10/06/2026
Drops of Knowledge:
An aquifer is an underground body of rock, sand, soil, or sediment saturated with groundwater. It is not an underground river. Groundwater is recharged through rain, water seepage from soil, or neighboring water bodies. They are an important source of our drinking water which we pump through private or public wells.
There are two general types of aquifers:
Unconfined - also called “water table aquifer” because their upper water surface rises and falls with the water table (vertically). Since they are generally closer to the ground, they are also more subject to environmental conditions such as drought and contamination.
Confined – Layers of impermeable material are both above and below the aquifer, causing it to be under pressure so the water will rise above the top of the aquifer. Confined aquifers cannot be recharged directly by rainwater but in general are recharged at areas where they are in contact with a permeable surface that allows water in.
In Iowa, a “deep well” is defined by the presence of a “low permeability unit,” or confining unit. The DNR lists 3 common confining units: till, shale, and siltstone.
Carbonate bedrock (limestone and dolomite) are not considered low permeability. Clay, very common in Iowa and in alluvial aquifers does not meet the definition for a deep well due to its noncontinuous nature. Karst geology found in NE IA is particularly sensitive and wells even 300-500 feet deep are considered “shallow” due to the fractures in the bedrock.