This underground heating oil tank was detected under a concrete floor using a ground penetrating radar (GPR) unit (See figure above). If only a metal detector was used, at best it would be suspected as a potential candidate for an oil tank. Exploratory digging would be difficult due to the concrete floor. However, Since the oil tank footprint occupied almost the whole concrete floor and there were steel stairs/fences and brick walls nearby, the metal detector responses could be easily disregarded as interferences from aboveground objects and reinforcement in the concrete. As a result, the oil tank could be missed if only a metal detector was used. Fortunately, we always use a GPR with a metal detector for oil tank sweeps. As a result, this oil tank was detected without a problem.
For oil tank sweeps, its always better to use both a metal detector and a GPR than only using one of them. During an oil tank sweep, besides the possibility of missing an otherwise detected underground oil tank, the even bigger problem of only using a metal detector is false positives. It demands further expensive investigations which most likely could be avoided by also using a GPR during the oil tank sweep. To minimize your risks and troubles, use a service employing both a metal detector and a GPR for the oil tank sweep!
