3
Transport Parameters for
Firing Range Residues
Introduction
Transport parameters quantitatively describe the potential movement of
contaminants from the soil surface into the soil matrix and, subsequently, into
surface or ground water. These parameters are required for adequately simulating
transport by numerical modeling of vadose zone and groundwater systems.
Transport parameters are also useful in environmental risk assessments to define
exposure potential for contaminant receptors.
The dissolution rate of explosives residues from free product on the soil
surface or from cracked or partially fragmented munitions is one of the main
processes affecting fate and transport of explosives on firing ranges.
Concentration gradients observed in the soil profile are consistent with kinetic
limitations on solubilization and with different rates of dissolution for TNT, RDX
and HMX (Jenkins et al. 1997). However, the data are limited. Thiboutot et al.
(1998) have also shown that the rates of dissolution of TNT and HMX from the
formulation octol differ substantially. Accurate dissolution kinetics for
explosives and for explosives formulations are key to describing the fate and
transport of explosives residues from firing ranges into groundwater.
Once the residues are in solution, the main factor affecting fate and transport
of explosives residues is advection; contributing factors are adsorption,
transformation, and irreversible soil binding (Brannon and Myers 1997). The fate
and transport process descriptors required for estimating the movement of
explosives residues through soil and into groundwater are the adsorption
coefficient and the transformation rate coefficient. The adsorption coefficient is a
mathematical expression that describes the distribution of a chemical compound
between soil and water at equilibrium. The transformation rate coefficient is a
kinetic parameter that describes the removal of a contaminant from solution
when equilibrium is unattainable due to confounding processes. When
transformation and/or irreversible sorption are pronounced, equilibrium is not
attainable and the transformation rate coefficient is appropriate for describing
fate and transport. One example of this is the partitioning of TNT under certain
conditions that promote reduction of nitro to amino groups with subsequent
changes in partitioning and with chemical reactions between the reduction
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Chapter 3 Transport Parameters for Firing Range Residues
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