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Saturation Plumes (GPR)

The Problem:

A client in central Alberta had a number of buried pipeline systems. These systems ranged from fresh water to processed product. They were all buried under the same concrete pad. The drawings of the site very accurately showed the locations of these pipes and the system worked well for many years. Unfortunately, systems age. Buried pipes are not immune to wear and tear. During routine testing, cross contamination was found from one line to another, and a saturation plume of unknown extent was suspected. It appeared that beneath this portion of the concrete slab two lines were leaking, allowing product to flow into the ground, mix, and flow back into the leaking pipes. Obviously, repairs were in order, but these pipes ran together underground for hundreds of meters, and localizing the source of the problem using conventional means would involve costly and destructive removal of soil along the entire pipeline system.

The Solution:

There are technologies more ideally suited to contamination plume mapping (such as electromagnetic profiling or resistivity), however due to the steel-reinforced concrete and surrounding structures, these other methods could not be deployed.

Ground Penetrating Radar (GPR) was performed on the concrete pad without digging and without disturbing the pipes in any way. Data was gathered and analyzed back in our office. A pattern emerged where the saturation below ground showed a definite and repeating pattern on consecutive lines of GPR data, allowing us to locate a small area in which the subsurface was overloaded with moisture. This allowed the client to narrow the search area to just a few meters of pipeline. As an added benefit, the probable extent of the contamination plume was determined. This greatly aided the assessment of the environmental impact. A broader scan of the entire unit demonstrated that there were likely no other similar subsurface problems.

Saturation

The Results:

Despite the limitations of GPR for saturation and plume mapping, Maverick technicians were able to provide the required results. Maverick Inspection Ltd. then used a remote camera system to explore this area of pipeline. It was determined that a hairline crack had formed at a junction, and as the water table rose and fell, fluids were able to flow into and out of this crack.

This scenario demonstrated that a capable technician can use remote sensing technology outside of conventional applications if needed. In addition, combining approaches such as GPR and video inspection provides a fuller picture than simply deploying a single system or method.

 

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