Quantification of the saturation degree of nonaqueous phase liquid in the vadose zone using hydrocarbon partitioning tracers

摘要

Partitioning tracer tests, as an alternative to the core sampling method, were conducted to quantify the degree of saturation of water and nonaqueous phase liquids (NAPL) in the vadose zone. Hydrocarbon gases, which have less effect on global warming than conventional tracers, were used as partitioning tracers. Column tests using CH_4, C_3H_5, and C_4H_(10) as non-partitioning and partitioning tracers were performed to determine the retardation factor and partition coefficient of the tracer into water and NAPL. The retardation factors of these tracers were estimated to be in the range of 1.0-7.0 based on breakthrough curves of the tracers. The partition coefficient of C_3H_5 to water and diesel phase was calculated to be 0.57 and 8.45, respectively. For a heavier tracer, C_4H_(10), the partition coefficient to the water and diesel phases was 1.2 and 40.5, respectively. The average value of water and diesel saturation estimated from column tests agreed well with known values in unsaturated soil. A residence time longer than 7.5 h within soil pores was found to provide local equilibrium partitioning of the tracer to the diesel phase. The concentration of tracer had no effect on the partitioning process.