walk through of the site is a critical first step in a underground utility survey. Topographical awareness can be very beneficial to a locate on a site with little information. Look for settling under asphalt or in grassy areas running at length. Long, longitudinal cracking in asphalt can be a sign as well as runs of dried grass or grass that is a slightly different color. These physical clues can be of great help on any job site.

Don’t overlook the obvious. Manhole covers are often mislabeled. Always open to confirm. Ask for access to utility rooms and basements where utilities enter buildings. Try to determine material composition of the utility you are trying to locate (metal, plastic, etc) and come up with the best way to locate each individual underground utility in your mind before you begin. A few minutes spent on a visual walk through can save a lot of time and confusion later in the survey.

Listen with intent. Asking good questions can be critical to success. When on site with a client, be sure to ask about history of the site or if there is anyone there with prior knowledge. When receiving that knowledge, always remember that over time memories can fade a little and physical landmarks can change. So, listen with the intent of gleaning information of what may be there but not to use that information as an absolute for location purposes.

Locating Pipes, Conduits and Multiple Targets within AND below Concrete Slab

Utility Survey — Mon, 25 Jul 2011 17:12:05 +0000

Is it possible to locate pipes, conduits, and other hidden targets, not only inside…, but also underneath concrete slabs?

Hidden targets such as electric conduits situated inside concrete slab pose problems of a potentially dangerous nature before a client begins saw-cutting or coring. Just imagine

when you have utilities both inside and below the slab to worry about.

Whether it’s a conduit located below or tied close to a rebar rod, or a floor drain underneath a slab (and at what depth?) or knowing what the slab thickness is to adjust a concrete saw to, the need for a full frequency range of Ground Penetrating Radar (GPR) antennas that can resolve these issues is a must.

What’s needed is a GPR system with a complete range of very high frequency antennas to “see” objects and conduits within slabs of varying thickness AND to see targets at the underside and below a slab.

There is no universal “see all” GPR antenna to cover all applications. Utility Survey deploys GPR systems with a full complement of antennas operating on different frequencies to give our clients the best information possible so they may complete their work safely and cost effectively.

GPR isn’t entirely infallible however, and it can have limitations under certain conditions. But, for the vast majority of needs, it is THE only accurate, safe, and cost effective concrete scanning solution.

Need more information? So scroll up to the top of the page and click on the “Contact Us” button. We would be happy to answer any question you might have to determine if Ground Penetrating Radar is the right solution for your company’s needs.