Worked in an industrial facility for many years. Step 1: Do a GOOD search to see if there is any construction or repair work going on that COULD intersect with your runs. Might save lots of work. I have had some success tracing 'lost' conduits with an underground pipe tracer (like the ones the utility uses). They inject a strong signal onto the pipe (which you might have to isolate from the grounded panel) and depending on the amount of 'clutter' under the concrete you may be able to trace it quite aways or pick it up from the other end.
