Abstract
Hydrophobic organic contaminants released from non-aqueous phase liquids (NAPL) impose a serious risk on groundwater quality. NAPL can exist as coherent “pools” or residual phase (“blobs” or “ganglia”) within the aquifer. Depending on the NAPL volume the time scale of contaminant emission may be centuries or longer. The concentration in groundwater depends on the NAPL volume and the interfacial area between NAPL and water. The knowledge of these parameters is essential for site characterization, risk assessment and planning of in-situ aquifer remediation techniques. This paper describes the characterization for NAPLs using partitioning (volume) and interfacial tracers. Laboratory studies (undisturbed soil cores, batch experiments) were conducted using coal tar contaminated material from a former manufactured gas plant site. Different alcohols (substituted pentanols) have been tested as partitioning tracers. An anionic surfactant (ethoxylated alkyl sulfate) was used as interfacial tracer. The alcohols have low but significant octanol/water partition coefficients Kow between 24 and 240 resulting in NAPL/water partition coefficients between 1 and 22. The surfactant accumulates significantly at the NAPL/water interface. While these reactive tracers were not retarded by the natural aquifer material, they were retarded in the presence of NAPL with respect to the transport of a conservative tracer. A surfactant flushing was applied to the contaminated column in order to enhance solubilization of tar oil constituents. The NAPL saturation calculated from the retardation factor and the equilibrium NAPL/water partition coefficients decreased from 30% to 17% in the pre- and post-surfactant flushing system, respectively.
Published Version
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