Thermal Desorption Temperature Affects Water Retention and Hydraulic Conductivity of Three Contrasting Soils

Thermal desorption is an effective approach to removing petroleum hydrocarbons from soil. However, the resultant environmental function and revegetation potential of the soil can be reduced by high temperatures. This study evaluated the effect of nine temperatures of heating (60–800°C) on water retention and hydraulic conductivity in three soils of contrasting mineral and physical properties. Fredlund-Xing water release curves were developed using the HYPROP system. Features of the release curves were compared for differences: the water content (%Vol) at which air first enters the macropore volume (AEV), the slope of the rapid desorption portion of the curve, field capacity, and the residual water content. A Hearne sandy loam showed an increase in the %Vol at saturation (0.354 to 0.557 cm3 H2O cm−3 soil), but a decrease in plant available water with increasing temperature. A Rader sand showed a decrease in field capacity and plant available water. A Weswood clay showed no change in field capacity, but an increase in plant available water 10.87 to 18.39 cm3 H2O cm−3 soil through 700°C. Saturated hydraulic conductivity (Ksat) increased for both the Hearne and the Weswood soils with increasing temperature. However, the Rader soil Ksat saw an increase from 0.002 to 0.007 cm s−1 to 450°C but declined to <0.0005 cm s−1 between 500°C and 800°C. This study shows the release curve comparison approach can be effective to quantify changes or differences in soil water relationships by treatment or soil property. Additional insight is provided by electron microscope imaging.