Also my first idea, but I think that’d only make sense if it’s a few centuries old and completely forgotten about creating weird superstitions. There’s nothing actually dangerous about long-term nuclear waste storage, all of these markings would exist mostly to prevent people from digging in the area and potentially uncovering the waste.
Not to mention that it’d have to be a very small area, nowhere near the size of a single city – nevermind a whole US state.
A study from 1989 doesn’t apply to modern plants built 35 years later, it really doesn’t make sense to extrapolate it like this.