Groundwater: How Does It Become Contaminated?

Groundwater is never a pure combination of hydrogen and oxygen atoms. As water soaks into the ground, it dissolves minerals and gases from the rock material it encounters. "Natural" groundwater contains many dissolved minerals and gases that may give it a particular taste, odor or color. Typical concentrations of most naturally--occuring contaminants pose no health risk.

Percolating groundwater can also carry human-made pollutants. Contamination can be serious if groundwater contains substances (natural or human-made) that pose a health threat--bacteria, viruses, nitrate, metals such as mercury or lead, pesticides and other synthetic organic compounds. Carelessness and lack of understanding can lead to groundwater contamination from a variety of sources including:

leaking underground petroleum pipes and tanks
use and storage of road salt
improper use, disposal and storage of hazardous materials
improper disposal of solid waste
practices such as over-application of fertilizers and pesticides
improper management of animal wastes

Since groundwater flow is generally slow, pollution may take decades to show up in a well, lake or stream. Removal of contaminants is expensive and difficult (if not impossible), so prevention of contamination is the key to maintaining groundwater quality.

(Resource: WDNR Study Guide)