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GPR Locates Concrete Slab Embedments Missed by Passive Scanning

During the construction of a new auto dealership in Pennsauken, NJ, the general contractor (GC) ran into a problem. They could locate no prints or as-builts for the building addition they were working on, and there were no known sanitary lines under the floor. They were contracted to install bathrooms, so the plan was to tunnel under the building’s footer to a known sanitary line outside of the building.

The GC needed a scan of the floor before sawing the trenches. They called on the services of CSDA member Ground Penetrating Radar Systems, LLC (GPRS) to scan the floor to discover what, if anything, lay below. The floor was simply an open concrete slab on grade with sectional carpet. When GPRS technician Benjamin Iles arrived, he noticed only a couple of wall panels and no mechanical or electrical rooms nearby. He had an electrician open the wall panels but saw no conduit penetrating into the slab. With a Radiodetection RD 4000, GPRS ran a passive mode locate scan over the floor with the carpet in place. The results were negative – nothing was found below the slab. But when the area was scanned with a Conquest 1000 MHz GPR concrete scanner, several anomalies and unknown objects were revealed.

“I ended up coming across surface features that were covered over with the carpet and a bit of concrete, including several buried cleanout lids, unknown utilities running just underneath the slab, an elongated disturbance in the slab and an unknown circular lid,” said Iles. GPRS and the plumber pulled back the carpet above the anomalies and discovered cleanouts and access lids for Walker Ducts. They broke open the cleanout lids and with an Envirosight Verisite camera and duct rod they found out that the cleanout lids led to utility lines connected to the sewer outside the building – the same sewer line the GC was contracted to tunnel to. With the Bluebeam drawing app for iPad, GPRS scanned an existing floor plan and overlaid the findings by hand. The cleanout lids were later confirmed to be an abandoned sewer line just under the building’s slab, and once inspected and cleaned, it could be used. GPR helped the client save money on the project, as the original plan for tunneling under the footer could be abandoned. The GC was able to demo the floor safely, as they understood where the utilities and anomalies were located under the slab and could tie in the plumbing inside the building where they were saw cutting. Once again, a CSDA member helps to save their clients time, money and resources.

Established in 2001, GPRS is the nation’s #1 GPR company,
headquartered in Toledo, Ohio. They offer a number of
subsurface utility engineering services like private utility
locating, concrete scanning, and video pipe inspection. They
have been a member of CSDA since 2015.
CSDA GPR Contractor
GPRS, Inc.
Jami Roblejo
Phone: 610-358-0172 X405
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