Laboratory Investigation of LNAPL Migration in Double-Porosity Soil Under Fractured Condition Using Digital Image Analysis

Abstract

The issue of leakage and spillage of light non-aqueous phase liquid (LNAPL) contribute to groundwater contamination, resulting in groundwater pollution and rendering the quality of groundwater unsafe for drinking and agriculture. Therefore, the objective of this study was to investigate LNAPL migration in the double-porosity soil under vibration effect, which has become important for sustainability of groundwater utilization and a comprehensive understanding of the behaviour of liquid migration into the groundwater. A laboratory experiment was conducted to observe the phenomena and characteristics of soil structure, and the pattern of liquid migration in deformable double-porosity by using digital image processing technique. The experiments show that the simulated results were reasonably concise with the visual observations. The gradual increase in vibration table excitation frequency yielded different vibration responses from the respective soils. This indicated that the soil surface acceleration depended significantly on the soil conditions, soil water content, soil structure, and the pattern of soil crack. Faster migration occurred at the cracked soil surface condition compared to other locations on the soil surface that were not cracked. Comparison between soils with 25% and 30% moisture content showed that the downward migration of LNAPL is faster when the soil moisture content is higher. This occurs in soil with higher moisture content due to greater capillary pressure exerted by the liquids and the inter-aggregate pores. This study proved that the digital image processing technique is capable to provide detailed migration flow information to facilitate the researchers to better understand contaminate migration patterns and to ensure sustainability of groundwater resources.