Background Sediment Assessment in a Great Lakes Estuarine Environment

摘要

A weight-of-evidence approach was used to evaluate anthropogenically-influenced concentrations of polycyclic aromatic hydrocarbons (PAH) in surficial sediment in an urban stream adjacent to a former Manufactured Gas Plant (MGP) Site in Ohio. This evaluation was conducted to help determine whether or not PAH in the stream were attributable to former MGP operations or to other anthropogenic sources in this urban river system. Sediment PAH concentrations were elevated relative to literature-derived background levels and risk-based screening levels in all reaches of the stream. An evaluation of upstream versus near-Site data was complicated due to several mechanisms which could potentially transport PAH from the Site area to reaches of the stream upstream of the Site: (1) groundwater flow pathways at the Site are circuitous and it is possible that some groundwater from the Site actually discharges upstream of the Site; and (2) the seiche effect from nearby Lake Erie is known to routinely cause tidal flow reversals in the stream.Four lines of evidence were evaluated, including: 1. Screening modeling of surface water and groundwater transport,2. Forensic historical information and literature information, 3. Forensic chemical laboratory analyses, and4. Statistical evaluation of upstream versus near-Site sediment. While the individual lines of evidence provide an incomplete assessment relative to the sediment PAH, the combined weight-of-evidence highlights differences between anthropogenic background PAH and MGP-derived PAH in sediment in this urban stream. This paper begins with background information including the history of the Site, and the physical characteristics of the groundwater, surface water, and sediment. Next, the results of sediment chemical analyses, including forensic testing are described. The next section evaluates the potential contribution to high upstream concentrations of PAH due to groundwater and surface water flow. Finally, various statistical tools are used to compare sediment PAH concentrations adjacent to the Site with upstream background conditions.