Answer:
You can have an imaging company locate and I.D. them for you. There are several technologies to choose from. X-ray will give easily readable results but is hazardous and cannot give the depths of items in the slab. Radar is safer, more cost effective, and gives a depth, but it has a hard time imaging where there are massive amounts of tightly-spaced rebar in the slab. check out www.srimaging.com.