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Opaque, viscous tars derived from the carbonization of fossile carbon feedstocks, such coal tars and creosote, are long-term sources of groundwater contamination, predominantly with poly-and heterocyclic aromatic hydrocarbons (PAH). The dissolution, aging and migratory behavior of dense, non-aqueous phase liquid (DNAPL) coal tar blobs and pools forming at the aquitard is not sufficiently understood to estimate the risk and adequately design groundwater treatment measures at a contaminated site. In this study, we investigate the composition and dissolution of a migrated, aged creosote DNAPL, and corresponding experimental and groundwater profiles using comprehensive two-dimensional gas chromatography (GCxGC-MS). GC-FID unresolved compounds were attributed to methylated homocyclic species using GCxGC-MS in the Methylanthracene weight range. Equilibrium concentrations were estimated using Raoult's law, assuming non-ideal behavior. Low molecular weight compounds were found to be prevalent even after decades of weathering, with Naphthalene (8% by mass) representing the most abundant identified compound, contrary to the expected preferential depletion of hydrophilic compounds. Morevoer, dimethylnaphthalenes were relatively more abundant in the aqueous boundary layer than in the DNAPL. DNAPL migration over 400 m with the groundwater flow effected lower viscosity and specific gravity of the migrated phase body in a superposition of weathering, transport, and aquifer chromatography effects. Based on a decomposition of analyzed and estimated constituents using the group contribution approach, reference DNAPL values for activity coefficients γ i were used to model aqueous solubilities for selected compounds. Anthracene was close to its theoretical precipitation limit in the bulk DNAPL. While laboratory and modeled DNAPL dissolution behavior agree well, field data imply the presence of specific interfacial in situ processes significantly impacting dissolution processes. Based on aqueous GCxGC-MS profiles over the DNAPL, a hypothetical interfacial in situ film was calculated to be composed primarily of Phenanthrene, with minor contribution by Naphthalene, possibly forming a viscous barrier for the dissolution Scherr et al.Environmental Coal Tar DNAPL Weathering of lower molecular weight PAH. The main advances and gaps in electron donor DNAPL understanding are discussed regarding our conception of weathered, migrating hydrophobic DNAPL bodies in the aquifer of historic contaminated sites for the adequate treatment of contaminated water.

BACKGROUND: Coal tar is a complex mixture of more than 100 compounds, including polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs, phenolic as well as NSO‐heterocyclic compounds (HAC). Many of these are associated with human and environmental risk. Information concerning the environmental fate of coal tar constituents, apart from the 16 PAHs listed as priority substances by the US‐EPA, is scarce. In the current study, aerobic degradation of aromatic tar oil constituents in ten historically contaminated soils was monitored under laboratory conditions using two‐dimensional comprehensive GC2/ MS. RESULTS: Fifty‐four aromatic compounds were detected in one single analysis. Degradation behavior of individual compounds was determined by their hydrophobicity, molecular size, degree of alkylation and isomeric conformation. Eight substances, including six US‐EPA PAHs and two benzofluorene isomers, were identified in nine out of ten soils as principal components in the residual contamination after degradation. CONCLUSION: Using GC2/ MS to reveal the degradation behavior of distinct coal tar constituents and applying PCA to identify contaminants resistant to microbial degradation can be useful for the optimization of bioremediation measures at contaminated sites. Copyright © 2012 Society of Chemical Industry