Regional groundwater flow and geochemical evolution in the Amacuzac River Basin, Mexico

Morales-Casique, Eric; Guinzberg-Belmont, Jacobo; Ortega-Guerrero, Adrián

Regional groundwater flow and geochemical evolution in the Amacuzac River Basin, Mexico | Ecoulement régional des eaux souterraines et évolution géochimique dans le bassin versant de la rivière Amacuzac, Mexique Flujo regional de agua subterránea y evolución geoquímica en la cuenca del río Amacuzac, México 墨西哥Amacuzac河流域区域地下水流和地球化学演化 Fluxo regional de águas subterrâneas e evolução geoquímica na Bacia do Rio Amacuzac, México

2016

Morales-Casique, Eric | Guinzberg-Belmont, Jacobo | Ortega-Guerrero, Adrián

An approach is presented to investigate the regional evolution of groundwater in the basin of the Amacuzac River in Central Mexico. The approach is based on groundwater flow cross-sectional modeling in combination with major ion chemistry and geochemical modeling, complemented with principal component and cluster analyses. The hydrogeologic units composing the basin, which combine aquifers and aquitards both in granular, fractured and karstic rocks, were represented in sections parallel to the regional groundwater flow. Steady-state cross-section numerical simulations aided in the conceptualization of the groundwater flow system through the basin and permitted estimation of bulk hydraulic conductivity values, recharge rates and residence times. Forty-five water locations (springs, groundwater wells and rivers) were sampled throughout the basin for chemical analysis of major ions. The modeled gravity-driven groundwater flow system satisfactorily reproduced field observations, whereas the main geochemical processes of groundwater in the basin are associated to the order and reactions in which the igneous and sedimentary rocks are encountered along the groundwater flow. Recharge water in the volcanic and volcano-sedimentary aquifers increases the concentration of HCO₃ –, Mg²⁺ and Ca²⁺ from dissolution of plagioclase and olivine. Deeper groundwater flow encounters carbonate rocks, under closed CO₂ conditions, and dissolves calcite and dolomite. When groundwater encounters gypsum lenses in the shallow Balsas Group or the deeper Huitzuco anhydrite, gypsum dissolution produces proportional increased concentration of Ca²⁺ and SO₄ ²–; two samples reflected the influence of hydrothermal fluids and probably halite dissolution. These geochemical trends are consistent with the principal component and cluster analyses.

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