An Integrated Analysis to Delineate Groundwater Flow Systems and Recharge Dynamics in the Chili River Sub-Basin, Southern Peru

Groundwater is a critical resource in the arid Chili River sub-basin (3246 km2) in Arequipa, southern Peru, yet the aquifer systems, their recharge mechanisms, and chemical evolution remain poorly characterized. This study integrates hydrogeological mapping, major-ion hydrochemistry (31 samples from springs and wells), and stable-isotope tracing (δ18O and δ2H, 11 sources) to delineate aquifer types, groundwater flow systems, and recharge dynamics across an elevation gradient of 2000–4000 m a.s.l. Three principal aquifer groups were identified: unconsolidated porous aquifers beneath the Arequipa urban area, fracture-controlled volcanic aquifers associated with the Chachani, Misti, and Pichupichu volcanic complexes, and sedimentary fractured aquifers of the Yura Group. Piper and Stiff diagrams reveal a chemical evolution from calcium-bicarbonate waters at high elevations to sodium-chloride waters in the lowlands, while scatter-plot analysis distinguishes local, intermediate, and regional flow systems. Elevated boron concentrations linked to borate deposits on Pichupichu volcano pose a potential health risk in supply springs such as La Bedoya. Isotopic signatures confirm that wells are recharged predominantly by high-altitude rainfall (>4000 m a.s.l.), whereas springs integrate water from multiple elevations through fractured volcanic formations. These findings provide a scientific basis for recharge-zone protection, abstraction planning, and water-quality monitoring to sustain groundwater supply under increasing urbanization and climatic variability.