Application of Thermo-Time Domain Reflectometry Techniques to Detect Mineral Oil-Contaminated Soil.

After a pollutant reached the groundwater, we often notice the pollution of soil and/or the groundwater for the first time. When a pollutant reaches the groundwater, the pollutant spreads along with groundwater flow. Because the pollutant spreads in wide areas, its removal becomes very difficult and time consuming. It is important to detect a trace of the pollutant in unsaturated soil before it reaches the groundwater. For the early detection of pollution, simple monitoring techniques have been sought. Therefore, the purpose of our research was to evaluate the applicability of a thermo-time domain reflectometry (thermo-TDR) technique to measure mineral-oil dynamics in soil. Soil used was a volcanic ash soil known as Kanto-loam. The soil was mixed with predetermined ratios of kerosene and water for various contents of those liquids. We used a three-wire thermo-TDR probe (0.040m long, 0.0075m spacing, Nichrome heater wire encased in the central rod and type T thermocouples in the rods of both ends) for measurements. Volumetric heat capacity was measured with a dual-probe heat-pulse technique, and was dielectric constant with TDR. The values of volumetric heat capacity and dielectric constant for mineral oil are dissimilar to those for other constituents. It is a promising sign for detecting oil in soil. We carried out this experiment to investigate the relationship among oil concentration, volumetric heat capacity, and dielectric constant. A thermo-TDR probe was horizontally installed in the wall of a soil column (30cm height, and 10cm in diameter). Kerosene was applied at the soil surface of the column. Changes in volumetric heat capacity and dielectric constant were detected during kerosene was infiltrating in soil.