I asked Ben A.I am not familiar with the instrument they say can do the isotopic analyses for the various decay products of uranium and the uranium isotopes reported as having a significant change in values at the bedrock till interface.
Radon comes from the decay of uranium.
Radon decays to bismuth 214 and maybe radium 226. Actually on the total counts scintillometer which does not look at the different energies of the radiation from the various isotopes, the measurement being made is mostly due to Bi 214 which occurs in the decay change after the gaseous element radon which is highly soluble in water. Any movement of water will move the radon in solution to where the water goes which may be vertically up or horizontally or a mixture of those vectors. You just do not know from where the radon originated and the same goes for the solid, elemental, Bismuth 214.
I am a bit sceptical about the level of knowledge of the QP because I do not know the specifications of his instrumentation.
Ben