Transport and fate of volatile organic chemicals in unsaturated, nonisothermal, salty porous media: 2. Experimental and numerical studies for benzene

Abstract

Simultaneous transport in soil of heat, water, potassium chloride, and benzene was studied experimentally and numerically. A laboratory experiment permitted observation of temperature, water content, chloride concentration and benzene concentration distributions in soil. A numerical model based upon newly developed transport theory was used to simulate the observed data. Transport of benzene in soils was simulated numerically under isothermal and nonisothermal conditions. Simulated results for benzene were compared with experimental data. Experiments were conducted in sealed aluminum columns (0.05-m I.D. and 0.20-m length) with sterilized salinized unsaturated Fayette soil. The soil had initial water content of 0.22 m 3/m 3 and initial inorganic solute concentration of 0.20 mol/kg. Benzene was injected at one end of each soil column (top end) to provide 143 g/m 3 benzene in the upper 0.01 m portion. The isothermal soil columns were set in an incubator at 29°C. The nonisothermal experiment had upper and lower boundary temperatures of 34 and 21°C, respectively. Isothermal and nonisothermal experiments each lasted for seven days. A numerical model based upon heat and mass transfer theory was used to predict transient soil temperature, water content, and inorganic and organic chemical distributions. Both predicted and measured final temperatures showed linear distributions. In the nonisothermal study, water moved from the hot region toward the cold region, and inorganic solute accumulated in the hot region. Benzene redistributed along the soil column for both isothermal and nonisothermal conditions. Total concentration of benzene in the cold region under nonisothermal conditions was larger than the concentration of benzene in the hot region. On the other hand, the concentration of total benzene was approximately uniform along the soil column under isothermal conditions. For isothermal conditions, the benzene concentration by volume in the three phases followed the order: liquid>solid>gas. The results of this study indicated that transport models need to include the effect of temperature and temperature gradient to describe the movement of volatile chemicals in soils.