Readings on Radon

http://energy.cr.usgs.gov/radon/radonhome.html
Information on Radon geology and occurrence in the US

http://www.epa.gov/radon/index.html
http://www.epa.gov/iaq/radon/rnwater.html
www.epa.gov/safewater/radon.html
Several EPA pages on health and home protection, the new standards
Also has links to the NAS studies