Contaminant migration in unsaturated soil subjected to subfreezing temperatures

Unsaturated illitic soil was subjected to subfreezing temperatures to examine the effect of heat and moisture redistribution on contaminant migration.;Three series of freezing column tests and two series of cyclic freeze-thaw experiments were performed with different liquid supplies: distilled water (pH = 5.8), a municipal waste leachate (pH = 6.9) and a leachate-heavy metal solution (pH = 2.5). Temperature distribution, water content, concentration of exchangeable cations and heavy metals in pore solution were determined in frozen soil as a function of time and space. The differential scanning calorimetry technique was used to calculate the quantity of unfrozen water in the frozen specimens.;It was found that moisture intake and redistribution were closely related to the temperature gradient, the duration of freezing and the type of liquid used. The unfrozen water content, ionic concentration and temperature gradient were the controlling parameters contributing to contaminant transport in frozen soil. The distribution of exchangeable cations changed with the freezing time due to their migration and replaceability. The accumulation of heavy metals in the soil occurred as a result of cation exchange and precipitation mechanisms.