The Tower Well is quite obviously not pumping "fossil water or paleowater [that has] remained in an aquifer for millennia" as suggested by the referenced article. Fossil water never ever has any tritium at all. Tritium has a half-life of only about 12.5 years: so it doesn't take long to decay below detectable limits.
The Tower Well has between 0.4 and 0.6 tritium units. The most likely explanation is that the Tower Well is tapping the regional groundwater flow that originated on top of the Rim about 50-60 years ago and is inexorably flowing to "the Valley."
This contrasts with the shallow Star Valley wells whose tritium concentrations suggest that that water fell as rain quite recently (only several years ago), as is typical of the alluvial water flows owned, or at least claimed by, the Salt River Project.