There is a growing body of evidence that soils that contain residual concentrations of contaminants above background or pristine conditions may not pose unacceptable risk to the environment and human health. The initial results of a research program sponsored by the Gas Research Institute support this contention. The GRI research program has reviewed the existing soil literature: (1) to obtain a better understanding of the physical and chemical interactions that bind contaminants within the soil matrix and that govern their rate of release into the environment and to living organisms and (2) to examine and/or develop correlations between soil treatment and the resulting toxicity and mobility of contaminants in the soil matrix. This paper presents a sample of the supporting data which have been found regarding the persistence of contaminants in soil with time; the effects of aging of contaminants on their availability to microorganisms, the extractability of contaminants from the soil and the release of contaminants from the soil into the environment; the effects of the sorption of contaminants on soil on their effective toxicity; and the results of biological treatment on the concentration, toxicity, and mobility of PAHs in soil. The implications of these findings on the determination of environmentally acceptable endpoints in contaminated soils and the management of contaminated sites are also discussed.

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