Very refreshingly, the anti-mining NGOs have, according to this article, begun to adjust their perspective regarding the potential "threat" posed by uranium mining in northern Arizona: Initially, Shuey et al. claimed the fact that the low-flow Horn Creek spring (0.1 gallons/minute) with something like 30 ppb dissolved uranium posed a clear and present danger to hikers in the Canyon, not to mention 25 million people downstream of the Grand Canyon National Park. Now the same people, have fallen back quite a bit from their earlier position, and are speculating that if a whole bunch of these springs started putting out 30 ppb uranium at 0.1 gallon per minute, then maybe we'd have a real problem downstream. That position is a distinct improvement -- and is getting closer to the truth of the matter; namely, that there is no real threat to anyone's drinking water from uranium-bearing breccia pipes, or from breccia pipe uranium exploration or mining in northern Arizona.

The original South Rim spring water data can be found online at:
http://pubs.usgs.gov/sir/2004/5146/ (the USGS data)
http://public.dirxploration.fastmail.us/ (the Univ. of Nev. Las Vegas data)

And discussion that puts these data into geological and hydrological perspective can be found at:
http://www.dirxploration.com/newsmay2008.html