Xenobiota: Any biotum displaced from its normal habitat; a chemical foreign to a biological system.
Yard Waste: The part of solid waste composed of grass clippings, leaves, twigs, branches, and other garden refuse.
Yellow-Boy: Iron oxide flocculant (clumps of solids in waste or water); usually observed as orange-yellow deposits in surface streams with excess iron content. (See: floc, flocculation.)
Yield: The quantity of water (expressed as a rate of flow or total quantity per year) that can be collected for a given use from surface or groundwater sources.
Zero Air: Atmospheric air purified to contain less than 0.1 ppm total hydrocarbons.