| Geochemical evolution and groundwater flow in a volcanic aquifer in Escuintla, Guatemala was investigated by spring sampling. Inverse modeling suggests that plagioclase feldspar (An60), olivine (Fo), halite and gypsum are reacting with CO2- charged groundwater to produce Ca-montmorillonite and chalcedony and contribute alkalinity, Mg2+, Ca2+ , Na+, and SiO2(aq) to the groundwater. Groundwater flow patterns are discerned from geochemical and isotopic data. In particular, Mg2+ concentrations distinguish shallow/local flow from deep/regional flow and delta13CDIC ratios differentiate springs with a shallow carbon source (soil CO2) from springs with a deeper carbon source (volcanogenic CO2). Variation in groundwater deltaD and delta18O ratios is attributed to recharge elevation and is used in concert with electrical conductivity to distinguish local, intermediate, and regional flow systems. The springs provided sufficient information to develop a three-dimensional conceptual model of groundwater flow. Spring sampling provided a low-budget approach to develop a three-dimensional conceptual model of groundwater flow in the absence of wells and boreholes. |
