Perchlorate—Drinking Water Impacts and Sources in California

Perchlorate is a man-made salt that has recently been discovered as a threat to drinking water supplies. Perchlorate is a manufactured component of solid rocket fuel and is used for explosives, fireworks, flares, and other applications. In humans and animals, perchlorate can adversely affect the thyroid. Prior to April 1997, perchlorate could not be detected in low concentrations, and little was known about either its toxicity or the extent perchlorate had contaminated drinking water supplies. Then in 1997, the California Department of Health Services developed a new analytical method to detect very low levels of perchlorate in water. Since then, this chemical has been found in the water supplies of more than 15 million people in California, Nevada, and Arizona as well as in surface and groundwater throughout the United States.

This map brings together information from the state of California and several federal agencies to help prioritize and coordinate efforts to address this emerging contaminant. State agencies have been tracking public water supply wells where perchlorate has been detected. The U.S. Environmental Protection Agency (EPA) has information on many of the major sources such as aerospace manufacturing operations that are now Superfund cleanup sites. The Department of Defense has information on former military sites throughout California. Nine areas that have been identified by U.S. EPA for further investigation can be seen in the “perchlorate discovery study areas” inset. This map and future updates provide a useful and flexible tool for communication within and between government agencies.