| Leaks, spills, subsurface disposal of petroleum products and industrial solvents have contaminated groundwater systems with hydrophobic organic compounds including polycyclic aromatic hydrocarbons (PAHs). A variety of soils, chemical, and hydrologic factors control the mobility of dissolved natural organic matter (DNOM), which may enhance or retard the transport of associated contaminants such as PAHs. Developments of technologies to remediate contaminated sites are dependent on understanding the mechanisms of soil-contaminant-water interactions.; The transport of PAHs were studied in the presence and absence of natural organic matter (NOM) in both batch and column experiments. In batch experiments, both binary systems (including the interactions between PAHs/NOM, PAHs/minerals, and DNOM/minerals) and ternary systems (including the interactions among PAH/NOM/minerals) were studied. A one-dimensional advective-dispersive transport model (CXTFIT) was used to simulate the breakthrough curves (BTCs), and confirm the sorption mechanism and the kinetic phenomenon.; Results from binary systems showed that ligand exchange was the dominant mechanism for DNOM sorption onto mineral surfaces. This was supported by the following observations: non-linear sorption isotherms, fast sorption rates with slow desorption rates and extended tailings, solution pH increased during DNOM sorption, phosphate displaced sorbed DNOM and SOM. It was also suggested that low solubility with water was the driving force and functional group density was the determining factor for DNOM sorption. Hydrophobic effect was the dominant factor for PAH sorption, and the kinetic effect needs to be considered.; Results from ternary systems showed that DNOM facilitated PAH transport and enhanced PAH desorption. Humic fractions have higher affinities for PAHs, but they also retarded PAH transport by sorption onto minerals. PAH diffusion through a SOM phase was likely the rate-limiting step in this process. Phosphate can potentially be used as a remediation "solvent" to clean soils or sediments contaminated by HOC that is partitioned in SOM.; Results from CXTFIT model simulations showed that chemical nonequilibrium occurred when DNOM sorbs onto mineral surfaces, and physical nonequilibrium occurred when PAHs partition into SOM. The kinetic two-site nonequilibrium CDE predicted DNOM sorption well. The kinetic two-region nonequilibrium CDE fitted the BTCs of PAHs well for both sorption and desorption. |
