Assessing Groundwater Contamination Using Geophysical Methods in Urban Areas

Thesis Abstract

Groundwater contamination in urban environments poses a significant threat to public health, ecological stability, and sustainable water resource management, particularly in rapidly expanding cities where anthropogenic activities often outpace regulatory oversight. This study aims to assess the extent and spatial distribution of groundwater contamination in urban areas through the application of advanced geophysical methods, providing empirical data to inform sustainable urban water management strategies. The specific objectives include (1) identifying the key geophysical signatures associated with different types of groundwater contaminants, (2) mapping the spatial variability of aquifer properties and pollution levels, (3) correlating geophysical data with existing hydrochemical analyses, and (4) evaluating the efficacy of specific geophysical techniques in detecting subsurface contamination. The research adopts a mixed-methods approach, integrating quantitative geophysical surveys with qualitative spatial analysis. The study area comprises a metropolitan urban district with a documented history of groundwater pollution due to industrial effluents, inadequate waste disposal, and urban runoff. The population involved includes borehole well surveys and existing hydrochemical datasets from approximately 150 groundwater sampling points within the study region. A stratified random sampling method was employed to select 30 representative boreholes for geophysical investigation, ensuring coverage across varying land use zones, proximity to pollution sources, and aquifer types. Data collection employed multiple geophysical techniques, including electrical resistivity tomography (ERT), ground-penetrating radar (GPR), and electromagnetic induction (EMI), to capture comprehensive subsurface properties. These instruments were calibrated and validated through pilot surveys and laboratory testing of soil and water samples. Hydrochemical data, including measurements of nitrate, heavy metals, pH, and electrical conductivity, were collected concurrently and analyzed using ion chromatography, atomic absorption spectroscopy (AAS), and pH meters. The geophysical data were processed using inverse modeling techniques, with resistivity data analyzed via 2D and 3D imaging to delineate pollution plumes, aquifer boundaries, and zones of altered conductivity. Spatial statistical analysis, including regression analysis and analysis of variance (ANOVA), examined relationships between geophysical responses and hydrochemical indicators. Expected findings include the identification of distinct geophysical anomalies corresponding with contaminated zones, allowing for the delineation of pollution extent and depth. It is anticipated that resistivity contrasts and electromagnetic signatures will correlate strongly with areas exhibiting high nitrate and heavy metal concentrations, confirming the utility of geophysical methods as proxies for groundwater quality assessment. The integration of geophysical and hydrochemical data is expected to enhance the spatial resolution of contamination mapping and provide a cost-effective alternative to extensive sampling campaigns. This study contributes to the existing body of knowledge by demonstrating the applicability of integrated geophysical techniques in urban hydrogeological investigations, specifically for contamination assessment. It extends theoretical understanding of the relationship between subsurface electrical properties and pollutant distribution, grounded in theories of geoelectrical response and hydrogeological heterogeneity. The findings underscore the potential for non-invasive, rapid assessment of complex contamination scenarios, particularly in densely built environments where traditional sampling is challenging. The study concludes with recommendations for adopting geophysical surveys in routine groundwater monitoring programs, emphasizing their role in early detection and spatial delineation of contamination zones. It advocates for the development of integrated monitoring frameworks combining geophysical data with hydrochemical analyses to optimize resource allocation, improve risk assessment, and support regulatory enforcement. Future research should explore the application of emerging geophysical technologies such as induced polarization (IP) and spectral induced polarization (SIP) in urban groundwater contamination studies, alongside longitudinal monitoring to track pollution dynamics over time.