Evaluating the reliability of geophysical methods for investigating the migration of a hydrocarbon plume: validation by sample analysis

Abstract

Geophysical methods are extensively used to assess contaminated sites. However, the validation of geophysical exploration results remains crucial for practical applications of these methods. In this study, Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) were used to investigate an abandoned hydrocarbon-contaminated site in Jiangsu, China. Dense survey lines were drawn across the contaminated site to generate continuous monitoring data. In addition, 20 boreholes were strategically drilled at identified anomalous points using geophysical methods. Multiple groundwater samples were analyzed from these boreholes and analyzed hydrocarbon concentrations. The obtained geophysical data were compared with groundwater data to assess the hydrocarbon extent and degree at the study site, as well as to evaluate the reliability of the geophysical survey results. The results demonstrated the effectiveness of continuous resistivity profiles in mapping the contaminant plume, showing consistent contaminant migration directions with the groundwater flow. The contaminant plume patterns obtained by interpolating groundwater sample contaminant concentrations were in line with the resistivity profiles. Groundwater samples from boreholes in high-resistivity zones exhibited higher hydrocarbon concentrations than corresponding regulatory limits. On the other hand, GPR successfully identified enhanced reflective signals associated with the presence of hydrocarbons, necessitating comprehensive interpretations that integrate these findings with resistivity results. The analysis results of unsatisfactory geophysical data in relation to the specific site conditions indicated that soil layer heterogeneity was the main source of anomalous electrical responses. This study validated the accuracy and efficiency of geophysical methods in investigating the migration of hydrocarbon plumes and assessing their contamination levels in groundwater.