LANA Nerina Belen
Hydrochemical processes, variability and natural background levels of Arsenic in groundwater of northeastern Mendoza, Argentina
GOMEZ, M. L.; CANIZO, MARIA BELEN ; LANA, N.B.; ZALAZAR, G.; RODOLFO WUILLOUD; ARAVENA, R.
JOURNAL OF IBERIAN GEOLOGY
Lugar: Madrid; Año: 2018
Northeastern Mendoza is an arid area dominated by stabilized dunes and paleochannels. Groundwater is the main source of water for domestic and subsistence economy. Two types of wells are used for groundwater withdrawal. Wells operated by conventional windmills or pumps (Ws) and local traditional bucket wells operated manually (BWs). These wells are drugged a few cm below the water table, normally with a diameter of 1 m, remain always open and are located near corrals. The aim of this study was to evaluate the processes that control As in groundwater used As drinking water by rural communities. The study approach included an assessment of the natural as background levels and the use of environmental isotopes (δ18O and δ2H) to determine the origin of groundwater and improve the conceptual model for groundwater flow. Significant statistical differences were found between the chemical features of groundwater from Ws and BWs. The conceptual hydrogeologic model supported by isotopic data indicated that groundwater recharge was from the main Mendoza/Tunuyán Rivers in remote areas and that local rainwater recharge is negligible. The isotopic data suggests that a faster groundwater flow recharge could occur without any influence of a previous evaporation process. The natural As background level was 104 µg/L, with a range of between 8.6 and 394 µg/L. The average As concentration in Ws was 114 µg/L. Water from BWs showed higher average As concentration of 235 µg/L with a higher dispersion, high HCO3−, NO3− PO 4 −3 and Cl− concentrations, and the lowest concentrations of O2 with greater turbidity than groundwater from Ws. The increase in As concentrations in groundwater of NE Mendoza is not related to evaporation processes despite arid climatic conditions. According to the oxidizing environment in the aquifer, high pH and very fine sediments, adsorption?desorption processes from solid surfaces were the determining factors for the availability and spatial variability of As in groundwater. Spatial variability was related to type of well rather than to geomorphologic units or to flow direction. The design of bucket wells, near corrals, allows the input of windblown sediments and leachate from livestock units creating point sources of As contamination in water used for human consumption.