Contaminated Vadose Zone Characterization Using Partitioning Gas Tracers

This paper describes laboratory research conducted to investigate the performance of partitioning tracers for the detection of nonaqueous-phase liquids (NAPLs) in vadose zones. Once evaluated, the tracers may be used for volume estimation of NAPLs and remediation performance assessment of vadose zones. These laboratory studies used glass chromatography columns packed with: (1) Ottawa sand; and then (2) in a separate experiment, soil extracted from the Chemical Waste Landfill at Sandia National Laboratories. The columns were prepared in a manner that resulted in a three-phase system of air, water, and NAPL in the columns. Conservative and partitioning gas tracers were injected into the columns, and their elution concentrations were analyzed. The method of moments was used to estimate partition coefficients between the air and NAPL phases for each of the tracers. The partition coefficients and retardation factors, also estimated during the study, are used to select appropriate tracers for NAPL detection. This research identified several suitable perfluorocarbon tracers and demonstrated the feasibility of using partitioning tracers as a tool for NAPL detection in the vadose zone.