Vadose zone characterization at a contaminated field site using partitioning interwell tracer technology

The partitioning interwell tracer test (PITT) has been demonstrated to be e ffective in determining volume and spatial distribution of residual nonaque ous phase liquids (NAPLs) in the saturated subsurface. Use of PITT technolo gy in the vadose zone has been limited to this point. Two PITTs were comple ted in the vadose zone of a NAPL contaminated site at Kirtland Air Force Ba se in Albuquerque, NM. The PITTs were completed before and after a thermall y enhanced soil vapor extraction remediation effort, to provide performance assessment. Methane was used as a nonpartitioning tracer. Four perfluoroca rbons (perfluoromethylcyclohexane, perfluoro-1,3-dimethylcycllohexane, perf luoro-1,3,5-trimethylcyclohexane, and perfluorodecalin) were utilized as ai r-NAPL partitioning tracers. Difluoromethane was used as an air-water parti tioning tracer to estimate water saturation. The complex light NAPL (LNAPL) consisted of hydrocarbon fuels ranging from approximately 12-70 carbons in size. Laboratory experimental data a nd thermodynamic modeling were used t o characterize compositional changes in the NAPL due to the remediation eff ort. About 260 kg of NAPL were removed from the subsurface by the remediati on effort. The PITT assessment of the remediation was compared favorably to the results from soil borings taken at the site. The PITT has been shown t o be a useful technology for both NAPL. characterization and remedial perfo rmance assessment in the vadose zone.