Application of the gas-phase partitioning tracer test method to measure the saturation of a complex NAPL 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.