Earth and Atmospheric Sciences, Department of


Date of this Version



Earth Science Notes No. 7, April 2004. Nebraska Natural Resource Surveys, Conservation and Surveys Division.


Copyright (c) 2004 University of Nebraska.


Because arsenic (As) in drinking water is considered a primary contributor to cancer in humans, the U.S. Environmental Protection Agency (EPA) recently lowered the maximum contaminant level (MCL) for arsenic from 50 micrograms per liter (μg/L) to 10 μg/L (1 μg/L ~ I part per billion: ppb). This MCL will become effective in 2006. On a national scale, EPA has estimated that of the 74,000 public water supply systems regulated by this MCL, approximately 4,000 systems will have to make changes to comply with it. Of the affected systems, 97 percent are small systems that serve fewer than 10,000 people each. The average increase in household cost for water that meets the new MCL depends on the size of the water system and how many people it serves. For small community water systems (serving fewer than 10,000 people), the increase in annual household cost is expected to range between $38 and $327. For community water systems that serve more than 10,000 people, annual household costs for water are expected to increase from $0.86 to $32.

There have a been a number of national and regional evaluations of the occurrence of arsenic in groundwater and drinking water with in the United States. These data suggest a complicated distribution pattern for arsenic. Arsenic concentrations greater than 10 μg/L are apparently more common in the western United States than in the eastern part. Detailed investigations in several states suggest that arsenic concentrations exceed 10 μg/L more often than previously thought. Data for Nebraska indicate arsenic concentrations are expected to be greater than 5 μg/L in at least 25 percent of groundwater samples in the majority of counties.

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