Basics of Environmental Sampling and Analysis - Fundamentals of Environmental Sampling and Analysis - page 33

water for site clean-up (recovery well), injection of water or disposal of chemicals
(injection wells), or water level measurement and water quality sampling
(observation and monitoring wells). A piezometer is a special small diameter,
nonpumping well used to measure the elevation of water table or potentiometric
surface.
Figure 2.5 shows a typical monitoring well and several terminologies one should
be familiar with for groundwater sampling. The steel or PVC plastic pipe that
extends from the surface to the screened zone is called the casing.Thewell screen,a
portion of the well that is open to the aquifer, is typically a section of slotted pipe
allowing water to flow into the well whereas coarse soil particles are screened out.
The annular space around the screen, often filled with sand or gravel to limit the
influx of fine aquifer materials, is termed the filter pack. Above the filter pack is an
annular seal, which is the seal around the annulus of the well casing. It is usually
cemented up to the surface with a low permeability material, such as bentonite clay,

Protective
post

Locking lid
Venting cap

Protective
cover

Concret slab

Concret

Well casing

Annular grout

Centralizer

Fine sand

Bentonite seal

Fine sand

Filter pack

Well screen

Sump

Figure 2.5 Schematic of a monitoring well (adapted from the Louisiana Department of Environ-
mental Quality, 2000)