My husband just had a pre-employment drug screen and tested positive for THC. He has smoked before but not recently. We live in Michigan where it is legal to cultivate and use for medicinal purposes. We have a tenant who rents out our basement and grows and uses with a license. This seems to be the only explanation for the positive result, as we do come in contact with it on a regular basis.
This would not be a plausible or acceptable explanation because drug tests look at THC metabolites and not THC itself. Therefore THC would have to be ingested and metabolized by the body in order for it to be detectable on a U/A.

Was your test result confirmed using the GC/MS test? You would know this because the GC/MS would give a quantitative value.