Thermally Driven Water and Octane Redistribution in Unsaturated, Closed Soil Cells

Abstract

AbstractTemperature‐gradient influences on non‐aqueous‐phase liquid (NAPL) distribution in soil have received little detailed study, although there have been proposals to employ such gradients in remediation of NAPL contamination. The goal of this study was to characterize the time dependence and ultimate steady‐state distributions of water and octane after a constant temperature difference had been imposed across a volume of soil. Cells 5 cm long were packed with soil of initially uniform water and octane content. Temperatures at opposite ends of the cells were established and maintained at 40 and 6°C. Cells were destructively sampled at seven times from 1.5 to 100 h. Octane moved toward the cool end of the soil within 1.5 h. Water redistributed more slowly, but continued to do so for > 12.5 h. Water concentrating at the cool end of the cells resulted in reversal of the initial movement of octane at times > 1.5 h. The final steady‐state distribution of water in the cells had > 95% of the total water within the 3 cm nearest the cool end. In contrast, octane showed a peak at the location where water content dropped sharply. The interval 3 to 4 cm from the cool end contained 28% of the total octane in the cells. This study indicates that using thermal gradients effectively for concentrating NAPL will be a complex undertaking.