What is a sand and gravel well?

Figure 1 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 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 from 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 screens can also be made out of other materials, like PVC. 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 in 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 PrivateWellClass.org.