Do they possibly mean, this concentration of uranium while in [this] water? As the water would be a partial radiation shield/mitigation/etc, plus it's a very small concentration (though a large amount of concentrated water).
So this particular contamination of uranium is only harmful if swallowed/digested where it will accumulate. However, as it's also a lot of contaminated water, that's a big risk still, so needs cleaning up!
Biting the hand that feeds IT
