Conceptual model of groundwater flow in a volcanic-sedimentary aquifer system of the Andean region of Chimborazo, Ecuador

Abstract

The Chimborazo volcano is located in Ecuador's northern Andes and is one of the world's tallest mountains. The central valley of Riobamba's morphology, structure, and groundwater flow networks are all influenced by the evolution of this stratovolcano. Both the urban and rural populations in this area rely on groundwater extracted from volcano-sedimentary aquifers. This study presents a conceptual model of the groundwater flow system in the lower Chambo River basin (LCRB) based on the interpretation of geological, hydrogeological, hydrochemical, and stable isotope (δ18O and δ2H) data from 23 wells, 10 springs, two sources of surface water, and rainwater. The Tertiary-Quaternary volcanic-sedimentary infill of the Inter-Andean Valley, that overlies the Jurassic-Cretaceous metamorphic bedrock of the Eastern and Western cordilleras, gave rise to three multilayer aquifers (Llo-Guano, Riobamba, and Yaruques). In these aquifers, groundwater flows from the recharge of Chimborazo glaciers to deep circulation zones of low-elevation lands in Riobamba. In this pathway, groundwater evolves from acidic - low temperature - low electric conductivity bicarbonate waters to alkaline - high temperature - high electric conductivity sulfate waters discharged in the Chambo River. The stable isotope data confirmed the hypothesis of different types of water changing and interacting in the flow direction, demonstrating a dynamic hydrogeological system that evolves from the recharge area in Chimborazo, Igualata, and Altar volcanoes to the discharge area in the Chambo River.