Geochemical and isotopic study of formations aquifers in a high mountain system: the Santander Massif (Colombia)

The Santander Massif, located in the Eastern Cordillera of the Colombian Andes, constitutes a hydrogeological system important for Bucaramanga city. The water sources providing for the population originate from this mountain region. In the highest part of the study area, there is a páramo zone named the Berlín Páramo that provides different ecosystem services to the region. The geological composition of the Santander Massif consists mainly of igneous-metamorphic rocks. The main geological structure is the Bucaramanga Fault, which demarcates the Santander Massif area from the Bucaramanga Formation (dominated by Quaternary deposit). A total of 39 groundwater chemistry samples, 14 groundwater isotope samples, and seven surface water isotope samples were analyzed. The hydrochemical facies identified include calcium-magnesium bicarbonate and calcium-sodium bicarbonate. The main geochemical mineralization processes are the interaction between CO₂ and water, and silicate hydrolysis. The conceptual hydrogeological model defines the mountainous area as a recharge zone for groundwater flows circulating through weathered and fractured superior parts of the massif. Local flows contribute to the baseflow of surface streams, while regional flows (medium-distance and long-distance) circulate downstream, towards the southwest, recharging the aquifer system of the Bucaramanga Formation. In the area of the Berlín Páramo another regional flow is proposed downstream, towards the northeast.