Mines do *NOT* come on-line quickly and always on schedule (and leaching is, AFAIK, a slow but cheap process with low annual yields and bad effects on the watershed). Note: not an expert on leach mining.

World-nuclear.org has this to say on the matter:

In the USA the production life of an individual ISL well pattern is typically one to three years. Most of the uranium is recovered during the first six months of the operation. The most successful operations have achieved a total overall recovery of about 80% of the ore, the minimum is about 60%. In Australia individual well patterns can operate from between 6 and 18 months with target recoveries of around 70% in 12 months.

Plenty fast.  The effects on groundwater depend on how much of the acid etc. is neutralized or otherwise cleaned up.

I am no chemist, but if an acid leach recovers radium along with uranium, the radium and radon content of the groundwater will be reduced immediately.  In the long run, less uranium means less radium and less radon.

The long cancer rates for uranium miners from the boom were startling high, and provide some basis for the LMT model.

Not true. Early miners worked in poorly ventilated mines of very high grade ore. They received radiation doses to the lungs vastly higher than the optimum dose for radiation hormesis indicated by Dr Cohen’s study.

The results of the study were described by their own authors as “surprising” and “stunning”: Clear evidence of radiation hormesis. It looks like Bernard Cohen has been vindicated after all.
“We were certainly not looking for a hormetic effect,” says co-author Joel H. Popkin of Fallon Clinic and St. Vincent Hospital in Worcester. “Indeed, we were stunned when the data pointed to that conclusion in such a strong way.”

http://enochthered.wordpress.com/category/radiation-hormesis/
http://www.radonmine.com/pdf/riskinperspective.pdf

Modern mines are well ventilated.