Partitioning tracer tests for evaluating remediation performance

Partitioning tracer tests (PTTs) are being used in environmental systems for the detection and estimation of nonaqueous phase liquid (NAPL) saturations in contaminated aquifers. A series of such studies was recently conducted at Hill Air Force Base, Utah, in two hydraulically isolated test cells of an aquifer contaminated by light nonaqueous phase liquids (LNAPL). These experiments were performed before and after two remediation efforts, a complexing sugar flush (CSF) and a recirculating in-well aeration (IWA) system. The breakthrough curves obtained from monitoring tracer concentrations in the extraction wells indicated the presence of an immiscible phase, and the LNAPL saturation values determined from the pre- and post-PTTs allowed the estimation of remediation efficiencies for both test cells. These remediation efficiencies, a removal of 43% of the LNAPL for the CSF and an increase of 32% for the IWA system, are consistent with data obtained from cores collected from within the experiment zones. The apparent increase in contamination for the IWA cell is likely due to a significant change in the LNAPL distribution caused by the flow system associated with the IWA technology. Several factors influenced the interpretation of the PTT data. Physical heterogeneities at the site caused significant tailing of the tracer concentrations and required the use of a simple extrapolation technique to account for the concentrations below analytical quantification limits. Degradation affected selected nonreactive and reactive tracers, causing the overestimation and underestimation of LNAPL saturations, respectively. Partitioning tracer tests (PTTs) are being used in environmental systems for the detection and estimation of nonaqueous phase liquid (NAPL) saturations in contaminated aquifers. A series of such studies was recently conducted at Hill Air Force Base, Utah, in two hydraulically isolated test cells of an aquifer contaminated by light nonaqueous phase liquids (LNAPL). These experiments were performed before and after two remediation efforts, a complexing sugar flush (CSF) and a recirculating in-well aeration (IWA) system. The breakthrough curves obtained from monitoring tracer concentrations in the extraction wells indicated the presence of an immiscible phase, and the LNAPL saturation values determined from the pre- and post-PTTs allowed the estimation of remediation efficiencies for both test cells. These remediation efficiencies, a removal of 43% of the LNAPL for the CSF and an increase of 32% for the IWA system, are consistent with data obtained from cores collected from within the experiment zones. The apparent increase in contamination for the IWA cell is likely due to a significant change in the LNAPL distribution caused by the flow system associated with the IWA technology. Several factors influenced the interpretation of the PTT data. Physical heterogeneities at the site caused significant tailing of the tracer concentrations and required the use of a simple extrapolation technique to account for the concentrations below analytical quantification limits. Degradation affected selected nonreactive and reactive tracers, causing the overestimation and underestimation of LNAPL saturations, respectively.