Hi，Paulo,

Radioactive isotopes of Argon and Krypton in conjunction with Radiocarbon isotopes (including stable isotope of carbon) can be used for groundwater age dating. This recent technological development has enabled a full scale coverage of groundwater age from a few years to 1.3 million years.

Check this paper to find the oldest groundwater age ever determined in China and other papers there.

Good luck!

Thanks Dear Zhonghe Pang, I appreciated it. I'm going to read your PDF. Thanks a lot and best regards!

I don’t know much about Thomas Aley since I left Missouri, but he did some amazing studies in Karst hydrology in Missouri Ozarks and probably elsewhere using fluorescent dyes. He developed an extended paper with a title of approximately Water Tracers Cookbook. His work as I remember used fluorescein and activated charcoal packets to collect the dye through time. Fluorescein apparently does not break down much in the dark of karst underground streams. One or more of his studies found dye response beyond the surface hydrology boundaries. I am not sure if he used the tracers you have special interest in. More specifics on Aley — https://www.ozarkundergroundlab.com/assets/thomas-aley-resume.pdf