There's a nurse on here named Hppygrateful, or something along those lines. She's done all kinds of research on this topic. Hopefully she'll chime in at some point. I live in Florida and they have had similar complaints/problems with nurses claiming false positives for etoh( I was one of them ). They have begun random 'special' testing: pEth, hair, nails. Personally, I'm happy about it. It's more expensive. But, it's not near as expensive as a complete evaluation because you've had a positive. I was just selected for a pEth two days ago. History is that I popped positive (within the incidental exposure range) back in April. I pulled a pEth on myself (results negative) as soon as I was notified. I was referred for an eval, pEth, hair, urine all negative. You don't get sent back to treatment immediately for a positive, but it's going to cost you to prove your innocence.
You'll drive yourself crazy worrying about it, so try not to. No one in my group has ever popped positive, but me. So, I don't think it happens often. It's just so traumatic when it does, that it tends to be awfulized. Try not to used alcohol based products ( soaps, hair products ), incidental exposure can happen when you inhale the fumes.