Date of Award

1988

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

Rights

info:eu-repo/semantics/openAccess

Abstract

Studies were undertaken to evaluate the behaviour of perchloroethylene, PCE, in unsaturated soil to provide remedial actions for minimizing the possible soil and groundwater contamination after a spill. Processes that were investigated included volatilization from water and soil, determination of degradation potential, evaluation of adsorption - desorption isotherms for various granular media and the simulation of a PCE spill on a soil column. Results were then used to calibrate a contaminant transport model.

Sandy loam soil, organic top soil, peat moss and granular activated carbon, GAC, were investigated for adsorption - desorption properties. It was determined that the adsorption - desorption processes were well represented by the Freundlich Isotherm. The governing factor in adsorption was the organic carbon content. The higher the organic carbon content, OC, the greater was the adsorption and retention of PCE by the medium. In dividing the Kf coefficient with the oc content, a Koc of 330 L/mg was determined which indicates that PCE has medium mobility in soil. Results on residual saturation values for the four media indicated that peat moss could retain the highest quantity of pure PCE, 7.8 kg/kg, making it ideal for application at a spill site to retain the chemical. Desorption did not increase with a decrease in pH of the aqueous solution.

The experiments on volatilization of PCE f~om water in~icated that this rate was rapid and that it was influenced by the area to volume ratio, A/V. The volatilization rate increased with an increase in A/V. The overall liquid film coefficient for the water-air interface was 0.009 m/h. Volatilization from soil was also a function of area to volume ratio. However, it was observed that the QC content of soil influenced the volatilization rate. The volatilization rate decreased with an increase in QC content. The mass flux experiment indicated that submerged PCE followed a first , order mass· transfer rate, with a flux rate of 0.028 kg/m2/d. At the chemical-water interface the overall liquid film coefficient was found to be 0.006 m/h.

Equations for the prediction of breakthrough times in soil were determined. The soil properties greatly influenced the penetration distance and the front velocity. Under a 76 mm/d rainfall intensity, the PCE moved at 0.084 m/d and 0.026 m/d in the sandy loam soil and organic top soil respectively. The calibrated contaminant transport model for unsaturated soil prediets the breakthrough time and PCE concentrations. Furthermore, the model and column studies showed that the immiscible phase movement had a significant impact on the PCE concentrations observed in the soil profile.

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