The change in capillary moisture capacity of gray forest soil was analyzed at various levels of oil and diesel fuel contamination (50, 150 and 300 ml/kg), as well as as a result of reagent treatment of contaminated soil samples using the nonionic surfactant Tween-80. The concentration of Tween-80 in the wash solutions was 1, 5 and 10 g/L. The ratio of the system components was: 100 g of soil: 400 ml of water: 100 ml of washing solution. Treatment of oil-contaminated soil with washing solutions was carried out for 1 hour with continuous stirring (60 rpm) and a temperature of 20 °C. Contamination of gray forest soils with oil and diesel fuel has led to a decrease in capillary moisture capacity. Thus, the moisture capacity indicator moved from the category “best” (40-50% according to the classification of Kaczynski, 1965) to “satisfactory” (25-30%) or “unsatisfactory” (less than 25%). After washing oil-contaminated soils with surfactant solutions, the values of capillary moisture capacity were restored from the level of “unsatisfactory” to “good” or “best”, although they remained somewhat lower than the level of the parameter of the original (uncontaminated) soil. The results obtained demonstrated an improvement in the studied and so important (in terms of yield) agrophysical parameter of oil-contaminated soil after its treatment with Tween-80. This confirms the prospects of using reagent treatment of oil-contaminated soils using this nonionic surfactant. At the indicated ratio soil: aqueous phase : washing solution, and the contamination level is up to 150 ml/kg (oil) and 300 ml/kg (diesel fuel), the optimal concentration for washing contaminated soil is 5 g/l Tween-80. When reclaiming soils contaminated with oil at a concentration of 300 ml/kg, it is recommended to increase the concentration of surfactants in washing solutions to 10 g/l.
