Pyramid Geophysical Services has performed a multitude of Underground Storage Tank (UST) investigations throughout North Carolina using geophysical methods. These metallic USTs are often left behind at old fuel service stations that have closed down. Old home heating oil tanks are also often left in the ground after residences have converted to other energy sources. Both types of tanks can result in environmental concerns, and their locations are often unknown. A large number of the UST investigations that Pyramid has performed have been associated with road construction and improvement projects for the North Carolina Department of Transportation (NCDOT) Geo-environmental Division.
Pyramid typically implements two geophysical methods in a metallic UST investigation. First, a metal detection survey is performed using a Geonics EM61-MK2 electromagnetic induction metal detector. A contour map of the metallic anomalies is generated and overlain in Google Earth to observe their locations. Second, any anomalies that are suspected to be USTs are further investigated by Ground Penetrating Radar (GPR). Pyramid typically employs a GSSI SIR4000 control unit coupled to a 350 MHz antenna. The radar survey will delineate the approximate width, length, and depth of a possible metallic UST, or confirm that the anomaly is caused by some other object.
The figures below show an example of a project site associated with an NCDOT improvement project in North Carolina. The EM survey recorded multiple metallic anomalies that were associated with unknown objects in the subsurface. GPR surveys across these areas identified a total of 4 probable metallic USTs at the property. GPR scans across the width of a UST typically record a distinct hyperbolic reflector that coincides with the curved top of the tank. Scans across the length of a UST will typically record a distinct flat reflector whose distance corresponds to the length of the tank.
Click here for a full video presenting the procedures and results of a UST investigation.
Pyramid is an expert in using geophysical methods to located metallic tanks, buried drums, and similar objects. Our integration of GPS technology with the most up to date geophysical equipment allows us to rapidly investigate sites for unknown objects.
