The New York State Department of Environmental Conservation describes vapor intrusion as the process by which volatile chemicals move from a subsurface source into the indoor air of an overlying or adjacent building. They share the fact that the subsurface source can either be contaminated groundwater or contaminated soil which releases vapors into the pore spaces in the soil. Vapors can also sometimes enter a structure by migrating from contaminated bath, shower and drinking water., , , , Th.