New Mexico Geological Society Annual Spring Meeting — Abstracts

A compilation of over 1100 tritium analyses in groundwater from wells and springs in New Mexico was analyzed with Jasechko’s (2016) method to estimate the fraction of modern (post-1953) water, referred to as Fm. A new atmospheric tritium input function for Albuquerque was developed and used with local precipitation records to create ten local tritium input functions across the state. Based on comparison with independent estimates of the fraction of modern water determined via analysis of CFCs in the Sacramento Mountains region, it is likely that Jasechko’s (2016) method underestimates the fraction of modern water to some degree. High Fm is associated with shallow alluvial aquifers along major perennial streams, and in some cases along intermittent drainages as well. This emphasizes the importance of surface water, its interconnection with shallow groundwater via focused recharge, and the vulnerability of shallow alluvial groundwater resources to processes that negatively affect streamflow. In all regions and geologic environments, Fm decreases as well depth increases. As the natural downgradient termini of groundwater flow systems, most springs show very low Fm values. There are few data available in the regions of diffuse recharge as predicted by the PyRANA recharge model for New Mexico, as these are almost exclusively high elevation areas with little development. Results from several areas of the state are presented in detail and the Fm data are discussed in terms of regional hydrogeologic understanding. Despite the large dataset analyzed in this study, much of New Mexico has no data available for tritium in groundwater, or any other comprehensive chemical analyses.

Jasechko, S., 2016, Partitioning young and old groundwater with geochemical tracers: Chemical Geology, v.427, p. 35–42, https://doi.org/10.1016/j.chemgo.2016.02.012