Iran-Water Resources Research

Iran-Water Resources Research

Assessing the Age of Karstic Groundwater in South West of Lorestan Province Using Tritium Isotopes and Hydrogeochemical Methods: Inconsistencies Between the Two Approaches

Document Type : Original Article

Authors
1 Ph.D. Student in Hydrogeology, Department of Minerals and Groundwater Resources, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
2 Assistant Professor, Department of Minerals and Groundwater Resources, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran.
Abstract
Karst groundwater resources in Lorestan Province (west Iran) are one of the most critical drinking water sources in the region. However, no comprehensive study has yet been conducted to assess their age and quality. To address this gap, the present research employs tritium isotopes (³H) and hydrogeochemical indices to analyze the relative age and quality of these resources. Twelve groundwater samples, including seven sulfurous, three non-sulfurous, and two saline samples, were collected in 2023 and analyzed for their ionic and isotopic compositions. Tritium data and chemical indicators (SO₄/Cl, Na/Cl, Mg/Ca ratios, EC, and major ion concentrations) were analyzed to determine relative age, origin, and mixing patterns. Piper diagrams, ion scatter plots, and saturation indices of calcite, dolomite, and gypsum were used to interpret geochemical processes and water-rock interactions. Results indicated that most groundwater samples are of modern age (tritium: 1.31–3.07 TU), with a few showing mixed modern–submodern characteristics. The dominant bicarbonate type reflects carbonate origin and recent precipitation recharge, while chloride-sodium (samples S6, S7) and sulfate-chloride-calcium types (samples W2, S2) suggest influence from the Gachsaran Formation or contamination. Notably, samples S6 and S7 exhibited high tritium and salinity, indicating rapid infiltration of recent rainfall into the Gachsaran Formation and localized salt dissolution. Furthermore, the characteristics of samples W2 and P1, including high SO/Cl ratios and elevated tritium concentrations, indicated potential contamination and the introduction of pollutants into the groundwater system. Samples W1, P2, and S3, characterized by simple ionic compositions and high tritium levels, represented young waters, whereas samples S1, S2, and S4, with more evolved ionic compositions and lower tritium concentrations, indicated mixed sources and intermediate behavior in terms of age and hydrochemical composition. Other samples, such as P3 and S5, with moderate SO/Cl ratios and tritium levels, lie at the boundary between young waters and mixed sources, likely influenced by mixing, surface recharge, anthropogenic contamination, or water inflow through faults.
 
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  • Receive Date 18 May 2025
  • Revise Date 14 July 2025
  • Accept Date 17 August 2025