A team from the U.S. Environmental Protection Agency (EPA) is in North Central Montana this week trying to solve a radiation mystery that started with dead cows.

The mystery started with two cows and six calves found dead on a ranch near Brady, about 45 miles northwest of Great Falls. A test revealed that the water the cows had been drinking had radiation levels higher than normal.

Richard Graham, a radioenvironmental scientist for the EPA, is now on the hunt to solve this radiation mystery. The EPA's tests of water and soil in the area this week found nothing abnormal, and no levels high enough to have killed the cows, or pose a hazard to humans or other animals.

Graham said, "Brady's water supply is fine and there is no reason for individuals in Brady to be concerned about their drinking supply."

But that still leaves the question: what accounted for the initial test results that indicated higher levels of radiation?

Graham explained, "Actually, radiation is all around us...everywhere. Granite, the soils, the air. Here in Montana we receive, just as background, between 350, 360 to 400 millirems. (A) millirem a unit of radiation exposure."

Those natural sources could be the source of the higher levels of radiation, but scientists have to consider all possibilities, including other potential radiation sources, such as nearby nuclear missiles.

Graham said, "We are looking at that scenario but most of the missiles have been removed in the last few years from Pondera County."

While unlikely to be from the military, samples taken this week will hopefully be able to pinpoint where the radiation came from and solve at least one mystery. Results of the radiation test should take a couple months.

It's still unclear what killed the cows, and the Montana Department of Livestock is also involved in the case.

NOTE: original post inaccurately used the word "milligrams," but has now been corrected to "millirems." Thanks to emman1 for pointing out the error in the comments below.