Groundwater contamination can remain undetected for long periods of time. This makes cleanup of a contaminated water supply difficult, if not impossible. If a cleanup is undertaken, it can cost thousands to millions of dollars.

Once the contaminant source has been controlled or removed, the contaminated groundwater may be treated in one of several ways:

• Containing the contaminant to prevent migration;
• Pumping the water, treating it and returning it to the aquifer; and/or
• Leaving the groundwater in place and treating either the water or the contaminant.

A number of technologies can be used to treat groundwater. They most frequently include air stripping, activated carbon adsorption and/or chemical treatment with filtration. Different technologies are effective for different types of contaminants, and several technologies are often combined to achieve effective treatment. The effectiveness of treatment depends in part on local hydrogeological conditions, which should be evaluated prior to selecting a treatment option (U.S. EPA, 1990a). Not all contaminated groundwater can be treated successfully with current technology.