This geophysical method is used in addition to GPR, using a Vivax-Metrotech system, specifically the Loc-10Tx (10 Watt) transmitter and a VLocPro2 receiver. The system works on at least two modes including a passive mode where the receiver detects any lines carrying current as well as an induction/conduction mode.
In the induction/conduction mode, a specific radio frequency is transmitted into a cable or pipe (either through direct connection or through inductive coupling) and that same frequency is then detected with the receiver to trace the location of the buried pipe or cable. Metal pipes are excellent conductors, therefore they frequently pick up ambient current in the ground, which makes them good line tracing targets. We attempt to locate all subsurface targets using at least two different methods, although for some subtle targets one method may be successful in locating targets while the other method is not.
Another way we have of tracing pipes involves sending a radio transmitter into those pipes using a Rodder/Sonde system. The pipes can be traced by tracking that radio signal with the line-tracing receiver. For small diameter pipes that are not made of metal or some other conductive material, we can slide a wire into those pipes and transmit a radio signal into the wire which allows us to trace those pipes.