USGS is scheduled to release on March 27, 2009, a report on the agency's analysis of 219 contaminants and physical and chemical properties that it investigated in 2,100 private drinking water wells in 48 states. The wells tap into about half of the nation's aquifers, offering a potentially informative glimpse into toxics that residents may be ingesting.
Private wells provide water to about 15% of the US population, and their water quality is much less regulated than that of public water supplies. That tends to put much of the burden for identifying and mitigating contamination on the people who use these wells; many of them are unaware of potential threats.
For some brief background on the current study, and a map of where the wells are located, see USGS's Water-Quality of Domestic Wells in the United States.  The final report will be posted here  (where there is extensive additional information on various water quality issues), and released in a Washington, D.C., Congressional briefing that morning that is open to the public. In addition to information on contamination, the briefing will include presentations and discussion on related public health issues, including state drilling and testing requirements, well maintenance, and treatment options.
For more information on the study or the briefing, contact USGS's Jenn LaVista,  703-648-4432, or Donna Myers,  703-648-5012, or the Water Environment Federation's Nick Bardis,  703-684-2400 x7731.