The DWI law can be located in the NC General Statutes, § 20‑138.1. In summary, the State is required to demonstrate that while operating a vehicle in a public place (which includes your own driveway), you were either a) impaired by a substance; b) had a BAC of .08 or higher from a chemical analysis after consuming enough alcohol; or c) had any quantity of a Schedule I controlled substance or its byproducts in your blood or urine. Unfortunately, this implies that in North Carolina, you may be convicted of a DWI for drug use that occurred days or weeks prior to driving if it can be identified in your blood or urine. However, if there was no legal justification for the chemical analysis in the first place, your attorney may be able to have the evidence thrown out.