Applying FDEM, ERT and GPR at a site with soil contamination: A case study

Highlight
• Study of applications of GPR, ERT and FDEM on the pre- and post remediation investigations at a soil contaminated site
• In pre-remediation investigation GPR signals were severely attenuated by the sludge.
• ERT pre-remediation investigation suggested the completeness of the USTs with sludge inside.
• FDEM pre-remediation investigation defined the contamination distribution.
• Using GPR, ERT and FDEM in post-remediation investigation can indirectly verify the accomplishment of remediation work.

This study employed the combination of three methods, namely the Frequency Domain Electromagnetic (FDEM), Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) to evaluate a heavy-metal contaminated site for both pre- and post-remediation investigations. The main goals were to verify the position and the integrity of the underground storage tanks (UST), and to determine the effectiveness of remediation to ensure no contaminants remained at the site. In general, the GPR survey was effective at locating shallowly buried objects. However, due to the highly conductive nature of the heavy-metal laden sludge, the GPR signals were attenuated severely. Thus, the first attempt to use GPR in the pre-remediation investigation did not achieve the desired results and other methods were deployed. The existence of the UST and the sludge within were confirmed by ERT and the UST shape was mapped by FDEM. The principal remediation scheme was soil replacement by replacing the contaminated soil with clean silt. Based on the distinctive property differences of the contaminated soil and the clean silt, the completion of the remediation was confirmed by the differences between pre-remediation and post-remediation in GPR, ERT and FDEM results.