Hi 2 Cents. C13 is a carbon isotope. The small letter “d” may mean “Tartaric Acid” but can’t be sure of that as this is a little beyond my chemistry knowledge.

As to Bq/l that may be a British unit of measuring, but have no idea as to its meaning.

As to CO2 being a carrier of deep radon to the surface I’m not sure if that is being accepted as the only method. Radon 222 (this is the gas were talking about) has been found at Mammoth Lakes and is associated with the breaking of rocks in that area although I’m not sure if that is the only source. I know Radon 222 has been found in well water in which no CO2 was found. Of course the CO2 could have dissipated leaving the radon in the well. Take Care…Don in creepy town