Case study of ground penetration radar (GPR) to assess lead migration

Abstract

This paper describes research to characterize subsurface contamination caused by leaching of lead (Pb) from batteries disposed of at the surface, which has spread with groundwater movement. The contaminated soils and aquifer are located in the Matano formation (Sulawesi, Indonesia). Ground Penetrating Radar (GPR) was used to detect and delineate Pb-contaminated soils (i.e., solid-phase Pb). Lead in the solid and aqueous phase have different characteristics and responses when subjected to electromagnetic (EM) waves. Many studies have used GPR to map solid-phase Pb contamination in the subsurface. GPR uses EM as the base medium to receive subsurface images and is useful for the detection of solid-phase Pb contamination but cannot detect aqueous-phase Pb. The first step in the remediation process was to delineate solid-phase Pb contamination in the subsurface using GPR, which required a geotechnical survey to support GPR. Samples of soil and aquifer solids were then taken to quantify lead concentrations using X-ray fluorescence (XRF). We collected 15 lines of GPR measurements and 11 soil samples to quantify Pb. Frequencies of 600 MHz and 900 MHz were used for the GPR antenna. The results identified a clay layer at a depth of between 3 m and 4 m, which appears to have served as barrier to downward migration of Pb-contaminated groundwater. A shadow zone and low reflectance in the GPR subsurface section images were used to identify as the Pb contamination, which has a distinct wavelength ranging between 0.36 m and 0.45 m. We conclude from the results of this study that GPR was an effective tool for the delineation of the vertical and horizontal spread of Pb contamination eastward from the source.