Time-lapse electrical resistivity tomography (ERT) monitoring of used engine oil contamination in laboratory setting

Abstract

Geophysical methods are being used effectively for monitoring, characterizing, and mapping Light Non-Aqueous Phase Liquids (LNAPLs). Although Used Engine Oil (UEO) is one of the most common LNAPLs contaminants within the urban communities, not much attention has been given for the geophysical study of UEO contamination. The main objectives of this research were to monitor the migration of UEO, and to investigate the electrical characteristics of UEO as viscous LNAPL within a tank aquifer system using time-lapse electrical resistivity tomography (ERT). The ERT data were collected using 24 electrodes arranged as a miniature resistivity array. The contaminant was injected into the tank aquifer system, and the electrical changes of the contaminant were monitored for a period of 80 days. The time lapse results revealed vertical and lateral migration of the contaminant with the lateral migration dominating. The results also revealed increase in electrical resistivity values from day 1 until day 35, then a drastic decrease to day 50, then a slight increase to day 60, and then decrease till day 80. Based on the change of odour of the contaminated region from used engine oil odour to slightly rotten odour and based on relevant published research, it was interpreted that the decrease in electrical resistivity was associated with UEO degradation that might be caused by microbial activity. The results of this study show that time-lapse ERT is an effective geophysical method to monitor used engine oil contamination.