Empirical Evaluation of Contaminant Loading to a Large, Complex, Superfund Site: Portland Harbor Case Study

摘要

Background/Objectives. Understanding the mechanisms, timing, and magnitude of chemical loading to a contaminated sediment site is a key step in a remedial investigation and feasibility study (RI/FS). This step directly informs the development and refinement of the conceptual site model and provides critical data needed to support the development of numerical models, which may be needed to effectively evaluate remedial alternatives in the FS. This case study presents the approach used to evaluate and quantify contaminant loading to the Portland Harbor Superfund Site. The site, a 10-mile industrialized and urbanized reach of the lower Willamette River located just downstream of downtown Portland, Oregon, was listed as a Superfund site in December 2000. The Lower Willamette Group submitted a draft final RI report to the U.S. Environmental Protection Agency in August 2011, followed by a draft FS in March 2012. The work described here was conducted as part of the RI. Approach/Activities. Contaminant loading to Portland Harbor was characterized for a diverse range of media―sediment, surface water, stormwater, groundwater, and air. An extensive sampling plan was implemented to gather data determined to be critical to the RI contaminant loading assessment; this included the sampling of surface water, sediment, transition zone water, and stormwater. To supplement this sampling effort, existing data were gleaned from a range of sources, such as wastewater discharge permits and peer-reviewed literature. Following data collection, the data were analyzed to better understand the magnitude of each source term and the interactions between them. This data analysis focused on providing empirical insight into three site characteristics: (1) ongoing external loading mechanisms, (2) fate and transport processes between media within the site, and (3) the definition of site-relevant upriver chemical concentrations in surface water entering the site and upstream bedded sediments. Results/Lessons Learned.This presentation will provide an overview of the approach used to identify data needs and the data analyses used to inform the later steps of the RI/FS process. This will include an evaluation of the utility of each dataset for this characterization process and the limitations or constraints of the compiled or collected data. For a subset of chemicals, the estimated loading results in the RI will be compared to the modeled results, which were refined in the draft FS.