Salinization in the Hueco Bolson Aquifer near the Rio Grande, El Paso, Texas

Groundwater to a depth of 300 m beneath the Rio Grande in the El Paso-Ciudad Juárez area exhibits complex isotope and salinity stratification.   Post-dam (post –1916, type A) river water has infiltrated to depths up to 80 m.  Pre-dam (type B) river water has infiltrated to 300 m depth near downtown El Paso, and has mixed with, or been displaced by, high-salinity native Hueco Bolson groundwater (type C) further downstream.  Salinity and isotope boundaries do not correspond precisely.   Basin fill more than 5 km north of the Rio Grande contains only type C water.  Isotope stratification in that area corresponds to water residence time and to degree of evaporation; highest salinities are associated with the most evaporated water.   Modeling of water budgets for the basin fill beneath the river predicts the mixing of water types B and C where changing rates of pumping have caused a reversal of groundwater flow direction between El Paso and Ciudad Juárez.   Unmixed type B water infiltrates to greater depth beneath downtown El Paso than is predicted by the model for current conditions.