You need to drill 100 holes in post- tension reinforced structures, how would you do it?
If you had to locate and map re-bar in concrete, how would you do it?

You need to locate and map metallic and nonmetallic pipes, how would you do it?

The easy answer is GPR.

GPR provides very rapid, high resolution mapping of the shallow concrete subsurface. Results are displayed in 2D or can undergo computerized post processing for 3D information.

The GPR radiates short energy pulses into the ground from a transmitting antenna. This energy {wave}, propagates at velocity related to the electrical properties of other subsurface materials.
When this wave encounters the interface of two materials having different dielectric properties, a portion of the energy is reflected back to the surface, where it is detected by the receiver antenna and transmitted to a control unit for processing and display.

GPR is the reliable way to locate depth and orientation of features buried in concrete.

GPR is not without limitations. Exploration depth can be limited by soil or water with a high conductivity. Detection ability depends on a dielectric contrast between the subsurface feature and the surrounding material. Closely spaced survey lines are required along with a relatively smooth surface.