Workshop Panel Grounding/Bonding
I need your advice concerning the panelboard in my detached workshop building. It is powered from a 100A 2 pole breaker in the main panel and run underground using triplexed, direct burial, USE wire (XPLE insulation, 2#2, hot, & 1#4 Neutral, aluminum conductors) wire (No conduit). This is a 3 wire circuit with no grounding conductor and was probably installed about 1985 (based on the date on the wire). The workshop panel has a 100A main breaker for a disconnect and a #4 bare copper ground wire from the panel ground bar that disappears into the floor slab. It appears that when originally installed, the neutrals and ground were bonded together but later some one separated them and removed the neutral bonding screw ( the screw was found laying in the bottom of the panel and several circuit grounds were spliced to reach the ground bar).
The building contains copper water (above and blow grade) piping, above ground steel gas piping, telephone and cable TV. None of these are currently grounded in this building but that could easily be fixed. It is not feasible to add a new grounding conductor from the main panel because the feeder is all under either a concrete driveway or the floor slab of the workshop building itself.
Should I bond the grounds to the neutral bus and panelboard enclosure or leave them separated?
Should I bond the water and gas piping to the ground bar in the panel?