Hydrogeology of the Villafáfila lakes (Zamora, Spain) and their relationships with regional flow

Villafáfila lakes locates in the valley of the Salado river (Zamora, Spain) which develops on Cenozoic sedimentary rocks of the Duero basin. The lakes are 10 to 20 cm depth and commonly become dried out during the summer. Lake mean temperature is 11.8ºC during the winter and 19.4ºC during the summer and the electric conductivity varies from 4000-5000 μS/cm respectively. Calciummagnesium bicarbonate waters with low salinities (400 mg/l of TDS) have been identified in wells located in the surrounding hills. At the toe of the hills dominate sodium bicarbonate-chloride waters with salinities about 900-1300 mg/l of TDS. Sodium chloride waters with salinities about 2500-3250 mg/l occur in deep wells (depths > 40 m), lakes and in the springs surrounding the lakes. During the summer the groundwaters below the dried out lakes reaches electric conductivities about 19000 μS/cm, and halite efflorescences occur in the lake plains. Villafáfila lakes are close to the western margin of the Duero and regional piezometry shows that groundwater flow comes from the northeastern part of basin and further away from the Cantabrian mountains in Palencia province, 150-200 km away from Villafáfila. Wells opened at different depths in the same aquifer suggest that there is a vertical ascendant component in the groundwater flow. Sodium chloride waters from deep wells are considered the regional flow that discharge in the Villafáfila area. The oxygen and hydrogen isotopes evidence that these groundwaters were precipitated in an elevated mountain area. The detrital character of the northern part of the Duero basin and the apparent lack of evaporites in this area points towards a solute adquisition in the catchment of the Cantabrian mountains where Triassic evaporites crops out. The proximity of elevated blocks constituted by low permeability metamorphic rocks are responsible of the groundwaters upwelling in the Villafáfila área.