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.