The partitioning tracer test (PTT) is a characterization tool that can be used to quantify the porespace saturation (SN) and spatial distribution of dense nonaqueous phase liquids (DNAPLs) in the subsurface. Because the method essentially eliminates data interpolation errors by directly measuring a relatively large subsurface volume, it offers significant promise as a remediation metric for DNAPL-zone remediation efforts. This article presents, in detail, the design and results of field PTTs conducted before and after a DNAPL-zone treatment at the Naval Amphibious Base Little Creek, Virginia Beach, Virginia. The results from different tracers yield a relatively large range in SN estimates, indicating notable uncertainty and presenting significant challenges for meaningful interpretation. Several potential interpretation methods are presented, resulting in an estimated DNAPL removal range of 15 to 109 L. While this range is large, it is consistent with the DNAPL removal (∼30 L) determined from analysis of effluent concentration measurements collected during the remediation efforts. At this site, the initial and final SN values are low, and the relatively inconsistent performance of the various tracers indicates that these levels are near the lower practical quantification limit for these PTTs; however, the effective lower quantification limit for these tests is unknown. Generally, an understanding of lower quantification limits is particularly important for interpretation of post-remediation PTTs because SN values are likely to be low (due to remediation efforts) and the SN estimated from the PTT may be used to predict long-term dissolved plume behavior and assess associated environmental risk. Partitioning tracer test quantification limits are test-specific, as they are dependent on a variety of factors including analytical uncertainty, tracer breakthrough characteristics, and tracer data integration techniques. The results of this case study indicate that methods for estimating lower quantification limits for field PTTs require further development.
ASJC Scopus subject areas
- Environmental Engineering
- Waste Management and Disposal