A house that is being constructed is being built on ground that is only 18" deep before it hits bedrock. The rebar can't be used as the grounding electrode because there is a vapor barrier below the concrete slab. There are no copper pipes to use either. We can't use plates or horizontal ground rods because those need to be at least 30" deep.
Is there a grounding method that would work for this case? Will drilling into the bedrock be acceptable? I've been looking through section 250 of the NEC and haven't found anything that could help.