Avaliação do impacto de recarga variável no Aquífero Barreiras em Natal-RN, associado com a urbanização e ampliação da rede de coleta de efluentes sanitários

Abstract

The recharge of unconfined urban aquifers is substantially affected by high rates of soil sealing, while, occasionally, it may present additional components to those from rainwater infiltration. In this case, infiltrations caused by leaks in sewage and water supply networks can represent significant contributions to these recharge rates. This situation is common in some areas of Northeast Brazil, especially in places with high population density and deficiencies in wastewater collection and supply networks. In this last aspect, it is not uncommon to have the contamination of urban aquifers by nitrate resulting from the infiltration of untreated wastewater. This research aimed to evaluate the effects of a variable recharge resulting from land use and occupation, as well as artificial contributions, in the Aquífero Barreiras, of a predominantly unconfined hydraulic character, in the city of Natal-RN. Additionally, we conducted simulations about the prospects of natural purification of waters with high nitrate contents, previously characterised by different renewal times associated with the changes in saturated zones due to decreases in recharge rates. The methodology used was based on the elaboration of numerical models and scenario analysis, emphasising the variations of artificial recharges resulting from wastewater infiltration and losses by the public supply network. Thus, the total recharge rates were calculated by individualizing areas with higher and lower population density, with subsequent simulations of different natural and artificial contributions. The results demonstrate significant variations in the potentiometric surface of up to 15 meters in several areas presented in the critical scenario, which considered the removal of artificial recharge and inversions of the groundwater flow. In this context, the saturated zones showed a variation of about 44 million m3 between the current and critical scenarios, associated with the suppression of 100% of the contribution from losses by the supply network and wastewater infiltration. In terms of prospects for natural purification of waters with high nitrate contents, from the analysis of renewal times and based on the variations of saturated zones calculated in the numerical models, values ranging from 6.5 to 12.9 years were obtained, this time being longer considering the most critical scenario reported in terms of recharge. The results presented here may contribute to the management of shallow aquifers in similar scenarios, especially regarding urbanization rates and efficiency in supply and sewage networks.