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Glossary of Terms

Aquifer: A geologic unit capable of storing and transmitting water in sufficient quantities to allow viable extraction as a water supply. Aquifers can consist of porous material of relatively high hydraulic conductivity (sand, gravel), or fractured rock. "Aquifer" is a derivative of the Latin word meaning "water carrier."  

Aquifer sensitivity: Sensitivity can be defined as the ability of the aquifer to transport pathogens rapidly for long distances in the absence of a hydrogeologic barrier (U.S. EPA definition). Karst, fractured rock, and gravel aquifers are considered to be sensitive. 

Aquifer vulnerability: Vulnerability is a measure of the natural protection an aquifer has in the form of overlying layers with low permeability (aquitards). Vulnerability is usually expressed in a qualitative way (i.e. high/low, or by means of numbers on a scale), and mapped in the form of vulnerability maps.

Aquitard: A hydrogeologic barrier, which protects aquifer(s), is made of fine-grained soil particles and have a low ability to permit groundwater.

Groundwater recharge: Recharge is defined as part of precipitation, which infiltrates into the subsurface. The amount of recharge depends on the amount of infiltration, temperatures, type of surficial soils, and topography. The distribution of recharge to the various aquifers is controlled by the hydrogeology. 

Well capture zone: The area of land around the well that is supplying groundwater to this well as defined by a groundwater model. The well capture zone is defined for specific times, when the well is pumped at its permitted rate. A well capture zone depends on the hydrogeology, the flow system, the recharge, the pumping rate, and the depth of the well screen.

Time of Travel : Time of Travel is identified by computer model to estimate how long it will take for water particles to reach the well when the well is pumped at maximum permitted rates. The following time frames are typically identified for WHPA: 50 days, 1 year, 2 years, 5 years, 10 years and 25 years.

Wellhead Protection Area (WHPA): The area around a well or well field within which groundwater protection measures are applied. This zone is normally, but not always, part of a well capture zone. It is usually subdivided into different zones which may be defined in terms of travel time from a contaminant entry point to the well, corresponding to different types of contaminants. For example, the innermost zone (closest to the well) may correspond to biological contaminants, the intermediate zone to degrading petroleum products, and the outermost zone to persistent chemicals. The outermost protection zone may correspond to the well capture zone. A wellhead protection zone can be delineated by approximate graphical methods, or more accurately by use of groundwater model.