A Case Study in the Application of Environmental Chemodynamic Principles for the Selection of a Remediation Scheme at a Louisiana Superfund Site

Abstract

This chapter studies the application of chemodynamic principles to select a remediation scheme at a Louisiana Superfund site (Petro Processors, Inc (PPI) sites). The current remediation scheme at the sites, monitored natural attenuation (MNA) is a direct result of this and other research conducted at Louisiana State University. In this chapter, the results from our studies on the adsorption and desorption, the desorption kinetics, the delineation of freely desorbing and desorption resistant fractions, and the bioavailability of the desorption resistant fraction are presented along with the implication of this research for the current remediation scheme.

We observed that only a small fraction of the adsorbed mass would desorb even after a number of successive desorption steps. The investigation on laboratory contaminated soil showed a biphasic behavior, namely an easily desorbed fraction and a desorption resistant fraction. Both field contaminated and aged soils also showed the same behavior. The first stage involved a "loosely bound" fraction and the second stage involved a "tightly bound" fraction. The desorption constants calculated or estimated for the two fractions were employed to obtain the overall expected mass recovery from the contaminated zone at the site. Extremely large time frames were predicted for overall mass removal of Hexachlorobutadiene (HCBD) from the contaminated zone.

An empirical non-linear model was used to describe the bi-phasic nature of desorption with one fraction (labile) being released in relatively short periods of time (typically 24–100 h) and a second fraction (non-labile or irreversible) being resistant to desorption and the parameters estimated. In addition, desorption kinetics of three-month and five-month old contaminated soils showed that progressively less amount of contaminant was available for labile desorption (lower F) compared to freshly contaminated soil.

We observed that for freshly contaminated soil, the compound readily desorbed into the aqueous phase and was available for microbial consumption whereas for soils containing mostly the non-labile material, the contaminant availability was limited by the mass transfer into the aqueous phase. The fraction of contaminant, which is irreversibly bound to soil is typically present in micropores or chemically bound to soil humic matter and thus is not accessible for microbial utilization. These observations are in agreement with those reported for other chemicals in the literature. It is believed that the longer the contaminant age within the soil the lower the fraction of the contaminant that will be bioavailable. The observations have significant implications to the current remedy and the possibility of natural attenuation at the site.