Stephenson said the requests were ignored by officials, so he emailed to all Grand Canyon park staff members on Feb. 4.
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The message said, "If you were in the Museum Collections Building (bldg 2C) between the year 2000 and June 18, 2018, you were 'exposed' to uranium by OSHA's definition," CNN reported the email as saying.
The email went on to clarify, "Please understand, this doesn't mean that you're somehow contaminated, or that you are going to have health issues. It merely means essentially that there was uranium on the site and you were in its presence. ... And by law we are supposed to tell you," CNN reported.
Department of the Interior officials told CNN via a statement that uranium naturally occurs in the rocks at the Grand Canyon. Currently levels are at "background" levels, or a level that is always present in the environment. The statement says the levels are below that which could pose an issue to health and safety.
Stephenson told CNN that he found three 5-gallon buckets of uranium ore stored near a taxidermy exhibit in June. He said the buckets had been there for two decades and he contacted a park service radiation specialist about the buckets.
Stephenson claims that the radioactive readings area near the buckets were elevated, but the rest of the area was not.
Park Service officials removed the buckets on June 18 and dumped them at the Lost Orphan uranium mine from where they were gathered. Stephenson claims the workers used general gardening gloves and mop handles to move the load, CNN reported.
After filing an OSHA complaint, Stephenson told CNN OSHA inspectors arrived in November, and while wearing protective suits, found that the buckets used to store the rocks were returned to the park after emptying.
OSHA confirmed that an investigation was started on Nov. 28, but didn’t elaborate on what was discovered.
The Department of the Interior's Office of Inspector General confirmed the department received an letter from Rep. Tom O'Halleran, D-Ariz. about Stephenson's concerns and the investigation, according to CNN.
Experts say that while there was a reading, they don’t believe that there should be any concerns about visitors’ health.
"Uranium ore contains natural (unenriched) uranium which emits relatively low amounts of radiation," Anna Erickson, an associate professor of nuclear and radiological engineering at Georgia Tech, told CNN. "Given the extremely low reading (zero above background) 5 feet away from the bucket, I'm skeptical there could be any health hazards associated with visiting the exhibit."