together in a small fraction of the wells tested, as were other potentially hazardous combinations. Nearly three-quarters of the wells from human or animal waste As many as 43 million people in contained two or more contamifrom septic tanks or agricultural the U.S. get their drinking water nants at levels greater than 1/10 waste ponds. from private wells, yet the quality their health benchmarks. Mixtures Unregulated wells serve about of the water from those wells is that frequently occur at these levels 15% of the U.S. population, aclargely unknown. A new report provide a starting point, say DeSicording to USGS estimates based from the U.S. Geological Survey mone and her colleagues, for on state and other local data(USGS) provides a comprehensive evaluating which mixtures may bases. Overall, the contaminants survey of these private wells. The merit investigation for poreport also documents artential human-health eas where residents may impacts. be at risk of exposure to Jo¨rg Drewes of the Coloboth natural and humanrado School of Mines says made compounds and elethat although the new apments in groundwater. proach to assessing mixThe 214-contaminant astures is “questionable,” sessment includes dozens the reported data on of metals; radionuclides pathogen exposures are such as radon; organic important. compounds, including Possible exposure to bacpesticides such as atraterial and other sewagezine; and other comrelated contaminants from pounds of concern. Researchers sampled more than 2000 private drinking-water these wells is worrisome, Leslie DeSimone and wells in rural and urban areas. This map shows the agrees Ben Stanford, a her USGS colleagues ana- geographic distribution of fecal indicator bacteria detected postdoctoral researcher at lyzed water from more in the researcher’s samples. Green shows total coliform the Southern Nevada Water than 2000 wells sampled bacteria detected; brown shows E. coli bacteria; red shows both total coliform and E. coli bacteria; and clear shows Authority, a regional public from 1991 to 2004. no detections of either. water agency and drinkingGroundwater generally water research facility. But movessand therefore in the context of past reports on found in the groundwater were changessslowly, so levels of natuarsenic, pesticides, and other comgenerally at lower levels than the ral compounds should remain pounds in groundwater from USGS maximum contaminant levels fairly constant, DeSimone exand other researchers, the study’s (MCLs) set by the U.S. EPA for plains. The team added to existbroader findings about contamiknown human-health hazards. If ing data for areas long known to nant levels are “not that surprisno MCLs had been set for cerbe of high concern for arsenic, ing,” he says. However, this USGS tain contaminants, USGS used such as New England (DOI survey provides huge data sets, and its own human-health bench10.1021/es051972f; 10.1021/ its value lies in its breadth, Stanmarks, known as health-based es803141m). The researchers also ford adds. screening levels (HBSLs). These found in some areas detectable The report highlights the need to levels were determined in partlevels of newer human-made educate homeowners about pointnership with EPA. For example, compounds such as methyl-tertof-use treatment and other issues, USGS uses an HBSL of 1000 mibutyl ether (MTBE) and currently Drewes says. The National Ground crograms per liter (µg/L) for boused pesticides in drinking-water Water Association (NGWA) has ron. There is no EPA MCL for wells. backed proposals for tax credits for boron, but the agency has a “We identified microbial conhomeowners who test their wells. health advisory level of 600 µg/L. taminants, which are possible “Owners are responsible for their The great unknowns, says DeSiindicators of sewage contaminaown treatment devices,” says mone, are the human-health imtion, as one of the most freNGWA director Kevin McCray. pacts from exposure to mixtures of quently occurring contaminants NGWA offers best-practice guidemultiple compounds over a long of potential health concern,” lines for well owners and is workperiod of time. Some pairings, such notes DeSimone. Her team deing with the Centers for Disease as nitrate and atrazine, could react tected total coliform in about Control and Prevention to evaluate in the human body to form susone-third of 400 sampled wells, owners’ drinking-water habits. pected carcinogens, and these paran indicator of bacteria present ticular compounds were detected and possible contamination —NAOMI LUBICK USGS
USGS profiles private wells
3988 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / June 1, 2009
10.1021/es901057t
2009 American Chemical Society
Published on Web 04/22/2009
