zero air voids curve

The curve showing the relationship between dry unit weights and corresponding moisture contents, assuming that all of the voids are completely filled with water. (US Dept of the Interior- Bureau of Reclamation)

zero lot line

A municipal zoning category wherein a building or other fixture may abut the property line. (HardwickAssociates)

zero-coupon mortgage

A long-term commercial mortgage that defers all payments of principal and interest until maturity. (Federal Reserve Bank- SF)


OSHA's Toxic and Hazardous Substances Tables (Z-1, Z-2, and Z-3) of air contaminants; any material found on these tables is considered hazardous. (US EPA- Pesticides)


A geographical area shown on a Flood Hazard Boundary Map or a Flood Insurance Rate Map that reflects the severity or type of flooding in the area. (Federal Emergency Management Agency) A specific area within a municipality or other jurisdiction which conforms to certain guidelines regarding the use of property in the zone. Typical zones include single-family, multi-family, industrial, commercial and mixed-use. (HardwickAssociates) A space or group of spaces within a building with any combination of heating, cooling, or lighting requirements sufficiently similar so that desired conditions can be maintained throughout by a single controlling device. ( The occupied space or group of spaces within a building which has its heating or cooling controlled by a single thermostat. (US Environmental Protection Agency) The smallest geographically designated area for analysis of transportation activity. A zone can be from one to ten square miles in area. Average zone size depends on the total size of study area. (US Dept of Transportation- Federal Highway Administration) An area within the interior space of a building, such as an individual room(s), to be cooled, heated, or ventilated. A zone has its own thermostat to control the flow of conditioned air into the space. (US Dept of Energy)

zone of accumulation

The layer in a soil into which soluble compounds are moved and deposited by water. (US Dept of Agriculture- Natural Resources Conservation Service)

zone of aeration

The comparatively dry soil or rock located between the ground surface and the top of the water table. The zone of aeration is not saturated with water because its pores are filled partly by air and partly by water. (US Dept of the Interior- Bureau of Reclamation)

zone of decomposition

Surface layers in a soil in which organic matter decays. (US Dept of Agriculture- Natural Resources Conservation Service)

zone of leaching

The layers in a soil from which soluble nutrients are removed by water. (US Dept of Agriculture- Natural Resources Conservation Service)

zone of saturation

The layer beneath the surface of the land in which all openings are filled with water. (US EPA- Pesticides) The soil or rock located below the top of the ground water table that is saturated with water. See water table. (US Dept of the Interior- Bureau of Reclamation)

zoned earthfill

(aka zoned embankment) An embankment dam composed of zones of selected materials where the permeability of the material increases to the upstream or downstream face from the relatively impermeable core material. (US Dept of the Interior- Bureau of Reclamation)


The ability of local governments to specify the use of private property in order to control development within designated areas of land. For example, some areas of a neighborhood may be designated only for residential use and others for commercial use such as stores, gas stations, etc. (Ginnie Mae) The classification of land by types of uses permitted and prohibited in a given district, and by densities and intensities permitted and prohibited, including regulations regarding building location on lots. (US Dept of HUD) Local laws established to control the uses of land within a particular area. Zoning laws are used to separate residential land from areas of non-residential use, such as industry or businesses. Zoning ordinances include many provisions governing such things as type of structure, setbacks, lot size, and uses of a building. (US Dept of HUD) The right of a municipality to regulate and determine the compatible character and use of property. (Old Republic National Title Insurance Co) The combining of rooms in a structure according to similar heating and cooling patterns. Zoning requires using more than one thermostat to control heating, cooling, and ventilation equipment. (US Dept of Energy) Identification of areas of specified uses or restrictions. (US Dept of the Interior- Bureau of Reclamation)


Small, usually microscopic animals (such as protozoans), found in lakes and reservoirs. (US Dept of the Interior- Bureau of Reclamation)