Characterization of spatial NAPL distribution, mass transfer and the effect of cosolvent and surfactant residuals on estimating NAPL saturation using tracer techniques

The non-aqueous phase liquid (NAPL) specific interfacial area and morphology as a function of pore size and NAPL dissolution were studied using the interfacial and partitioning tracer techniques. The NAPL-water interfacial areas increased in a log-linear fashion with decreasing grain sizes used as porous media but did not show a clear trend with residual NAPL saturation formed in the various grain sizes. At a given grain sized, however, the interfacial areas showed a proportional linear relation to a decrease in NAPL saturation by dissolution. The NAPL morphology indices, which represent the spatial NAPL distribution, increased exponentially with decreasing grain size.; Mass transfer across interfaces between NAPL and the aqueous phase was investigated. The investigations consisted of the influence of specific interfacial area, NAPL saturation, grain size, and aqueous phase velocity on mass transfer. Bulk mass transfer rate coefficients increased with increasing the specific interfacial area as well as NAPL saturation and pore velocity, and with decreasing grain sizes. Whereas, intrinsic mass transfer coefficients were nearly independent of specific interfacial area and NAPL saturation, but dependent on pore velocity. Reduction of NAPL saturation by dissolution caused a linear decrease in the bulk mass transfer rate coefficients. Phenomenological correlation models developed using dimensionless Sherwood number produced good prediction for bulk and intrinsic mass transfer coefficients.; A series of batch and column tests was conducted to elucidate the influence of residual cosolvents and surfactants on partitioning and transport of alcohol tracers through soil columns containing residual tetrachloroethylene (PCE). Batch equilibrium tests showed that as the volume fraction of cosolvents (≤10%, vol.) increased, partitioning coefficients for alcohol tracers linearly decreased for ethanol, linearly increased for tert-butanol, and did not exhibit an evident relationship for isopropanol. The column tests using ethanol as a residual cosolvent exhibited earlier partitioning tracer breakthrough which caused an under-estimate of NAPL saturation. The under-estimates of NAPL saturation were 1 to 10% lower than the actual saturation. Comparison between low (0.5%) and high (15%) saturation columns revealed that the effect of residual cosolvent was different depending on the amount of NAPL in the column.; The influence of residual surfactants in aqueous and adsorbed phases on tracer transport behavior was evaluated by estimating PCE saturation using partitioning tracers. The batch equilibrium tests using residual surfactants ranging from 0.05 to 0.5% by weight showed that as the concentrations of the surfactants increased, the partitioning coefficients linearly decreased for Diphenyl oxide disulfonates (DowFax 8390), increased for Polyoxyethylene (10) oleyl ether (Brij 97), and decreased slightly or exhibit no observable trend for Sodium dihexyl sulfosuccinate (AMA 80). Results from column tests using clean sand media with residual DowFax 8390 and PCE were consistent with those of batch tests. In the presence of DowFax 8390 (less than 0.5% by weight), the PCE saturations were underestimated by up to 20%. Adsorbed surfactants on a loamy sand soil with strongly positive charged oxides without PCE showed false indications of PCE saturation. Using no surfactant (background soil) gave a false PCE saturation of 0.0004 while AMA 80, Brij 97, and DowFax 8390 gave false PCE saturations of 0.0024, 0.043, and 0.229, respectively.