In a few locations in Idaho, ground water is naturally high in some trace elements such as fluoride. In southwest Idaho, elevated concentrations of arsenic, uranium and sulfate are found in some aquifers.

Non-natural contaminants of greatest potential to impact health in the state are nitrate, volatile organic compounds and pesticides, trace elements (primarily cadmium and selenium), and bacteria. Most sites with elevated nitrate concentrations are in southwest and south-central Idaho. Three percent of all sites tested in the state exceed drinking water standards for nitrate and about one third are elevated through known human influence. The most serious and wide-spread organic chemical contamination occurs in the Boise/Eagle area, around Fort Hall, and in the lower Portneuf River valley around Pocatello and Chubbuck.

Locations of wells that are regularly tested are available on the Idaho Department of Water Resources' web site at http://www.idwr.state.id.us/planpol/techserv/gwmon/prog_sites.htm.

Additional information on the state-wide monitoring network, as well as literature describing the program's findings is at http://www.idwr.state.id.us/planpol/techserv/gwmon/prog_stat.htm.