NAPL source zone characterization and remediation technology performance assessment: recent developments and applications of tracer techniques

Several innovative tracer techniques have been introduced during the past 5 years for enhanced characterization of the “source zones” at sites contaminated with non-aqueous phase liquid (NAPL) wastes. These tracer techniques allow for an in situ estimation of domain-averaged values and spatial patterns for NAPL saturation (Sn), NAPL–water interfacial area (anw), and bio-geochemical reactivity (ks) within the target test zone. The tracer tests can be used to evaluate the spatial patterns in these parameters, both before and after implementing some in situ technique for site cleanup, in order to evaluate the effectiveness of remediation achieved and the possible impacts of the cleanup technology on hydrodynamic and bio-geochemical processes. Here, we review the theoretical and experimental basis for these tracer methods, present selected examples of recent field-scale applications, and examine their reliability.