A ocorrência de nitrato e sua perspectiva de depuração no cenário de um aquífero não confinado urbano com recarga variável, nordeste do Brasil.

The occurrence of nitrate and its depuration perspective in the scenario of an urban unconfined aquifer with variable recharge, northeastern Brazil.

Abstract

The nitrification of groundwater in urban areas commonly stems from the infiltration of untreated wastewater. This study aimed to characterize the presence of NO-3 and evaluate the possibilities for natural remediation in an urban unconfined aquifer subject to variable recharge. The investigation utilized hydrochemical analysis techniques and numerical modeling to examine the interplay between aquifer thickness variations, recharge fluctuations, urban development, and the configuration of the sanitary sewage system. Four scenarios were devised to assess the decline in saturation levels and its subsequent impact on the aquifer's theoretical replenishment rates, assuming a gradual reduction in nitrogen inputs from infiltrating waters. Over the years 2012 to 2020, findings revealed a steady escalation in nitrate concentrations in approximately 58% of the observed wells, with concentrations trending higher towards the southern reaches of the study area. The estimated residence times, indicative of the potential for water quality restoration, spanned from 6.5 to 12.9 years, with the latter value representing the most critical scenario in terms of recharge dynamics. In this critical scenario, all contributions from losses via the water supply network and wastewater infiltration were assumed to be eliminated.