This is a diagram of a drilled sand and gravel well.
Because this type of well is finished in a sand and gravel aquifer,
which isn't solid and will cave in, it requires the well to be
completely cased. Sand and a gravel wells differ in basic construction from
bedrock wells by having a screen at the bottom of the well and
solid casing from the surface to the screen.
This ensures that water is only entering the well through the screen.
A well screen is generally made a woven steel wire formed in the
shape of a pipe or casing. The screen has openings based on the
size of the sand and gravel grains and the aquifer.
This way it keeps sand out of the well, but water can flow
through. Sometimes screen can be made out of other materials like PVC as
well. A specific size of coarse sand or gravel, called the gravel pack,
is placed around the well screen in the wellbore to help keep the
finer sand in the aquifer from entering the well.
Some people and areas with really shallow aquifers may have a driven or
sand point well. We don't recommend them for a private drinking water supply
because they're so prone to surface influences. They're at a much higher
risk of contamination. This is especially true where the surface soils are
also sandy and there is significant surface infiltration. Sand point wells
have no grout at the surface or in the annulus that can be
used to help protect around the wellbore. If you're in an area with
a shallow aquifer that can support a sand point well, we recommend you
drill a well with the screen near the bottom of the aquifer.
This way surface infiltration into the ground will have to travel a longer
distance to get into the well decreasing your chances for surface contamination
reaching your well. The Private Well Class is a collaboration between the
Rural Community Assistance Partnership and the University of Illinois through
the Illinois State Water Survey and the Illinois Water Resource Center,
and funded by the United States Environmental Protection Agency.
The views expressed here are solely from the class authors and not endorsed
or reviewed by US EPA. For more information on private wells,
sign up for our free 10 week email course at www.privatewellclass.org.
