Retention and transport of a hydrocarbon in a silt

The paper presents an experimental investigation of the retention and transport properties of a light hydrocarbon pollutant (Soltrol) in unsaturated compacted samples of a low-plasticity Jossigny silt. Based on the work of Busby et al. and Steffy et al., a special multiphase cell was developed that allowed for the independent control of oil, water and air pressures. Oil retention curves of samples compacted at various densities and water contents were determined, together with oil permeability calculated using the methods of Gardner and Kunze & Kirkham. Microstructure investigations based on mercury intrusion porosimetry were conducted to help interpret the results. It was observed that the initial water degree of saturation of the soil conditioned the extent of oil infiltration. In the samples studied, the intra-aggregate pores were saturated with water, and oil infiltration affected only the inter-aggregate pores. For very loose samples, although some physico-chemical interactions were suspected between oil and soil, oil/air capillary action appeared to be the dominant phenomenon influencing oil retention and transport. In most samples, a 25 kPa oil suction allowed for the draining of a significant quantity of oil. The experimental results from this study help in better understanding the fundamentals of oil pollutant transport and decontamination mechanisms in oil-polluted soil.