The tests found levels of uranium more than 10 times the legal drinking water standard in one monitoring well a half mile north of the mine. Though the health effects of specific levels are not well understood, the EPA says long-term exposure to high levels of uranium in drinking water may cause cancer and damage kidneys. At the mine itself, wells tested as high as 3.4 milligrams per liter – more than 100 times the standard. That's in an area where ore was processed with sulfuric acid and other toxic chemicals in unlined ponds.