Spatiotemporal variability of underground waters inappropriate for the human consumption: Concentrations of barium, total chromium and vanadium

Abstract

Among the parameters of water quality can be highlighted Barium, Total Chromium and Vanadium, due to the possible harmful effects on human health. Data from the Environmental Company of São Paulo State have pointed to wells at the Bauru Aquifer System (BAS) with concentrations of these elements above of the maximum permissible values (MPV). This work aims to characterize the spatial and temporal variability of waters unfit for human consumption in the BAS as a function of the concentrations of Barium, Total Chromium and Vanadium. The triennial groundwater quality data (2013-2015) were used, considering 74 (in 2013), 82 (in 2014) and 88 (in 2015) monitoring wells at BAS. The descriptive statistical analysis was performed and the spatial dependence was evaluated through the experimental variogram. The integration of the kriging maps was done through simple map algebra operations. The descriptive analysis indicated that all parameters/ periods studied presented occurrences of values above the MPV. The most critical situations were for Total Chromium that presented between 11-16 wells with values above 50 μg L-1 and Vanadium which presented between 4-7 wells with values above 50 μg L-1. It was verified the spatial dependence for all parameters studied, whose variograms adjustments presented R2 between 0.707 to 0.966 and cross-validation correlation coefficient (r) ranging from 0.606 to 0.902, indicating appreciable estimation maps by kriging. The ranges varied from 52.6-79.5 km (Barium), 81.0-120.3 km (Total Chromium), and 44.6-55.7 km (Vanadium). The area of greatest attention is in the Presidente Prudente region, with estimates above the MPV combined for Total Chromium and Vanadium. The results deserve attention from the responsible authorities, mainly due to the fact that there are numerous private wells in these areas.