Geochemical Assessment of Groundwater in the Peri-urban Environment of Buenos Aires, Argentina

Abstract:

Groundwater pollution is a major concern in peri-urban environments. Thus, water quality is being investigated at several domestic wells in Brandsen, 70 km south of Buenos Aires, Argentina. To present, about 20 water sources were sampled in orchards and small farms of the area. There is limited data about the wells construction, although collected information suggests that groundwater is derived from the superficial sandy loams of the Pampean Aquifer. Samples were analysed for major inorganic elements using ion chromatography and ICP-MS. Titration was used to estimate alkalinity. Physical characteristics (EC, pH, temperature) were measured on site. Results show that groundwater pH ranges from 6.5 to 7.8, with a specific conductance of 180 to 255 mS/m. A peak of 360 mS/m in one horticultural parcel is associated to local NO₃^- concentrations up to 140 mg/L. This value exceeds the maximum recommendations set by the WHO (50 mg/L). Considering that fertilizer inputs in that property are negligible, the high levels of NO₃^- might be attributed to effluents from a neighbour septic tank. An increase in NO₃^- (>150mg/L) was also detected in two conventional farms. This increase correlates to elevated SO₄^2- concentrations (>300 mg/L) suggesting thus, fertilizers percolation into the saturated zone. The leaching of these fluids might be exacerbated by irrigation during new planting, and accumulations of fertilizer-solids in the root zones from previous seasons. Chloride concentrations average ~90 mg/L and would not pose a threat to health at the moment. Its main origin would be related to connate waters in the loam matrix, although some anthropogenic inputs might occur in the previously described farms. In general, the rest of the analysed elements fall within acceptable levels for drinking purposes as well. Nevertheless, further work is still necessary to better define the fate of the potential harmful elements and assess seasonal variations in water quality.