Mapping groundwater contamination risk in a periurban watershed in northeast Brazil

Abstract

Groundwater is the most readily available source of fresh water worldwide and plays a crucial role in different human activities, but faces increasing threats due to overexploitation, contamination and effects of climate change. In Brazilian cities such as Natal, capital of Rio Grande do Norte state (RN), the growing demand for this resource in response to rapid urban growth and increasing water supply needs highlights the importance of integrated management and pollution control strategies. This study adopted an integrated approach within a Geographic Information System (GIS) environment, using primary and secondary spatial data, and applied Multi-Criteria Decision Analysis (MCDA) to assess the intrinsic vulnerability and contamination risk of aquifers in the Doce River Basin (DRB), in the metropolitan area of Natal (RN). The methodology involved assigning weights and scores to natural attributes, well density and land use and land cover. The analysis considered the potential risk of contamination by any type of contaminating agent, including nutrients, organic compounds, and other anthropogenic pollutants commonly associated with urban land use. The results revealed moderate to high vulnerability and contamination risk in over 90 and 80 % of the DRB, respectively. Low average rainfall, sandy soils, and shallow or highly permeable aquifers, combined with intensive human activities significantly exacerbate the risk of groundwater degradation. Urban areas on sedimentary terrain and unconfined, porous and fractured aquifers are particularly critical.