VOC ACCUMULATION AND PORE FILLING IN UNSATURATED POROUS-MEDIA

A series of unsaturated column experiments was conducted to study diff erent grain-scale accumulation mechanisms affecting total uptake of vo latile organic compounds (VOCs) onto a model solid and subsequent remo val of VOCs from the porous media. Experimental variables included VOC (benzene, methylbenzene, 1,4-dimethylbenzene, and 1,3,5-trimethylbenz ene), moisture content (primarily water-unsaturated conditions), and i nfluent VOC concentration. Calculations of the mass distributions of b enzene indicated that it was primarily in the aqueous and air phases w ith a small fraction at the air-water interface. Similar calculations for the other VOCs indicated that greater than 50% of the accumulated mass of these VOCs was located within intraparticle pores and on the s ubstrate surface. Analysis of the sorption data in terms of a pore-fil ling model support the hypothesis that a capillary phase separation (C PS) process occurred within the pores and produced a neat, separate VO C phase. We suggest that CPS will become more critical in materials wi th small mesopores or micropores, and that it is partly responsible fo r the existence of a resistant fraction of VOCs present within water-f illed intraparticle pores.