DEPENDENCE OF HYDRAULIC AND PNEUMATIC CHARACTERISTICS OF SOILS ON A DISSOLVED ORGANIC-COMPOUND

The physical properties of the interfaces between solid, liquid, and g aseous phases determine the fate of organic pollutants in soils. Choos ing butanol as a model substance, we investigated the effects of a dis solved organic compound on the relationships between capillary pressur e, phase saturation, and permeabilities of a quartz sand mixture. Stea dy-state column experiments were performed at various degrees of phase saturation using air as the non-wetting phase and aqueous solutions w ith 0%, 2% or 6% (by weight) butanol as the wetting phase. The capilla ry pressure-saturation curves were found to scale according to the sur face tension ratio. While the saturation curves showed considerable hy steresis between wetting and drying with respect to capillary pressure , no hysteresis was found in the hydraulic permeability curves with re spect to saturation and all curves described a unique function of satu ration. Contrary to hydraulic permeability, pneumatic permeability how ever showed significant hysteresis with respect to saturation. The dra inage and imbibition branches of the air permeability functions were n ot found to depend on the butanol concentration. These results indicat e that for a dissolved organic compound the effect of concentration on the hydraulic and pneumatic characteristics of a soil can be predicte d well from a single set of capillary pressure-saturation and permeabi lity-saturation curves if the corresponding surface tensions are known and if changes of contact angles remain small. (C) 1998 Elsevier Scie nce B.V. All rights reserved.