Water-rock interaction processes in springs and wells of the Mexico City groundwater flow system

The Mexico City region is a densely populated region in the world and has problems in guaranteeing the supply of drinking water to its inhabitants. Its groundwater flow system is subject to intensive exploitation. The water in the city is coming from a lot of sources as wells located in the city and springs in the ranges. The geology in the basin is mainly in lacustrine sediments; volcanic rocks shallow and deep and carbonate rocks in the depths.

We collected water table values, major ions, and trace elements compositions from other research: wells (1999) and springs (2015) to investigate hydrogeochemical processes as well as to understand the hydrodynamics of groundwater and their chemical differences between ranges and plains. The groundwater chemical composition is related to the water-rock interaction processes.

We applied two inverse model sections (PHREEQC code) in springs and wells. The inverse model section in the springs showed the dissolution of gypsum, biotite, SiO₂ (aqueous), volcanic glass, labradorite, chloride, and precipitation of amphibole, kaolinite, and H₂O (gaseous). Whereas the inverse section model in wells presents the dissolution of CO₂ (gaseous), gypsum, biotite, volcanic glass, halite, plagioclase, olivine, and precipitation of kaolinite and pyroxene.

Understanding the hydrochemical mechanisms of water-rock interactions eventually leads to the development of appropriate strategies for sustainable groundwater management.