I agree with Dmatox. It seems like they tried to make it simple enough by just saying "1) Exterior underground installations." I don't understand why you think you can use NMC. If corrosion was an issue you should have gotton the permision to use NMC.
Now with all the phone calls it sounds like they will make an exception for your case if it's 18" below grade. I can't tell you if grade is the same as floor hight. But it does sound like they are tring to work with you.
Is it reasonable for some EC to save a fair amount of $$ by not followning the local amendments. IMO I think the county should hold their ground & force you to do the work to meet their rules.
Sorry to hear about your problem,
Tom
