Oct. 29, 1999 Researchers with the U.S. Geological Survey estimate that 42 million Americans use groundwater vulnerable to low-level contamination by volatile organic compounds (VOCs). The estimate is based on the first nationwide assessment of untreated groundwater aquifers, which found VOC levels in excess of federal drinking water criteria in about 6 percent of urban wells and 1.5 percent of rural wells. The amount of human exposure to the VOCs is uncertain, according to the researchers.
The research, involving water samples collected between 1985-1995 from nearly 3,000 wells throughout the United States, will be published Oct. 29 in the web edition of the journal Environmental Science & Technology. The report is scheduled to appear in the Dec. 1 print edition of the peer-reviewed journal, which is published by the American Chemical Society, the world's largest scientific society.
Researchers examined water quality of many of the nation's principal aquifers as part of the study, according to the report's lead author Paul Squillace, a research hydrologist with the U.S. Geological Survey office in Rapid City, S.D. The sampled wells were primarily located along the east and west coasts, and in the central United States.
"The samples were collected to represent the groundwater quality in the aquifer and not the water quality at the tap," says Squillace. "This resource assessment is the first national scale assessment of [untreated] drinking water aquifers," he claims. The U.S. Environmental Protection Agency requires states to routinely monitor the quality of treated water.
The study concludes that people in the eastern half of the United States are more likely to live in areas where groundwater contains VOCs than people in the western half of the country. It also found that people living in more populated areas, the northeast and the west coast, were most likely to use groundwater containing VOCs. "The larger the population density, the greater the detection frequency of VOCs in the aquifers," notes Squillace.
"Among all wells, untreated groundwater in urban areas was four times more likely to exceed a drinking-water criterion than untreated groundwater in rural areas," according to the report.
Chlorination of public water, the most common treatment method, generally does not reduce VOC contamination, says Squillace. However, he notes, treatment facilities routinely monitor for VOCs and must use other treatment methods, such as aeration, if levels get above allowable limits. Such is not the case with private wells, he adds.
Volatile organic compounds are found in a variety of products, including gasoline, paints, plastics and solvents. The gasoline additive MTBE (methyl tert-butyl ether) and solvent compounds were "among the most frequently detected VOCs in urban and rural areas," according to the report.
"VOCs can be important environmental contaminants because many are mobile, persistent and toxic," the report points out. "The U.S. EPA has established maximum contaminant levels in drinking water for 27 VOCs because of human health concerns," it adds.
The VOCs detected in aquifers commonly are mixtures of several compounds. "Because current health criteria are based on exposure to a single [VOC] contaminant, the health implications of these mixtures are not known," Squillace emphasizes.
How much actual human exposure there might be to VOCs in aquifers is "uncertain," says Squillace. But, since so many people obtain their water from aquifers, "monitoring and proactive protection of these aquifers would seem prudent," he says.
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