Determining Risk-Based Remedial Goals for Estuarine River and Marsh Sediments at a Former Wood Treating Facility, Gautier, MS

摘要

Background/Objectives. The former Gautier oil site (Site), an approximate 24-acre parcel located within the city limits of Gautier, Mississippi (MS) and bounded by the West Pascagoula River (River) and Bayou Pierre (Bayou), sensitive estuarine wetlands, and predominantly residential properties, was utilized for wood treating (creosote) operations for more than a century, affecting on-site areas and sediments in adjacent waterways. Following cessation of wood-treating operations and removal of above ground structures and waste under an EPA Consent Order in 1985, CSX Transportation, Inc. (CSXT) has worked closely with the MS Department of Environmental Quality (MDEQ) for a number of years to evaluate environmental impacts associated with the Site and adjacent River and Bayou. A risk assessment was performed for the impacted sediments of the River and Bayou and associated estuarine areas. The key issues were residual polycyclic aromatic hydrocarbons (PAHs) in the sediments and their bioavailability/ potential toxicity. The risk assessment was focused on potential direct and indirect impacts of PAHs to the estuarine food web and human exposures via direct sediment contact and ingestion of local seafood, with the overall objective of supporting a riskbased remedy that would be both protective and allow the Site and its environs to be returned to a thriving and healthy part of the surrounding estuary. Approach/Activities. A range of sediment and biological monitoring data were collected to support the risk assessment, to include a sediment quality triad (SQT) assessment conducted to quantify risk from impacted sediments to benthic communities in the aquatic/wetland areas immediately adjacent to the Site. The data indicated that the benthic invertebrate communities in the River and Bayou adjacent to the Site are similar in diversity, abundance and structure to those in reference locations, despite variable and elevated levels of PAHs in surface sediments. Site-specific toxicity was found to be limited-an ecological effects range of 216 to 826 mg/kg total PAH was developed for benthic community impacts. From these data, a conservative remediation goal of 200 mg/kg total PAHs was selected for surface sediments. Results/Lessons Learned. Human health and bioaccumulative food web risks from PAHs were determined to be de minimis. The SQT, in conjunction with a thorough understanding of the ecology and fate/transport processes at the Site, was used to help define potential sediment remediation needs and options. The Remedial Investigation and risk assessment results were used to define the impacted areas to be remediated and to help develop a focused remedy for the sediments at the Site that would reduce exposure