The OWP oil/water interface probe is used to determine the thickness of hydrocarbons.
It consists of a vibrating wire displacement sensor encased in a sealed body. The body contains a telescopic outer PVC pipe fitted with two flanges and an inner stainless steel rod.
One end of the rod is attached to the flange while the other is connected to a displacement sensor attached to the other flange. As deformation occurs, the telescopic pipe moves with the soil causing the rod to operate the displacement sensor.