Distinguishing PAH Background and MGP Residues in Sediments of a Freshwater Creek

Abstract

Polycyclic aromatic hydrocarbons (PAHs) in the environment have origins in various natural and anthropogenic sources. Pyrogenic tars (e.g., coal tar) are rich in PAHs, which are therefore typical constituents of concern at former manufactured gas plant (MGP) sites. Delineating the extent of PAHs in sediments is a common component of many former MGP remedial investigations. Because of the compositional similarity of weathered/degraded coal tar residues to combustion-related PAHs that comprise typical urban background, it can be difficult to determine the local PAH background contribution in sediments near MGP sites. This article presents an investigation of Mill Race Creek, a freshwater creek that flows adjacent to the Oneonta, New York former MGP. From the delineation sampling, elevated PAH concentrations were measured in “background” areas upstream of any suspected MGP releases. PAH fingerprinting revealed three primary PAH sources in creek sediments: low molecular weight (LMW), 2- and 3-ring PAHs from background petroleum sources; high molecular weight (HMW), 4- to 6-ring PAHs from site-related sources; and HMW PAHs from background sources. The results of this investigation demonstrated that site-related PAH residues were primarily localized in the subsurface of a few sediment deposits adjacent to the former MGP. Sediments containing site-related PAHs were generally buried underneath a surficial (6 in) layer of sediments with total priority pollutant PAH concentrations (55.0 ± 48.8 mg/kg) that were almost entirely attributable to local background sources. In the context of a remedial investigation, contributions from uncontrolled background PAHs may limit the practicable feasibility of some remedial options.