Abstract

 Laboratory studies were conducted to evaluate the equilibrium partitioning of coal tar constituents between water and sediment collected in a river adjacent to a former manufactured gas plant (MGP) in Northern Indiana. These measurements were made in anticipation of additional studies designed to measure the advective and diffusive fluxes of coal tar constituents through the contaminated sediment. Cores (4-inch ´ 8-ft) collected at five locations, were sectioned at their midpoint, and homogenized to provide 10 composite samples. Volatile (105o C), ignitable (500o C) and organic carbon contents were measured on each sample, as well as total sediment and equilibrium aqueous phase concentrations of 16 major PAH and monocyclic aromatic hydrocarbon contaminants. GC-FID analysis and inspection of cores show that nonaqueous phase liquid (NAPL) is present in each of the 10 samples. Contaminant concentrations generally followed the order (from highest to lowest concentration) naphthalene > 2-methylnaphthalene > phenanthrene > acenaphthene > pyrene " fluorene " anthracene > fluoranthene > chrysene " benzo (a) anthracene > acenaphthalene > ethylbenzene > o-xylene " m-xylene + p-xylene > 1,3,5-trimethylbenzene. The composition of the NAPL at the different locations is approximately the same despite variation in the absolute amount of NAPL at the different sampling locations. For example, in all ten samples, naphthalene is approximately 12% of the total mass of the tar, whereas chrysene is approximately 1%, with total naphthalene concentrations ranged from 1.90 mg / g to 16.7 gm / g sediment dry weight. Sediment-water partition coefficients of all 16 compounds in each sample, normalized to NAPL content (Kp in dimensionless units), compared very favorably to theoretical liquid-liquid partition coefficients that assume each component's activity within the NAPL phase is ideal. Hence, the theoretical equilibrium pore-water contaminant concentrations are easily predicted from tar composition.