Comparative assessment of coal tars obtained from 10 former manufactured gas plant sites in the Eastern United States

A comparative analysis was performed on eleven coal tars obtained from former manufactured gas plant sites in the eastern United States. Bulk properties analyzed included percent ash, Karl Fisher water content, viscosity and average molecular weight. Chemical properties included monocyclic- and polycyclic-aromatic hydrocarbon (PAH) concentrations, alkylated aromatic concentrations, and concentrations of aliphatic and aromatic fractions. It was found that there was at least an order-of-magnitude variation in all properties measured between the eleven coal tars. Additionally, two coal tars obtained from the same manufactured gas plant site had very different properties, highlighting that there can be wide variations in coal tar properties from different samples obtained from the same site. Similarities were also observed between the coal tars. The relative chemical distributions were similar for all coal tars, and the coal tars predominantly consisted of PAHs, with naphthalene being the single-most prevalent compound. The C9−22 aromatic fraction, an indicator of all PAHs up to a molecular weight of approximately 276 g mole−1, showed a strong power-law relationship with the coal tar average molecular weight (MW¯ct). And the concentrations of individual PAHs decreased linearly as MW¯ct increased up to ca. 1000 g mole−1, above which they remained low and variable. Implications of these properties and their variation with MW¯ct on groundwater quality are discussed. Ultimately, while these similarities do allow generalities to be made about coal tars, the wide range of coal tar bulk and chemical properties reported here highlights the complex nature of coal tars.