9:15 AM - 9:30 AM
[SEM14-02] Time-domain induced polarization and complex resistivity surveys in a hydrocarbon-contaminated site, and comparative interpretation
Keywords:oil contamination, biodegradation, induced polarization survey, complex resistivity survey
Even though non-aqueous phase liquid (NAPL) is non-conductive, electrical resistivity of NAPL contaminated zone decreases due to interaction between NAPL and the surrounding environment over time, which mainly caused by chemical weathering of mineral during biodegradation. NAPL-contaminated plume usually locates along the direction of the groundwater flow even though the locations can vary according to the density of NAPL: light or dense one (LNAPL or DNAPL). Based on the electrical characteristics of NAPL, contaminated regions can be effectively delineated through geophysical surveys such as electrical resistivity tomography (ERT) and induced polarization (IP) surveys including time domain (TD) IP and complex resistivity (CR) surveys.
ER, IP and CR surveys were performed on the entire ted bed in the military, located in South Korea, where oil leakages had been suspected from oil tanks and maintenance facilities. In the surveys, we used dipole-dipole arrays with an electrode spacing of 1.5 or 3 m, since the groundwater level is located from 0.3 m to 2.3 m depth and the location of the oil pollution is also expected to be relatively shallow. First, ERT was performed on Sep. 9th, 2021 as a preliminary survey for the secondary geophysical surveys on Oct. 14th-15th, 2021, where ER, IP and CR surveys were conducted to delineate major pollution zones. Since interpretation of data obtained in the secondary surveys showed IP anomalies due to the oil-contaminated area, additional IP and CR surveys were performed to obtain more data for the 3D analysis of the contaminated area.
Obtained survey data were interpreted through 2D or 3D inversion using not only software of DC2DPRO or DC3DPRO but also in-house algorithms based on a finite element method (FEM). Through recovered subsurface images of ER, chargeability and phase, we analyzed and interpreted oil-contaminated distribution. In addition, inverse results of geophysical data were compared with results of soil and ground water analyses on samples obtained from observation wells in the contaminant area. This study is supported by SEM project (No.2018002440005) and the KETEP (No. 20194010201920).
ER, IP and CR surveys were performed on the entire ted bed in the military, located in South Korea, where oil leakages had been suspected from oil tanks and maintenance facilities. In the surveys, we used dipole-dipole arrays with an electrode spacing of 1.5 or 3 m, since the groundwater level is located from 0.3 m to 2.3 m depth and the location of the oil pollution is also expected to be relatively shallow. First, ERT was performed on Sep. 9th, 2021 as a preliminary survey for the secondary geophysical surveys on Oct. 14th-15th, 2021, where ER, IP and CR surveys were conducted to delineate major pollution zones. Since interpretation of data obtained in the secondary surveys showed IP anomalies due to the oil-contaminated area, additional IP and CR surveys were performed to obtain more data for the 3D analysis of the contaminated area.
Obtained survey data were interpreted through 2D or 3D inversion using not only software of DC2DPRO or DC3DPRO but also in-house algorithms based on a finite element method (FEM). Through recovered subsurface images of ER, chargeability and phase, we analyzed and interpreted oil-contaminated distribution. In addition, inverse results of geophysical data were compared with results of soil and ground water analyses on samples obtained from observation wells in the contaminant area. This study is supported by SEM project (No.2018002440005) and the KETEP (No. 20194010201920).