InterPore2026

Micro-scale characterization of the Bauru Aquifer System (Brazil)

19 May 2026, 09:50

1h 30m

Poster Presentation (MS02) Environmental Porous Media: Water, Agriculture, and Remediation Poster

Speaker

Lívia de Almeida Freitas

Description

Nitrate contamination currently represents one of the most persistent and challenging forms of groundwater pollution in world. This insidious problem affects virtually all aquifers in the state of São Paulo (Brazil), which are responsible for the total or partial water supply of approximately 80% of the municipalities. In this context, the Bauru Aquifer System (BAS) stands out as the main and most accessible source of water for the cities of the central-western region of the state and has likewise been affected by nitrate contamination for many years, as documented in several studies (Cagnon & Hirata, 2004; Varnier et al., 2010; Montanheiro & Chang, 2016; Hirata et al., 2020; Pileggi et al., 2021; Barreto et al., 2023). Despite more than two decades of research, a clear and consolidated scientific consensus has yet to be established regarding the predominant mechanisms controlling the dynamics of nitrogen species in groundwater systems, particularly at the pore scale.
To advance the understanding of these processes and support the development of more effective mitigation strategies, this study focuses on the analysis and characterization of the porous medium within BAS rocks, using samples collected from boreholes drilled in a contaminated urban area in the city of Bauru, São Paulo, Brazil. A suite of complementary methods was applied, ranging from traditional techniques such as grain-size analysis and petrographic thin sections, to advanced X-ray computed microtomography (µCT) techniques using a synchrotron source.
The µCT measurements were conducted at the Brazilian Synchrotron Light Laboratory (Campinas, Brazil), where 3D images of 26 samples were acquired, and 17 injection experiments were performed, as illustrated, for example, in Figure 1. These flow experiments configure 4D analyses, as they allow the 3D evaluation of fluid behavior in the porous medium over time, with high spatial and temporal resolution. Data processing included image reconstruction and segmentation pipelines. The latter were adapted according to the sample features, such as image contrast due to mineralogy and porosity type.
The integration of these datasets allowed the discrimination of three lithological formations within the SAB, and their characterization regarding mineralogical composition, textural features, and pore structure, revealing two more permeable units and a basal unit expected to behave as an aquitard. A high degree of pore-structure variability was also observed within the stratigraphic units themselves. The 4D experiments enabled a preliminary the visualization of flow through the different porous media, including the identification of preferential pathways. These images are still under analysis.
The results of this study are expected to significantly advance scientific knowledge regarding the identification of microenvironments that might control the nitrogen behavior in contaminated groundwater systems, promoting an unprecedented integration of physical, geochemical, and microbiological data. Furthermore, this applied knowledge may support the development of more effective, evidence-based public policies aimed at the sustainable management and mitigation of nitrate contamination in urban aquifers in the state of São Paulo, with potential applicability to other regions in Brazil and worldwide.