Figure 1 Definitions

Well seal:
A seal is a cylindrical layer of material, usually cement, bentonite, or clay, that surrounds the casing up to a certain depth in the well. It prevents runoff or other contaminants from entering the well, and serves to further protect the casing.

Well Screen:
Well screen is a cylindrical sieve- like structure that serves as the intake portion of the well. It is a metallic pipe that has holes or perforated sections or slotted sections that is placed on the water- carrying zones of the aquifer.

Filter pack:
A filter pack is made up of sand or gravel that is smooth, uniform,clean, well-rounded, and siliceous. It is placed in the annulus of the well between the borehole wall and the well screen to prevent formation material from entering the screen.

Vadose Zone:
This is the zone that contains water under pressure less than that of the atmospheric pressure. It is the layer of soil between the water table and the ground surface.

Potentiometric surface:
This is an imaginary surface
representing the total head of groundwater in a confined aquifer that is defined by a level to which water will rise in the well.

Source: Adapted from Groundwater and Wells, Second Edition by Fletcher G. Driscoll, Ph.D.