Abstract
Phreatic aquifers are a strategic source of water for various activities and human consumption around the world. In addition, they are essential systems in the regulation of the hydrological cycle and all the resulting ecosystem processes, especially in tropical humid regions. These aquifers may be vulnerable to pollution, overexploitation and salt water intrusion. This thesis seeks to understand the functioning and dynamics of a heterogeneous phreatic aquifer, based on its hydrodynamic behavior, hydrogeochemical processes and transit and residence times of groundwater. The case study corresponds to the groundwater aquifer in the Gulf of Urabá, Colombia.The results of the thesis show that the groundwater aquifer presents an important recharge and a direct relationship between the piezometric levels and the precipitation at the beginning of the direction of the groundwater flow. As groundwater flow advances, the piezometric response pattern suggests additional flows to precipitation infiltration, such as groundwater drainage, tidal oscillation, and possible surface flow inputs.The hydrogeochemical composition of groundwater is mainly governed by the contact of water and soil with CO2 (g), which induces silicate weathering, resulting in HCO3--Ca2+-Mg2+ facies.The isotopic composition of groundwater with an average δ18O of -6.16 ‰ is consistent with the isotopic composition of precipitation, which confirms the direct recharge of precipitation. Different tracers such as 3H, 14C and CFC’s validated the infiltration of rainwater into the aquifer and a mixture of younger waters (0 years) with relatively older waters (more than 40 years), in accordance with the estimated renewal rate according to hydrodynamics.The integrated information from the partial results allowed the development of a conceptual hydrogeological model representing the functioning of the aquifer.