Caption title. "Aug. 1989." "EPA/600-S2-89-039." At head of title: Project summary. Distributed to depository libraries in microfiche. Includes bibliographical references (page 8).

"The full report presents information pertaining to quantitative evaluation of the potential impact of selected parameters on output of vadose zone transport and fate models used to describe the behavior of hazardous chemicals in soil. The Vadose Zone Interactive Processes (VIP) model was selected as the test model for this study. Laboratory and field experiments were conducted to evaluate the effect of sensitive soil and model parameters on the degradation and soil partitioning of hazardous chemicals. Laboratory experiments were conducted to determine the effect of temperature, soil moisture and soil type on the degradation rate. Field scale experiments were conducted to evaluate oxygen dynamics, through depth and time, for petroleum waste applied to soil. Results of laboratory experiments demonstrated that the sensitivity of the degradation rate to changes in temperature and soil moisture was generally greater for low molecular weight compounds and less for high molecular weight compounds. For the two soil types evaluated, soil type was more significant with regard to immobilization. Soil type was not found to have an effect on degradation kinetics for the majority of chemicals evaluated. The effect of oxygen concentration on chemical degradation as predicted by the test model was found to depend upon the magnitude of the oxygen half-saturation constant. Oxygen-limited degradation would be anticipated to occur shortly after the addition of chemicals to soil and during active microbial metabolism of chemicals. Model output results for temperature dependent reactions indicated that depth-concentration profiles would be sensitive to, and directly related to the temperature correction coefficient (0) for each chemical. Model outputs would be very sensitive to soil temperature when values for 8 were 1.04 or greater. Results from laboratory and short- term field studies indicated that sensitive model parameters-of a site- specific nature need to be addressed in modeling the fate and behavior of hazardous chemicals in the unsaturated zone of a soil system."