Hello Javier, I think it depends on your type of groundwater. Based on my experience, Tritium is not preferable for groundwater dating in volcanic system due to its short half life. For small thickness of unsaturated zone (below meters or tens meters), CFC concentrations are approximately in equilibrium with air, and as the thickness of the unsaturated zone is great (over ten meters), CFC concentrations will fall greatly with depth. Due to their significance results for shallow groundwater, maybe you should be start looking for 14C dating methods for deeper/older groundwater dating for comparison.

You could find any more related info in http://pubs.usgs.gov/fs/FS-134-99/

Hope it helps.

Cheers

In your case C14 is the best method

Well,

https://iop.figshare.com/articles/_Comparison_of_the_tritium_concentration_a_EACs_equivalent_air_concentrations_of_CFC_12_b_and_SF_sub/1011859/1

Regards