Title from PDF title screen (viewed on Mar. 20, 2007).
At head of title on HTML title screen: Nebraska Water Science Center.
"National Water-Quality Assessment Program."
Includes bibliographical references (pages 34-38).
Mode of access: Internet at the USGS web site. Address as of 7/28/08: http://pubs.usgs.gov/sir/2006/5196/pdf/SIR20065196.pdf ; current access is available via PURL.