Experimental Study On Nonaqueous Phase Liquids Transport In Soils

With the rapid development of industry and the growing serious contamination of groundwater, there has been an explosion of interest on the study of nonaqueous phase liquids (NAPLs) migration and transport in subsurface in the developed countries and areas during the past two decades. But there is some retard on these aspects in our country and only a few reports are seen.As a potential threat to groundwater resources, adequate understanding of the behavior of NAPLs in subsurface is especially important. In this paper, focus on the soil and potential groundwater pollution caused by NAPLs, experimental studies were conducted with two different textural soils and under four bulk densities to systemically study the possible mechanisms controlling NAPLs migration and distribution under the guidance of multiphase theories. Also by adding water from the upper side of soil column, simulating irrigation or rainfall to the soils, we analysis the entrapment problems of NAPLs and potential affective factors. We obtained some important results in our study as following:1. Based on multiphase flow theory and soil water dynamics, experimental studies were performed on the relations of capillary pressure and saturation between every two-phase system of water, PCE and air. For the wetting liquid, the irreducible fluid saturation is dependent on the texture of the soils, finer texture inducing higher irreducible fluid saturation, while the residual saturation of nonwetting fluid is more dependent on the pore structure of the soils.2. Taking clay loam and sandy loam as example, the scaled capillary pressure and effective saturation relation between the two-phase systems of water-air and PCE-air can be well uniformed to one curve in power form by multiplying scaling coefficient to the capillary pressure of PCE-air. When introducing Leverett function, the relation of two-phase Pc~S in the soils with various texture and pore structure can also be scaled to one simple curve and the Pc~S~kr at two phases can be extended to three phases situations. 3. When a certain volume of PCE was released and infiltration ceased in the clay loam and sandy loam, the PCE saturation was fairly uniform and nearly saturated in the upper side of the column and decreased with infiltration depth until the front. The PCE saturation in clay sandy was higher than that in the clay loam at the same bulk density. The Green-Ampt and Kostiakov formula can be introduced to describe the relation of the rate, volume and time during infiltration. The relation of infiltration depth and time can be simulated in power, so dose to the relation of release volume and time.4. With the continuing of distribution of PCE, the PCE saturation profile decrease. The saturation was higher in the middle part of the profile when the distribution time is short, and this phenomenon disappeared with time. The infiltration depth with time can be described in power when the time is relative short and in logarithm when the time is long.5. When water was released to the soil from the upper side of the column, PCE was displaced and promoted to distribution downward more quickly, with only 5-10% PCE entrapped in the soils. These entrapped PCE present as long-term contamination to the soil and groundwater. ...