- Departamento de Dinámica Terrestre Superficial, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, ZIP: 04510, Ciudad de México, México (lcjose@geologia.unam.mx)
In Mexico City, where population growth has significantly increased water demand, a well was drilled to a vertical depth of 1992 meters.
To understand the groundwater dynamic in the critical zone- an area extending from the surface to the base of the groundwater system, where complex interactions occur between the atmosphere, lithosphere, hydrosphere, and biosphere- various tools were employed, including geophysical log analysis, pumping tests, and groundwater sampling for hydrochemical and isotopic (stable and radioactive) analyses.
The results revealed consistent ion concentrations during hydrogeochemical monitoring, classifying the water as sodium-chloride type with minor nitrate contamination attributed to the use of drilling mud.
Isotopic analysis indicated that the water likely originated from precipitation infiltrating at approximately 3000 meters above sea level, possibly from nearby mountain ranges. Radiocarbon dating estimated a residence time of 2840 years, although additional testing is necessary for confirmation.
Hydraulic tests determined a transmissivity of 768 m²/day and a specific storage of 3.11 × 10⁻⁶ m⁻¹, corresponding to an average hydraulic conductivity of 0.885 m/day. This is a complex hydrogeological system characterized by deep, highly fractured saturated zones. Groundwater in this well originates from the deep infiltration of rainfall in the surrounding sierras, circulating through fractures in volcanic rocks. Initially, the water quality showed temporary mixing with surface water due to the interaction between formation water and drilling mud; however, it later exhibited a distinct chemical composition.
The residence time of the water indicates a dynamic system with varying water ages. The results suggest hydraulic connectivity between different hydrogeological units and an endorheic behavior of groundwater flow in the area. In summary, this study enhances the understanding of groundwater flows in Mexico City, emphasizing the critical zone's role in shaping subsurface processes and highlighting the importance of considering the complexity of these systems for sustainable management.
How to cite: Martínez Casas, Z., Morales Casique, E., Olea Olea, S., and Lezama Campos, J. L.: Deep flow behavior and the critical zone in a deep well: A hydrogeological study in Mexico City, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12792, https://doi.org/10.5194/egusphere-egu25-12792, 2025.
