Trompetter, V.J. 2026 Reconstruction of stable isotope values from distilled groundwater samples. Lower Hutt, NZ: Earth Sciences New Zealand. GNS Science report 2026/06. 7 p.; doi: 10.21420/0BEQ-1E90
Abstract
Stable isotopes of hydrogen (δ²H) and oxygen (δ¹⁸O)are widely used to investigate groundwater recharge, flow pathways, and mixing processes. This study quantifies isotopic fractionation during vacuum distillation for tritium analysis and evaluates whether original isotope values can be reconstructed from post-distillation measurements. Samples were collected from distilled and residual fractions throughout the distillation process, and (δ²H) and (δ¹⁸O) values were measured before, during, and after distillation. The effects of water recovery, water loss, and multiple distillation cycles were investigated. Results showed a strong relationship between isotopic shift and water recovery. Typical distillation conditions produced an average isotopic shift for deuterium of about 1.7‰ ± 1‰, and 0.19 ‰ ± 0.1 ‰ for oxygen 18. Strong linear relationships between pre and post distillation isotope values indicate that original isotope compositions can be reliably reconstructed. Samples subjected to multiple distillations or experiencing large water losses exhibited greater uncertainty and are not useful for this purpose. These findings demonstrate that stable isotope data collected during routine tritium analyses can potentially be corrected and used for hydrogeological investigations, unlocking the value of historical groundwater samples for studies of recharge sources and groundwater flow (auth)
