235 Advancing the Understanding and Management of Groundwater Pollution with Arsenic and Other Geogenic Contaminants Using Geospatial Tools, Machine Learning, and Data Science, Part I

The growing trend of data aggregation and analysis, along with emerging technologies like machine learning, has significantly improved our understanding of groundwater basins, enabling better assessments of water quality for direct consumption and treatment in groundwater supply management.

Wednesday, 22 October 2025
8:00 AM - 12:00 PM
HBGCC, 210AB

WATER–SEDIMENT DYNAMICS AND HYDROGEOCHEMICAL PROCESSES INFLUENCING THE MOBILITY OF ARSENIC AND OTHER TRACE ELEMENTS IN VOLCANIC BASINS OF THE CENTRAL BOLIVIAN ALTIPLANO

Paper number: 235-4
Program: Technical Sessions
Time: 8:50 AM – 9:05 AM

Authors

Abstract

The Sajama, Turco, and Desaguadero Medio basins are located within the Central Bolivian Altiplano, within an expansive high plateau landscape that includes the well-known Sajama volcano, which has an altitude of 6,542 m.a.s.l., and extensive high-altitude wetlands serving as important water reservoirs sustaining ecosystems at elevations from 3,860 to 4,184 m.a.s.l. its volcanic origin and geothermal activity, the region is susceptible to geogenic contamination, particularly from arsenic (As), boron (B), lithium (Li), and antimony (Sb), which are mobilized through rock–water interactions and hydrothermal processes. This study aims to assess natural contamination levels and their impact on hydrogeochemistry using a combination of aqueous and sediment analyses. A total of 132 water samples were collected from lakes, rivers, springs, thermal springs, and wells. The temperature (5.1–31.5 °C), pH (5.9–11), electrical conductivity (56–29,680 μS/cm), and oxidation-reduction potential (ORP). Dissolved element concentrations varied widely: As (0.004–1,900 μg/L), B (28–28,155.7 μg/L), Li (0.019–2,810 μg/L), and Sb (0.002–98 μg/L). Thirty river and profile sediment samples were digested with Suprapur HCl/HNO₃, using cold and hot extractions at 70 °C for 24 hours in a Digiprep system. Sediment analysis revealed notable accumulation in the Sajama and parts of the Turco River: As (6.7–2,006.6 mg/kg), B (21.1–419.2 mg/kg), and Li (0.002–37 mg/kg). In contrast, lagoon sediments showed lower values: As (14.7–19.8 mg/kg), B (27.2–33.5 mg/kg), and Li (5.1–6.1 mg/kg). Geothermal fluids showed elevated As (18–73.6 mg/kg). Geoaccumulation indices (I geo) and enrichment factors (EF) indicate high levels of As and B contamination in fluvial sediments of the Sajama and Turco Rivers. The concentration of Lithium (Li) shows low to moderate EF and Igeo, with the highest accumulation observed in the Junthuma River, associated with geothermal sources. The hydrogeochemistry of the system reflects a complex interaction between geothermal activity and additional inputs from sedimentary and volcanic rocks. The enrichment and accumulation of As and B in the fluvial sediments of the Sajama basin and part of the Turco basin appear to result from the continuous input of geothermal waters. The fine-grained sediments and deposited organic matter contribute to this accumulation, underscoring the dynamic geochemical environment of the basins.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412007

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