In 2001, the U.S. federal government lowered the maximum contaminant level (MCL) for arsenic in U.S. drinking water from 50 micrograms/liter to 10 micrograms/liter. The change occurred because recent research has shown that long-term exposure to arsenic is toxic to humans, even at extremely low concentrations. Public water suppliers have until January 2006 to comply with this new federal standard. In Minnesota alone, approximately 100 public water systems that rely on groundwater as their source currently exceed the new MCL for arsenic. Because the construction of a water treatment facility capable of removing arsenic can cost $1 million or more, Minnesota's small water suppliersﾗ located primarily in economically challenged rural communitiesﾗare faced with a severe financial burden in complying with the new drinking water standards. Minnesota's private wells also have widespread natural arsenic contamination. The authors report on research conducted at the University of Minnesota, in cooperation with state and local governmental agencies, to develop a better scientific understanding of the causes of arsenic contamination in Minnesota drinking water. The immediate, practical consequence of this research is the development and evaluation of potential low-cost methods for public water systems to meet the new federal drinking water standard for arsenic. Low-cost compliance options considered by the authors include changing well operation practices and drilling new wells at different depths or locations. Similar options also may be available for private wells.

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