Effects of oil and grease on the vaporization of organic compounds from contaminated sediments

Contaminated sediments, which contain hazardous compounds such as polynuclear aromatic hydrocarbons (PAHs), are dredged and stored in confined disposal facilities (CDFs). Exposure of the sediment to air results in volatilization of contaminants. Many of the field sediments also contain substantial amounts of oil and grease. An uncontaminated sediment from a local lake (University Lake, Baton Rouge) was spiked with motor oil and PAHs. The air emission flux of three compounds (dibenzofuran, phenanthrene, and pyrene) from the oily sediment was compared to that from the same sediment without oil. The oil content of the sediment was 2.3%, and it had a moisture content of 6.5% to provide 100% pore air relative humidity. Experiments were also conducted with another moisture content of 55% in the sediment. Experiments were performed in dynamic flux chambers in the laboratory. The experimental flux measurements for all three compounds were lowered substantially in the presence of the oil in the sediment. At the end of the experiment, the sediment was cored to obtain the sediment concentration profiles. A mathematical model was constructed based on the hypothesis that the oil served as an additional compartment for the partitioning of the chemicals, and did not contribute an additional layer of resistance to mass transfer resistance from sediments. The comparison of experimental data and the model simulations showed that this hypothesis was true for sediments used in this study, where the oil was immobile.