Tritium as an Indicator of Modern, Mixed, and Premodern Groundwater Age

Categorical classification of groundwater age is often used for the assessment and understanding of groundwater resources. This new USGS report presents a tritium-based age classification system for the conterminous United States based on tritium (3H) thresholds that vary in space and time: modern (recharged in 1953 or later), if the measured value is larger than an upper threshold; premodern (recharged prior to 1953) if the measured value is smaller than a lower threshold; or mixed if the measured value is between the two thresholds. Inclusion of spatially varying thresholds, rather than a single threshold, accounts for the observed systematic variation in 3H deposition across the United States. Inclusion of time-varying thresholds, rather than a single threshold, accounts for the date of sampling given the radioactive decay of 3H. 

 

2019.09.12 sir20195090.200acrobat icon Tritium as an Indicator of Modern, Mixed, and Premodern Groundwater Age