Composition and Properties of Coal Tar DNAPLs at Former Manufactured Gas Plants

Coal tar is a persistent source of groundwater contamination in the subsurface at many former manufactured gas plants (MGPs). Remediation of coal tar remains a significant environmental challenge due to its complex chemical composition, existence as a dense non-aqueous phase liquid (DNAPL), and tendency to alter the wettability of porous media systems. Changes in wettability are believed to occur due to the presence of ashphaltenes, a complex group of high molecular weight surface active compounds. Despite thousands of former MGPs in the US, a thorough investigation into the literature identified less than twenty sites from which coal tar DNAPL was analyzed to obtain data on chemical composition and/or physical properties. Currently, no study exists in the literature which considers multiple samples from a single site. In order to understand the potential universe of coal tar DNAPL and identify current data gaps, we compile all available literature data on coal tar DNAPL including: chemical composition, density, viscosity, and interfacial tension. We also conduct an analysis of multiple coal tar samples from a former MGP and evaluate changes in coal tar composition along the migration path of a DNAPL plume. Finally, we present a method for analyzing the asphaltene content of coal tar along with the results of this analysis.