Field Evaluation of Interfacial and Partitioning Tracers for Characterization of Effective NAPL‐Water Contact Areas

Publisher Website
Google Scholar
Abstract
The use of surface‐active tracers for measuring the interfacial area between no aqueous phase liquids (NAPLs) and water was evaluated in a hydraulically isolated test cell installed in a surficial aquifer located at Hill Air Force Base (AFB), Utah. Interfacial tracers were developed at the University of Florida for quantifying immiscible fluid‐fluid interfaces (air‐water or NAPL‐water) in porous media. Sodium dodecyl benzene sulfonate (SDBS) was used as the interfacial tracer to measure the effective NAPL‐water interfacial area (aNw), while 2,2‐dimethyl‐3‐pentanol (DMP) was used as the partitioning tracer to estimate the NAPL saturation (SN). The observed retardation of SDBS and DMP when compared to a nonreactive tracer (bromide or methanol) at eight multilevel sampling locations and one extraction well, was used to quantify the aNw and SN values averaged over the interval between the injection wells and each monitoring point. The NAPL morphology index, defined here as HN= aNw/φSN (φ= porosity), varied significantly within the test cell. In locations where the magnitude of HN was large, the NAPL was assumed to be more or less uniformly spread, providing good contact with the mobile fluid. In contrast, regions with low HN values were assumed to have NAPL that was more heterogeneously distributed as isolated patches providing poor contact with the mobile fluid. The index HN, provided by the combined use of interfacial and partitioning tracers, has important implications for NAPL source region remediation employing in situ flushing technologies.