EVALUATION OF IN-SITU COLUMNS FOR CHARACTERIZING ORGANIC CONTAMINANT SORPTION DURING TRANSPORT

In situ columns were evaluated for their reliability for characterizing organic contaminant transport and sorption in the saturated zone. A solute transport model which considers one-dimensional flow, point-source input, two-dimensional mass transport, and nonequilibrium sorption during transport within the cylindrical in situ column was developed and applied to simulate experimental data at two field sites. A nonreactive tracer was used to characterize hydrodynamic properties within the in situ column. Independent measurements of equilibrium and nonequilibrium sorption parameters were obtained from laboratory miscible displacement experiments on the same porous media as for the in situ studies. Values of the equilibrium sorption constant, K(p), sorption rate coefficient, k2, and fraction of sorption that attained rapid equilibrium, F, were determined for three sorptive solutes (benzene, toluene, p-xylene; BTX) in laboratory column studies and fixed in simulations of the in situ column data. The simulations were in good agreement with the experimentally measured in situ breakthrough curves. The ability to characterize BTX transport in soils, sediments, and aquifer materials low in organic carbon content is important for management and remediation of gasoline-contaminated-groundwater. The experimental and theoretical technique presented here was applied successfully for characterizing sorptive solute transport at three field sites. With proper model validation and appropriate tracer studies, the in situ technique could be used to obtain site-specific estimates of equilibrium and nonequilibrium sorption parameters (K(p), k2, and F).