For nearly two decades at the Grand Canyon, tourists, employees, and children on tours passed by three paint buckets stored in the National Park’s museum collection building, unaware that they were being exposed to radiation.

Although federal officials learned last year that the 5-gallon containers were brimming with uranium ore, then removed the radioactive specimens, the park’s safety director alleges nothing was done to warn park workers or the public that they might have been exposed to unsafe levels of radiation.

In a rogue email sent to all Park Service employees on Feb. 4, Elston “Swede” Stephenson — the safety, health and wellness manager — described the alleged cover-up as “a top management failure” and warned of possible health consequences.