Heterogeneous Organic Matter in a Landfill Aquifer Material and Its Impact on Contaminant Sorption

By Hrissi K. Karapanagioti and David A. Sabatini

ABSTRACT

Phenanthrene was used as a model chemical to study the sorption properties of Canadian River Alluvium aquifer material sampled from the closed Norman Landfill which is a USGS Toxic Substances Research Site in Norman, Oklahoma. Both equilibrium and kinetic sorption processes were evaluated through batch studies. The bulk sample was divided into subsamples with varying properties such as particle size, organic content, equilibration time, etc. in order to determine the effect of these properties on resulting sorption parameters. The data have been interpreted using the Freundlich isotherm model and a numerical solution of Fick's 2nd law in porous media. Organic matter in the subsamples was divided into two main groups based on the microscopic organic matter characterization: a) organic particles (i.e. coal, charcoal, etc.) or mature organic matter and b) organic coatings of quartz grains or young organic matter. Samples containing organic particles presented high Koc values. Samples with organic matter dominated by organic coatings on quartz grains presented low Koc values and contained a high percentage of fast sorption sites. The numerical solution of Fick's 2nd law requires the addition of two terms (fast and slow) in order to properly fit the kinetics of these heterogeneous samples. These results thus demonstrate the need for soil organic matter characterization in order to predict and explain the sorption properties of a soil sample containing heterogeneous organic matter and also the difficulty and complexity of modeling sorption in such samples. Microscopic organic matter characterization proved to be a valuable tool for characterizing the heterogeneous organic matter and explaining the results.