The Effects of Complex Mixtures of Chemicals in Leachates on the Transport of Pollutants in Groundwater

There has been an increasing interest in the effects of changes in the composition of the pore fluids on the sorptive process.  This growing body of literature shows the the effective solubility of organic compounds is changed by the presence of other organic molecules.  The presence of naturally occurring organic compounds has been shown to increase the solubility of a variety of organic pollutants including PCBs, PAHs, DDT, and others.

The effects on sorption of a particular organic pollutant caused by the presence of other organic chemical compounds are two-fold.  The first effect is a decrease in sorption caused by the formation of aqueous phase complexes.  The second effect increases sorption due to an altering of the sediment surfaces by the organic solvents.  It is usually assumed that this surface alteration is caused by a partial organic coating of the sediment surfaces in some manner.  The relative importance of these two effects on the sorption of a specific pollutant in the presence of an organic-rich model landfill leachate was investigated.

A series of batch sorption experiments between pollutant and sediment in solutions ranging from pure water to 100% leachate were performed to determine the relative importance of these two factors.  Subsequent series of batch experiments were performed at different sediment:water ratios.  The pollutants of interest (phenanthrene and naphthalene), the composition of the leachate, and the sediment were chosen to reflect actual conditions in Wisconsin.  The presence of low levels of leachate does not affect the sorption of phenanthrene or naphthalene to the sediment.

These data provide important information on the adsorptive behavior of a highly hydrophobic compound near the leading edge of a leachate plume.  In addition, these data provide information on the behavior of hydrophobic compounds in river or estuarine systems with low sediment/water ratios.