Abstract
Abstract. Groundwater chemistry and isotopic data from 40 production wells in the Atemajac and Toluquilla valleys, located in and around the Guadalajara metropolitan area, were determined to develop a conceptual model of groundwater flow processes and mixing. Stable water isotopes (δ2H, δ18O) were used to trace hydrological processes and tritium (3H) to evaluate the relative contribution of modern water in samples. Multivariate analysis including cluster analysis and principal component analysis were used to elucidate distribution patterns of constituents and factors controlling groundwater chemistry. Based on this analysis, groundwater was classified into four groups: cold groundwater, hydrothermal groundwater, polluted groundwater and mixed groundwater. Cold groundwater is characterized by low temperature, salinity, and Cl and Na concentrations and is predominantly of Na-HCO3-type. It originates as recharge at "La Primavera" caldera and is found predominantly in wells in the upper Atemajac Valley. Hydrothermal groundwater is characterized by high salinity, temperature, Cl, Na and HCO3, and the presence of minor elements such as Li, Mn and F. It is a mixed-HCO3 type found in wells from Toluquilla Valley and represents regional flow circulation through basaltic and andesitic rocks. Polluted groundwater is characterized by elevated nitrate and sulfate concentrations and is usually derived from urban water cycling and subordinately from agricultural return flow. Mixed groundwaters between cold and hydrothermal components are predominantly found in the lower Atemajac Valley. Twenty-seven groundwater samples contain at least a small fraction of modern water. The application of a multivariate mixing model allowed the mixing proportions of hydrothermal fluids, polluted waters and cold groundwater in sampled water to be evaluated. This study will help local water authorities to identify and dimension groundwater contamination, and act accordingly. It may be broadly applicable to other active volcanic systems on Earth.
Highlights
Active volcanic systems are frequently accompanied by an intense hydrothermal circulation, which is controlled by the exchange of mass and energy between groundwater systems, magmatic fluids and hot rock (Goff and Janik, 2000; Di Napoli et al, 2009)
The initial classification of groundwater groups by cluster analysis has been confirmed by water isotopic technologies, and identifying the controlling factors by principle component analysis is consistent with M3 modeling
A conceptual flow model was constructed for the Atemajac–Toluquilla aquifer system
Summary
Active volcanic systems are frequently accompanied by an intense hydrothermal circulation, which is controlled by the exchange of mass and energy between groundwater systems, magmatic fluids and hot rock (Goff and Janik, 2000; Di Napoli et al, 2009). The chemical characterization of fluids and groundwater has been used as an indicator of the subsurface structure and the origin of released fluids when hydrogeological information is scarce (Henley and Ellis, 1983; Appelo and Postma, 2005) Hydrochemical data, such as high electrical conductivity (EC), high temperatures and elevated concentrations of As, B, Br, Cl, Cs, F, Fe, Ge, I, Li, Mn, Mo, Na, Rb, Sb, Ta, U and W denote the presence of hydrothermal fluids in groundwater (Reimann et al, 2003; Dogdu and Bayari, 2005; Aksoy et al, 2009).
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