Application of the Gas-Phase Partitioning Tracer Test Method to Measure the Saturation of a ComplexNAPL in soil

A series of laboratory experiments was conducted to test the effectiveness of the gas-phase partitioning tracer test (GPTT) method for measuring the saturation of a complex, multiple-component nonaqueous phase liquid (NAPL) in soil collected from a Superfund site. The suite of partitioning tracers included sulfur hexafluoride (SF6), perfluoro-dimethylcyclohexane (C8F16), and perfluoro-trimethylcyclohexane (C9F18). Batch experiments were conducted to characterize sorption, air-water partitioning, and air-NAPL partitioning behavior of the suite of tracers. Batch testing confirmed the use of SF6 as a non-reactive tracer and the two perfluorocarbons as effective NAPL-partitioning tracers. The results of baseline column experiments confirmed the results of the batch testing, showing near ideal transport of the partitioning tracers in columns packed with wet uncontaminated soil. A tracer test conducted for a column artificially contaminated with site NAPL produced NAPL saturations of 0.15 and 0.12 for C8F16 and C9F18, respectively. These values compare well to the measured NAPL saturation of 0.145. Tracer tests conducted for columns packed with field-contaminated soil produced NAPL saturations ranging from 0.002 to 0.012, which are in the lower range of measured values (0.001 to 0.046). These results indicate that the gas-phase partitioning tracer method provided reasonable measurements of NAPL saturation for a complex, multiple-component NAPL collected from a field site.