Stephenson calculated potential exposures over 1,400 times the NRC's safe level for and over 140 times the safe level for adults.
He said he pressed park superintendents to take action, submitted an Inspector General complaint, contacted the FBI, and wrote to every member of Congress.
Lacking protective clothing, they purchased dish-washing and gardening gloves, then used a broken mop handle to lift the buckets into a truck, Stephenson said.
Stephenson said they detected a low-level site within the building and traced it to the three buckets, which Park Service technicians had inexplicably returned to the building after dumping their contents."You could hear their meters going off," Stephenson said.
Davis, the Park Service spokeswoman, declined comment on those details.
For nearly two decades at the Grand Canyon in Arizona, 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 five-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.
"If you were in the Museum Collections Building (2C) between the year 2000 and June 18, 2018, you were 'exposed' to uranium by OSHA's definition," Stephenson wrote.
"The radiation readings, at first blush, exceeds (.
Stephenson said specialists apparently had no Geiger counter, so they drove to Utah to pick up a Ludlum meter, which also measures radiation output.
The technicians reached the Grand Canyon several days after his call, on June 18.
A spokesman for OSHA confirmed an investigation is underway, but declined to provide any other information.
Stephenson, a military veteran who is certified as an occupational safety and health technician, was in a similar controversy during his time in the Navy.
In his letter to colleagues, Stephenson apologized for the untimely notice.