The discussions in this chapter deal with interparticle actions in the presence of an aqueous phase. The importance of the aqueous phase presence is that this liquid phase serves as the carrier or medium for transport of contaminants that interact with the soil solids (particles). The term “attenuation” used in the context of contaminant interaction in soils is not always properly understood. The intent of this chapter is to inform the reader that there are many more mechanisms involved in contaminant attenuation than microbial intervention. Knowledge of the basic interactions between soil solids and contaminants or dissolved solutes in the porewater is necessary if we are going to develop a better appreciation of the factors that contribute directly to the assimilative capacity of soils. The nature of the reactive surfaces in the soil-water system, and how these surfaces are obtained will give us insight into how the soil conditions in the field will impact directly on the transport and fate of the contaminants under consideration.

For effective attenuation of contaminants in a candidate site, it is necessary for the soils in the site to possess attributes (characteristics and properties) that when interacting with the contaminant stream will achieve toxicity and/or contaminant concentration reduction. This requires one to develop a more detailed understanding of the interactions or processes that occur in the soil depend not only on the properties and characteristics of the contaminants, but also on the properties and characteristics of the soils. All too frequently, assessments and evaluations of natural attenuation of contaminants overlook the fact that the abiotic and biotic reactions between contaminants and soils need the same detail in determination of the various attributes of the soil that participate in those reactions.