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

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.

Isotope signatures and hydrochemistry as tools in assessing groundwater occurrence and dynamics in a coastal arid aquifer

“…Hydrochemical and isotope tracers provide valuable tools for evaluation of groundwater. It is well recognized that major and minor chemical elements may give an insight into water-rock interactions as well as anthropogenic influences affecting the groundwater system as demonstrated in numerous studies (Hem 1989;Mahlknecht et al 2004;Ledesma-Ruiz et al 2015;Cruz-Fuentes et al 2014;Hernández-Antonio et al 2015;Russak et al 2015), while water isotopes may define groundwater recharge areas, mixing and evaporation sources (Edmunds et al 2003;Horst et al 2007;Jiménez-Martínez and Custodio 2008;Mohammed et al 2014;Gonçalvès et al 2015), and radiocarbon isotopes residence times of old groundwater and its distribution (Fontes and Garnier 1979;Clark and Fritz 1997;Edmunds and Smedley 2000;Mahlknecht et al 2006a). More recently, it has been demonstrated that chlorofluorocarbons are useful in evaluating residence times of modern groundwater, mixing patterns and aquifer's vulnerability to contamination (Busenberg and Plummer 1992;Cook et al 1995;Goody et al 2006;Mahlknecht et al 2006b;Horst et al 2008;Darling et al 2012).…”