Some wells finished in shallow aquifers can contain high levels of bacteria, nitrates, pesticides and other chemicals and organisms. Any of these contaminants can adversely impact health if consumed.
Even older wells finished in currently safe aquifers can be affected when steel well casing used in the well's construction corrodes and the casing develops small leaks that allows poor quality shallow groundwater to enter the well.
Many farms and homes in Iowa obtain their water from bedrock wells. Deep bedrock wells are generally safe water supplies because they tap deeper aquifers that have natural geologic barriers in place that helps keep contaminants from entering the aquifer. But in some areas of our state, shallow bedrock aquifers exist. Some of this bedrock is defined as "Karst".
Karst bedrock is characterized as bedrock that is close to the land's surface and contains a vast network of underground drainage systems that have direct connections to the land's surface.
In areas of Karst, much of the rainfall that would normally flow to rivers and streams, directly or indirectly flows into the shallow bedrock and becomes part of the groundwater some water wells may utilize. Some of the water that originates at the surface - possibly near sources of contamination - flows undetected into the ground.
This water can contain contaminants that are found on the land's surface and those not bound or utilized by the areas soils and land cover. Once in the ground, this water that was once on the surface becomes part of the groundwater supply.
A well that obtains part or all of its water from a shallow aquifer can have higher levels of contaminants when compared to deeper wells in the same area.
Anytime you consume water that contains unsafe levels of any contaminant, you increase your risk for negative health effects.