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El distrito minero El Triunfo-San Antonio, donde se localizan jales mineros con altas concentraciones de elementos potencialmente tóxicos (EPT), se encuentra en la parte alta de la cuenca. El crecimiento demográfico en la ciudad de La Paz ha ejercido presión para la transferencia de agua de esta cuenca, por lo que el objetivo de este trabajo fue caracterizar la composición hidrogeoquímica del agua subterránea y evaluar su calidad para consumo humano. En 2015, durante las épocas de estiaje (abril-mayo) y lluvias (noviembre-diciembre),

The physicochemical and isotopic characteristics of groundwater and dissolved gas of central Mexico provide valuable information about the geologic and tectonic context of the area. Low–high-enthalpy manifestations (up to 98 °C in springs and more than 100 °C in geothermal wells) are distributed within the San Juan del Río, Querétaro, and Celaya hydrologic basins, located at the boundary between the current Mexican magmatic arc and an extensional continental area with intraplate volcanism called Mesa Central Province. Groundwaters in the study area represent a mixture between the cold water end-member with a Ca2+-Mg2+-HCO3- composition and a hydrothermal end-member enriched in Na+, K+, SO2−, and Cl-. Cold and hot groundwaters δ2H and δ18O plot along the same evaporation lines and do not exhibit a magmatic input. Dissolved and free gas do not show a typical volcanic composition signature. He and Ne isotope composition provide evidence of an important contribution of non-atmospheric noble gases. Although helium composition mainly has a crustal origin (21–83%), the mantellic contribution (1–39%) is higher than expected for an area lacking recent volcanism. A volatile-rich magma aging at depth was discarded as the source of this mantellic helium signature but points out a recent mantellic contribution. Thus, we propose that mantellic helium comes from the sublithospheric mantle into the shallow crust through the highly permeable tectonic boundaries between the geologic provinces, namely the N−S Taxco−San Miguel de Allende and Chapala-Tula fault systems. Mantellic helium flow rates through these fault systems were estimated to have values ranging from 0.1 m/yr to 2.9 m/yr. This He flux range implies that aside from subduction, mantle volatile degassing enhanced by crustal fault systems is the main degassing process in the region studied.