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Sediment Assessment and Remediation Report

Assessment of Contaminated Sediments in Slip C, Duluth Harbor, Minnesota

Submitted to
Scott Cieniawski, Project Officer
Great Lakes National Program Office
U.S. Environmental Protection Agency
77 West Jackson Boulevard
Chicago, Illinois 60604-3590


Judy L. Crane
Environmental Outcomes Division
Minnesota Pollution Control Agency
520 Lafayette Road
St. Paul, Minnesota 55155-4194



Contaminated sediments contribute to many impaired uses at Great Lakes Areas of Concern (AOCs) including: fish advisories, habitat impairments, and restrictions on dredging. All of the current 42 AOCs are impacted by sediment contamination based on the application of sediment quality guidelines (Zarull et al. in press). In many cases, contaminated sediments represent a nonpoint source of pollutants to these AOCs, and may pose an unacceptable risk to aquatic organisms, aquatic-dependent wildlife, and human health. Successful remediation of contaminated sediments is essential for restoring impaired uses and contributing to the de-listing of AOCs.

The EPA’s Assessment and Remediation of Contaminated Sediments (ARCS) Program provided a set of sediment assessment, risk assessment, modeling, and remediation tools for contaminated sediment investigations (USEPA 1993, 1994 a,b). The sediment assessment techniques recommended by the ARCS program promoted using a weight-of-evidence approach to conduct sediment chemistry analyses, sediment toxicity tests, and benthological community surveys on synoptic, surficially-collected sediment samples (USEPA 1994a). In particular, the sediment quality triad approach (Long and Chapman 1985; Long 1989; Chapman 1992) provided both a qualitative and quantitative means by which these data could be integrated together. The ARCS program also provided guidance on field sampling and chemical analysis procedures for deeper core segments (USEPA 1994a). The work products and recommendations of the ARCS program have been implemented in the St. Louis River AOC, located in northeastern Minnesota. The Minnesota Pollution Control Agency (MPCA), and its collaborators, as well as the Wisconsin Department of Natural Resources (WDNR), U.S Army Corps of Engineers, and some potentially responsible parties have conducted a number of sediment assessment investigations in this transboundary waterway between Minnesota and Wisconsin (Fig. 1). For the most part, these studies have followed an ecosystem-based management approach, involving citizens and other stakeholders in the decision-making process (MacDonald and Crane in review). These studies have shown that the AOC includes relatively clean areas, in addition to several areas contaminated with a variety of toxic and bioaccumulative substances. Mercury and polycyclic aromatic hydrocarbons (PAHs) are widespread contaminants of concern in depositional areas of the lower St. Louis River estuary, whereas metals, polychlorinated biphenyls (PCBs), dioxins and furans, organochlorine pesticides, tributyltin, and diesel range organics (DROs) tend to be more localized contaminants of concern (MPCA and WDNR 1992, 1995; Redman and Janisch 1995; Schubauer-Berigan and Crane 1996, 1997; Normandeau Associates 1996; TMA 1996; Crane et al. 1997; IT Corporation 1997; Breneman et al. in review). Several hot spot areas of elevated contamination occur in the Duluth/Superior Harbor, including two Superfund sites (i.e., the Interlake/Duluth Tar and USX sites), Hog Island Inlet/Newton Creek, several boat slips (e.g., Minnesota Slip, Slip C, Howard’s Bay), in the vicinity of historical and current wastewater treatment plants, and other areas with historical sources of contamination (e.g., Grassy Point) (Fig. 1) (Schubauer-Berigan and Crane 1997; Crane et al. 1997). Additional background information on the extent of sediment contamination in the St. Louis River AOC is given in the Stage I Remedial Action Plan (RAP) (MPCA and WDNR 1992, 1995) and in MacDonald and Crane (in review). During 1996, the MPCA solicited input from the Sediment Contamination Work Group of the St. Louis River Citizen’s Action Committee (CAC) to assist them in selecting an appropriate site for a sediment remediation scoping project. The group selected Slip C, in the Duluth Harbor, as the best candidate site because: the contamination was well-contained within the slip; several surficial contaminants exceeded benchmark sediment quality guidelines (Persaud et al. 1993); the sediments contained bioaccumulative contaminants (e.g., PCBs, mercury) in the surficial and deeper sediment layers; significant acute sediment toxicity had been observed at the site in the past; and the benthological community was composed of organisms associated with degraded environments (Schubauer-Berigan and Crane 1997; Crane et al. 1997). In addition, the site was manageable for the budget available for this study. The group felt this site had a high potential for being effectively remediated in the future.

The purpose of this sediment remediation scoping project was to further delineate the extent and depth of contamination in the inner half of Slip C. The primary contaminants of concern were eighteen PAH compounds, congener-specific PCBs, mercury, and lead. Total organic carbon (TOC) and particle size classes were also measured. If possible, the volume of contaminated sediments was to be estimated, and preliminary remediation options assessed. In addition, a sediment management plan was to be developed for this site.


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