Groundwater flow processes and mixing in active volcanic systems: the case of Guadalajara (Mexico)

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 (δ 2 H, δ 18 O) were used to trace hydrological processes and tritium ( 3 H) 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-HCO 3 -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 HCO 3 , and the presence of minor elements such as Li, Mn and F. It is a mixed-HCO 3 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.

Understanding the dynamics and contamination of an urban aquifer system using groundwater age (14C, 3H, CFCs) and chemistry

“…T = temperature; EC = electrical conductivity; DO = dissolved oxygen; WT = water table. Water samples were classified into four groups according to Hernández‐Antonio et al (), based on multivariate analysis: CG = cold groundwater; PG = polluted groundwater; MG = mixed groundwater; HG = hydrothermal groundwater.…”

“…The Atemajac and Toluquilla Valleys comprising the GMA are bordered by hills, volcanic cones (El Cuatro, San Martín, and El Colli), plateaus (Tonalá), and volcanic calderas (La Primavera), among other features (Sánchez‐Díaz, ). A more detailed description of the tectonic setting is given in Hernández‐Antonio et al ().…”

“…There is compelling evidence that the groundwater below the Guadalajara metropolitan area has been increasingly impaired for drinking water purposes as a consequence of both natural and anthropogenic processes (IMTA, ; SIAPA, ). The magma chamber below La Primavera Caldera generates hydrothermally active systems that are responsible for the vertical upward movement of hydrothermal fluids through faults, which then mix with regional groundwater that may undergo recharge outside of the border of the basin (Hernández‐Antonio et al, ; Sánchez‐Díaz, ). This groundwater circulates through basaltic and andesitic rocks, forming the deeper Atemajac–Toluquilla aquifer unit below the Toluquilla Valley (Figure ).It is characterized by elevated temperatures, salinity, and Cl, Na, and HCO 3 contents, and contains Li, Mn, B, and F. However, exogenic groundwater pollution occurs mainly from the infiltration of runoff and sewage effluents throughout the urban area of Guadalajara, as well as from return flow from agricultural fields in the Toluquilla Valley (Hernández‐Antonio et al, ; SIAPA, ).…”

“…However, relatively little information is available about its hydrogeological settings, well constructions, and water table configuration. Preferential groundwater flow may also account for additional local groundwater discharge (Hernández‐Antonio et al, ). Thus, we propose an appropriate method for evaluating groundwater age distribution in order to evaluate the flow dynamics and contamination in this region.…”

“…This study uses the classification scheme developed by Hernández‐Antonio et al (). Based on groundwater composition and M3 (Laaksoharju, Skårman, Gómez, & Gurban, ), which is a principal component analysis code, groundwater samples were classified into four groups: cold groundwater, hydrothermal groundwater, polluted groundwater, and mixed groundwater.…”