Spatial and temporal evolution of nitrate contamination in the urban aquifer of Urânia (SP)

Abstract

Located over the Adamantina Aquifer domains (Bauru Aquifer System), the city of Urânia/SP is significantly contaminated with nitrate (NO₃^-) via urbanization process, initially without sewage system installation in the 1960s. This study aims to evaluate the evolution of this contamination in time and space, based on chemical analysis of 13 sampling campaigns in the last 20 years. Chemical data were compiled and well groups were selected, as well as new water samplings, to search for nitrate concentration patterns in distinct regions of the city. It was concluded that the highest degree of contamination is historically in the shallow portion of the aquifer, near the Comprido stream and in the northwest region of the city (>150 and 100 mg/L NO₃^-, respectively). This is due to the high density of previously existing cesspits (48 cesspit/km² and 23 cesspit/km², respectively) and, in the case of the northwest area, due to the older urban occupation and leaks of a sewage network installed in 1977 and without maintenance. These two areas also showed high concentrations of nitrate (50 to 100 mg/L NO₃^-) in the intermediate portion of the aquifer, indicating contamination reaching greater depths. The southern portion of the city is historically the least contaminated due to late urbanization, in part concomitant with the arrival of the sewage system (in 1985), as well as the lower density of cesspits (17 cesspit/km²), presenting in most analyzes values of nitrate up to 50 mg/L NO₃^-.