In the late 1800s and early 1900s, collaborative funding by some of the nation’s leading tycoons led to development of Duluth, Minnesota and the surrounding area. This included Andrew Carnegie, Jay Cooke, Andrew Mellon, J. P. Morgan and John D. Rockefeller, to name a few. This tremendous period of growth and expansion included major industrial developments, including grain, lumber, iron mining, manufacturing, rail, shipping and shipbuilding, and associated development of the frontier. Although critical to the development of a vital community, these activities took a toll through unchecked alteration of natural habitat and contamination of St. Louis River estuary sediments. These adverse legacy impacts, which occurred well before the establishment of our current environmental regulatory framework, became well recognized in 1985 when the International Joint Commission’s Great Lakes Water Quality Board identified the St. Louis River as an Area of Concern requiring the development and implementation of a remedial action plan to restore all impaired beneficial uses. This commitment to Remedial Action Plans was then codified in the 1987 Protocol to the U.S.-Canada Great Lakes Water Quality Agreement. The initial Stage 1 Remedial Action Plans for the St Louis River Area of Concern was completed in 1992 with the initial Stage 2 Remedial Action Plan completed in 1995, followed by periodic updates through 2012. However, these updates did not have budgets and action timelines necessary to secure the financial commitments to implement identified actions. Establishment of the Great Lakes Restoration Initiative in 2010 led to the 2013 Remedial Action Plan update (i.e. Stage 2 Remedial Action Plan) that included a business plan that identified specific actions, timelines, and budget estimates. Minnesota began implementing recommendations utilizing collaborative funding through a partnership approach. Ninety-nine percent of the actions identified in the Remedial Action Plan have been completed or are currently underway. Funding needs and sources have been clearly identified and the project is on track to complete major actions by 2020 and remove all beneficial use impairments and delist as an Area of Concern, dependent upon confirmation of use restoration, by 2025.

Introduction

The St. Louis River is one of 42 Great Lakes Area of Concern (AOC) identified in 1985 by the Great Lakes Water Quality Board of the International Joint Commission where a comprehensive remedial action plan (RAP) was needed to restore all beneficial use impairments (BUIs). These commitments were then codified in the 1987 Protocol to the Great Lakes Water Quality Agreement (Canada and U.S., 1987). The RAP process, at that time, was innovative because it incorporated a comprehensive and systematic ecosystem approach that included substantial stakeholder participation (Hartig and Thomas, 1988; Hartig and Vallentyne, 1989).

Historical actions such as improper municipal and industrial waste disposal and unchecked land-use practices, including dredging and filling of aquatic habitat and damaging industrial development practices, contributed to the complex set of issues facing the St. Louis River AOC at the time it was listed. The Stage I RAP (MPCA and WDNR, 1992) determined that nine of 14 possible BUIs existed in the St. Louis River AOC, including: fish consumption advisories; degraded fish and wildlife populations; fish tumors and other deformities; degradation of benthos; restrictions on dredging activities; excessive loadings of sediment and nutrients; beach closings and body contact restrictions; degradation of aesthetics; and loss of fish and wildlife habitat. In addition to these BUIs, the St. Louis River AOC is spatially large and geographically complex, spanning the Minnesota and Wisconsin state line and including the Fond du Lac Reservation (Nagaajiwanaang) tribal interests. The AOC boundary includes the lower 63 km of the St. Louis River, from upstream of Cloquet, Minnesota, to its mouth at the Duluth/Superior Harbor and Lake Superior, and the Nemadji River watershed (Figure 1).

A Stage II RAP, completed in 1995, identified the remedial and regulatory measures required for restoration of the area (MPCA and WDNR, 1995). Most of the actions, however, occur in the St. Louis River below Fond du Lac Dam, Crawford Creek, and the Nemadji River watershed, as they represent those portions of the AOC most impacted by historical actions. In the spirit of adaptive management where assessments are made, priorities set, and actions taken in an iterative fashion for continuous improvement, RAP progress reports/updates were prepared in 2001, 2011 and 2012, with a major revision and focused recalibration occurring in 2013 (LimnoTech Inc., 2013a). Annual progress reports have been prepared for work conducted in federal fiscal years 2014, 2015, 2016 and 2017. The Minnesota Pollution Control Agency (MPCA) and the Wisconsin Department of Natural Resources (WDNR) are the regulatory agencies designated by the U.S. Environmental Protection Agency (USEPA) to address the St. Louis River AOC. The purpose of this paper is to share how creative partnerships and collaborative funding have been used in Minnesota to address long-standing issues like contaminated sediment and loss of habitat as part of developing a roadmap to restoring impaired beneficial uses necessary to delist the AOC.

Methods

To demonstrate how collaborative funding was used to achieve implementation of necessary actions to restore impaired beneficial uses, a comprehensive review and evaluation of all RAP activities was performed since RAP onset in 1985. All St. Louis River RAP reports (MPCA and WDNR, 1992, 1995; LimnoTech, Inc., 2013a) and peer-reviewed literature were used to undertake this management review and evaluation. More detailed information on methods and quality assurance procedures is presented in Crane et al. (2002), LimnoTech, Inc. (2016a,b, 2013b), MPCA (2015a,b,c,d), RTI Laboratories (2015), Somat Engineering (2012a,b), U.S. Army Corps of Engineers-Detroit District (2017, 2016, 2015), and Weston Solutions, Inc. (2012a,b). Because this is a review article, summary data and information are used to describe management efforts and draw overall conclusions.

Legacy development period: Development for natural resource use by early tycoons

Duluth, Minnesota began developing shortly after the 1854 Treaty of LaPointe opened land north of Lake Superior for settlement by Americans of European descent (Table 1). Between 1856 and 1859, pioneers established eleven townships, which with a few additional townships, would eventually come together between 1888 and 1896 to form the City of Duluth. In 1855, Henry Wheeler walked from St. Paul to today’s West Duluth to set up a sawmill which was a start to the significant logging and milling operations that developed along the St. Louis River over the years.

The mid-1860s brought Philadelphia’s Jay Cooke to the community where he set out to build the Northern Pacific Railroad from Duluth to Seattle’s Puget Sound and the Lake Superior & Mississippi Railroad from St. Paul to Duluth. The Duluth Ship Canal was cut in 1871 and allowed the land west of Minnesota Point to develop into the world’s largest inland port at that time. With a railroad, a canal, and a safe port, Duluth sat poised to become a major center of commerce in the United States in the 1880s, including a major grain-trading center (Lydecker et al., 1976; Silberman, 1992).

In the late 1880s John D. Rockefeller, who had developed an earlier interest in shipbuilding by investing in the American Steel Barge Company, traded cash to the Merritt brothers for a significant interest in their fledgling mining and railroad operations after the mines on Minnesota’s Iron Range failed to produce a profit and stock values fell. By 1894 Rockefeller had purchased all interest in the operations, ensuring regional success.

During the early 20th Century, the Port of Duluth was, for a time, the busiest port in the U.S., surpassing even New York City in gross tonnage (World Port Source, 2017). As of 1905, Duluth was said to be home to the most millionaires per capita in the U.S. (Zenith City Archive. Brief History of Duluth, 1856–1939). In 1913, U.S. Steel built the community of Morgan Park in conjunction with the construction of a steel mill. The carefully planned company town was built for the families of the steel firm’s managers, supervisors, and skilled laborers and named for J. P. Morgan.

The net result of the era of development, prior to the adoption of environmental legislation in the 1970s, was substantial loss of aquatic habitat due to many years of dredging and filling the estuary to create the Duluth-Superior Port and the related problem of contaminated sediments. During this period an estimated 2,832 ha of aquatic habitat was dredged and/or filled (MPCA and WDNR, 1992). These habitat alterations took place prior to the adoption of our current environmental protection laws and rules. In addition, there was a long history of untreated or partially-treated industrial and municipal effluents directly being discharged to the St. Louis River.

These discharges and their legacy pollution were from days prior to adoption of current environmental protection laws and rules. With the advent of the Clean Water Act in 1972, the U.S.-Canada Great Lakes Water Quality Agreement in 1972, the Endangered Species Act in 1973, and the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) in 1980, a basic structure of pollution control, environmental regulation and remedial action was established that laid the groundwork for RAP planning to follow.

Onset of Remedial Action Plans in 1985 and the codification in the Great Lakes Water Quality Agreement in 1987

As noted above, in 1985 federal, state, and provincial governments committed to developing a RAP to restore all impaired beneficial uses in 42 AOCs and Minnesota took the lead on the St. Louis River AOC (Hartig and Thomas, 1988). The codification of RAPs in the 1987 Great Lakes Water Quality Agreement gave legitimacy to the process (Canada and the U.S., 1987). A 43rd AOC was identified in 1991 (i.e. Presque Isle Harbor, Pennsylvania, USA). By 1992, the Minnesota Pollution Control Agency (MPCA) and Wisconsin Department of Natural Resources (WDNR) had completed a Stage I St. Louis River RAP that was submitted to the International Joint Commission and U.S. Environmental Protection Agency (Table 1). This plan, which identified the legacy problems known as BUIs, was the culmination of years of work by a local citizen’s advisory committee and agencies. By 1995, this team had identified many priority actions that could be taken to address the impairments that were documented in the Stage II RAP (MPCA and WDNR, 1995). Among those recommendations was restoration of 688 ha of aquatic habitat.

Many of the actions identified in the Stage II RAP, in conjunction with prior major actions such as the development of the Western Lake Superior Sanitary District in the late-1970s, were funded and completed. For example, between 1978 and 2010 it is estimated that: approximately $320 million was spent on wastewater treatment improvements and infrastructure in Minnesota; $85 million was spent on contaminated sediment cleanup at Wisconsin’s Hog Island-Newton Creek and Minnesota’s St. Louis River Interlake Duluth Tar site; and $15 million was spent on acquisition and restoration of over 6,500 ha of habitat in Wisconsin. Although these efforts were commendable, only 103.2 ha of aquatic habitat had been restored (15% of goal) and there was not yet sufficient sediment data available to identify what sites required remediation. In June 2009, MPCA informed USEPA that based on available information the cost to clean up contaminated sediments was estimated to be $1.82-17.70 billion. It was clear that additional work was required further characterize contaminated sediments to better define and focus work required cleanup of legacy contaminants. Additional aquatic habitat restoration also needed to be defined to meet the restoration goals.

Business plan: Implementation framework and roadmap to delisting

In 2010, U.S. Congress established and funded the GLRI. This single action proved to be a catalyst to get work done across the Great Lakes. Congress identified the U.S. Environmental Protection Agency as the lead agency for the GLRI and the federal agency working group identified cleaning up and restoring AOCs as the number one priority in their plan. This was significant news for the St. Louis River AOC and others, considering it had spent over two decades on planning (Table 1).

The USEPA awarded a GLRI grant to the MPCA in late-2010 to fund the development of an updated RAP. This grant, in conjunction with a five-year commitment to fund staff capacity, was critical to the development of a strategic business plan for the St. Louis River AOC. This capacity funding allowed AOC coordinators and leaders from multiple organizations to work together in a concerted effort to complete a roadmap to delisting (LimnoTech, Inc., 2013a). AOC managers and leaders included representatives from the MPCA, WDNR, Minnesota Department of Natural Resources, the Fond du Lac Band of Lake Superior Chippewa, and the St. Louis River Alliance. This fully-funded effort marked the first time these groups had the capacity to sustain a focused and coordinated effort aimed at removing BUIs and delisting the AOC. The plan was formally accepted by USEPA in July 2013. The updated plan embodies four key attributes:

  • Inclusive – Developed with an extensive stakeholder involvement process with over 70 individuals from approximately 30 partner agencies, local units of government, research institutions, nongovernmental organizations, and stakeholder groups. Work completed by BUI teams and other supporting groups forms the basis of the Roadmap.

  • Comprehensive and Targeted – Contains targeted (i.e. specific and measurable) removal objectives, removal strategies, and ∼70 actions with deadlines and budget estimates.

  • Aggressive – The goal of the roadmap is delisting of the AOC by 2025 – which calls for completion of all major sediment cleanup and habitat restoration projects by 2020.

  • Timely – It allows the agencies and AOC partners to make the most of available funding sources that may not exist in the future, including GLRI and Minnesota Clean Water, Land and Legacy funding.

The St. Louis River AOC Implementation Framework: Roadmap to Delisting (Remedial Action Plan Update) is essentially a business plan that defines a reasonable and effective path forward to restoring the SLRAOC, so the legacy of the St. Louis River estuary can be redefined for residents and visitors in this generation and generations to come (LimnoTech, Inc., 2013a). The plan describes actions required to remove beneficial use impairments, establishes timelines for necessary actions, and identifies the budget necessary to accomplish delisting of the AOC.

In 2013, the draft budget and costs associated with implementation of the actions in the business plan were estimated to range from $300-$400 million (LimnoTech, Inc., 2013a). In addition, operational support from U.S. Environmental Protection Agency for AOC staff at MPCA, WDNR, Minnesota Department of Natural Resources, the Fond du Lac Band of Lake Superior Chippewa, and the St. Louis River Alliance was crucial for successful completion of the plan. It was made clear that this support must be stable and sustained, and that completion of this aggressive plan requires program staff positions to be maintained over the long-term without interruption.

Collaborative funding to implement priority actions: Minnesota water, land and legacy funds

In 2008, Minnesota's voters passed the Clean Water, Land and Legacy Amendment to the Minnesota Constitution to: protect drinking water sources; protect, enhance, and restore wetlands, prairies, forests, and fish, game, and wildlife habitat; preserve arts and cultural heritage; support parks and trails; and protect, enhance, and restore lakes, rivers, streams, and groundwater. Both MPCA and Minnesota Department of Natural Resources have utilized these resources to match federal funds to implement priority actions in the plan. This has included funding the necessary scientific work required to: document where work needs to be performed; funding a RAP Partnership Agreement with the U.S. Army Corps of Engineers to develop contaminated sediment cleanup and restoration site designs; and funding project work on the ground and in the water. In federal fiscal years 2010-2018, over $19 million of Minnesota Water, Land, and Legacy Funds have matched over $46 million in federal GLRI funds and $11 million in Harbor Maintenance Trust Funds. Indeed, Krantzberg and Rich (2018), Hartig et al., (1991) and Kellogg (1993) demonstrated that both cooperation and creative funding were key elements for success of RAPs.

Strategic partnership with U.S. Army Corps of Engineers: Engineering and design

In fall 2013, the MPCA and U.S. Army Corps of Engineers developed RAP Partnership Agreement to complete construction design and engineering work at Minnesota aquatic habitat restoration and contaminated sediment sites. This agreement has grown to an $8.1 million design agreement where GLRI has provided the U.S. Army Corps of Engineers with $5.3 million and the MPCA has provided $2.8 million in Minnesota Water, Land and Legacy Funds that will result in construction bid ready designs for aquatic habitat restoration and contaminated sediment cleanup projects that in total will cost in excess $100 million. This has been an extremely positive partnership and it is making wise use of the U.S. Army Corps of Engineers skill sets to meet urgent needs for getting work done in the St. Louis River AOC (MPCA, 2015a,b).

Aquatic habitat restoration design at 21st Avenue West and 40th Avenue West sites followed a biological, chemical, and physical design approach approved by MPCA and Minnesota Department of Natural Resources (MPCA, 2015c). Using a data-driven approach, the restoration work was designed to achieve least impaired condition metrics established for benthic community health (Angradi, et. al., 2017) and aquatic vegetation (Angradi et. al., 2013; N. Danz, University of Wisconsin-Superior, Wisconsin, in preparation).

The MPCA and U.S. Army Corps of Engineers are utilizing navigational dredge materials for aquatic habitat restoration and capping at contaminated sediment sites (U.S. Army Corps of Engineers-Detroit District, 2015, 2016, 2017). To maintain open shipping lanes in the largest working port on the Great Lakes, the U.S. Army Corps of Engineers dredges about 91,750 m3 of material out of the navigational channels on an annual basis. Historically, there have been barriers to placing this material back in the water. Minnesota and Wisconsin state agencies have historically denied U.S. Army Corps of Engineers’ requests to do so. When partners recognized that clean dredged materials were going to be needed to adjust the bathymetry at sites to restore aquatic habitat, a team at MPCA and U.S. Army Corps of Engineers embarked on an effort to identify what testing and what contaminant thresholds might be required to permit beneficial use of navigational dredge materials for aquatic habitat restoration. The result was the development of a technical paper entitled “Managing In-Water Placement of Dredge Material for the Habitat Restoration Sites in the St. Louis River Area of Concern” (MPCA, 2015b).

This has resulted in the use of the U.S. Army Corps of Engineers’ Operation and Maintenance Authority and Harbor Maintenance Trust Fund financing for the implementation of habitat restoration designs at two priority restoration sites in the St. Louis River AOC - 21st Avenue West and 40th Avenue West sites. When completed in 2019, more than 841,000 m3 of dredge material will have been beneficially used at these sites to implement aquatic habitat restoration design. The design and construction are 98% federally funded per an agreement with U.S. Army Corps of Engineers and USEPA under the GLRI Regional Working Group. The Harbor Maintenance Trust Fund financed $11 million of the final design and construction cost of $17.6 million for these two sites. This collaboration represents an effective and efficient method for achieving the joint U.S. Army Corps of Engineers’ and Duluth Seaway Port Authority’s goals of keeping the harbor open for commerce, while also meeting a Great Lakes Water Quality Agreement goal of removing impairments and delisting the St. Louis River AOC.

Great Lakes Restorative Initiative, Great Lakes Legacy Act and contaminated sediment cleanup in Minnesota

Contaminated sediment is a long-standing problem in the St. Louis River AOC contributing to a number of BUIs (Crane et al., 2002; Somat Engineering, 2012a,b; Weston Solutions, 2012a,b; RTI Laboratories, Inc., 2015). In 2002, USEPA’s Great Lakes Legacy Act was signed into law with the specific intent to expedite projects to remediate contaminated sediment in Great Lakes AOCs. The St. Louis River RAP identified 14 additional Minnesota contaminated sediment sites where sediments are contaminated with mercury, dioxins, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and other toxic substances (MPCA, 2015d; LimnoTech, Inc., 2013b, 2016a,b). Federal funds through the Great Lakes Legacy Act are now being used to leverage other funding sources to accelerate cleanup efforts and to will help communities fulfill the promise of economic revitalization, increased property values, and improved quality of life.

Cleanup activities at three sites in Minnesota have been completed. The Interlake Duluth Tar superfund site was completed in 2013, the Slip 2 site was completed in 2016 (cleaned up as part the development of Pier B Resort), and the Duluth Seaway Port Authority Garfield D slip was cleaned up through a Transportation Investment Generating Economic Recovery (TIGER) grant from U.S. Department of Transportation.

Ten of the remaining sites are being addressed through a unique collaboration among the MPCA, USEPA, and U.S. Army Corps of Engineers (Table 2). As described above, the U.S. Army Corps of Engineers is providing the technical and engineering skills through the MPCA-U.S. Army Corps of Engineers St. Louis River RAP Partnership Agreement to develop the designs for cleanup of the contaminated sediments at these sites. Teams of MPCA, USEPA, and U.S. Army Corps of Engineers staff are developing the designs and will oversee construction of the cleanup activities. In some cases, U.S. Army Corps of Engineers will contract for the construction and in others, USEPA will take the lead.

The funding for this work through the Great Lakes Legacy Act will include up to $47.2 million from GLRI through USEPA and up to $25.4 million from Minnesota general obligation bond funds that were appropriated in 2017 (Figure 2). The Minnesota Legislature also provided funding for four staff to manage this work through state fiscal year 2020. The projects are currently on track to be completed by 2020.

The other major Minnesota contaminated sediment site is the Spirit Lake Legacy Act Cleanup site, a section of the St. Louis River near Duluth. This is where the former massive Duluth Works steel plant operated from 1915 to 1972. The plant released a variety of pollutants into Spirit Lake, including PAHs and heavy metals, including lead, copper, and zinc. The USEPA and U.S. Steel have been working in partnership under the authority of the Great Lakes Legacy Act to develop a comprehensive plan to clean up contaminated sediment at this site. USEPA and U.S. Steel have thus far reviewed potential cleanup alternatives. They are proposing a combination of dredging, capping, and on-site disposal to clean up contaminated sediment in Spirit Lake. Their experts believe this proposed plan is the best way to manage potential risks to human health and the environment posed by these contaminated sediments.

Although design is not yet complete, it is estimated that this cleanup and restoration will cost approximately $75 million, with U.S. Steel providing $41.25 million and U.S. Environmental Protection Agency providing $33.75 million. Final design and permits for this project are expected by December 2018 and construction is scheduled to begin in September 2019.

Collaboration and funding lead to progress

It is fair to say that there is no simple or easy way to fund remedial actions in AOCs. Getting projects funded and completed, and removing BUIs, takes persistence, patience, tenacity, and creativity. The experience in the St. Louis River AOC has shown that key to success is development of the RAP as a strategic business plan which includes specific BUI related actions, specific timelines, and a budget that includes staff capacity and project cost estimates. This approach has led to success in identifying funds and achieving quantifiable progress.

For example, as of 2017, 99% of the priority actions identified in the St. Louis River RAP have either been completed or are in progress (MPCA and WDNR, 2017). Of the major Minnesota aquatic habitat restoration actions identified in the RAP: five have been completed; four are funded and in progress; and one is in design awaiting construction funding. Of the major Minnesota contaminated sediment actions, three have been completed and 11 are in the feasibility study/design or construction phase (Table 2).

In addition, many habitat projects have been implemented with collaborative funding. For example, between 2015 and 2020 nine habitat projects will have been completed, totaling 653 ha of habitat restored (Table 3). Funding for these St. Louis River habitat restoration projects is coming from GLRI ($15 million), Harbor Maintenance Trust Funds ($11 million), Natural Resource Damage Assessments ($5.5 million), and Minnesota Legacy Funds ($19 million).

Clearly, much has been accomplished, but only one BUI has been removed to date (i.e. degradation of aesthetics). However, following the roadmap to delisting (Limnotech Inc., 2013), the remaining eight BUIs are projected to be removed by 2025, contingent upon confirmation of use restoration via monitoring (Table 4).

Further, it must be recognized that there are vulnerabilities to such a collaborative financing approach. For example, there can be considerable challenges in trying to meet an implementation timeline for remediation and restoration projects because of the need to align financing schedules from different sources (due to different agency- and organization-specific requirements). Complications can also arise when there is a delay in a remediation or restoration project that affects the funding requirements of all funding agencies/partners involved. Implementation timelines are essential to increase accountability and sustain momentum. The benefits of such a collaborative financing approach can outweigh the risks; however, continuous and vigorous oversight, creative problem-solving, and flexibility are often needed to realize implementation of multi-partner remediation and restoration projects.

Concluding thoughts and lessons learned

The actions currently being undertaken in the St. Louis River estuary are part of a long history of land development, natural resource use and exploitation, and more recently recovery and restoration. Actions taken by the earliest users of the land had far-reaching effects that continue to shape the course of the estuary. The early phases of development in the estuary were dominated by independent, powerful agents of change who were primarily focused on accessing abundant natural resources and creating a place for people to live and work. More recent actions have had different drivers, with an emphasis on human and ecological benefits of the estuary and beneficial uses that have been impaired by the legacy of past practices. This new stage of development requires a more integrative approach that considers multiple uses and benefits, and a much broader array of stakeholders and cooperative financial commitments. The AOC delisting process is an important part of this trend, and provides a framework, not only for BUI removal, but also for creative, collaborative funding support for remediation and restoration actions.

The establishment of the GLRI and passage of the Great Lakes Legacy Act have been critical to the progress thus far in restoring the St. Louis River AOC and will be essential to removing all BUIs by 2025, contingent upon confirmation via monitoring, and then delisting as an AOC. Under the framework of the AOC delisting process and the GLRI and the Legacy Act, it was possible to develop collaborative funding and matching agreements to make sure that federal seed money leveraged resources from many other sources, including: the Minnesota Water, Land, and Legacy Funds (Clean Water Fund and Outdoor Heritage Fund), Minnesota Bond Funds, Water Resource Development Act Harbor Maintenance Trust Funds, and private sources.

The development of a bold and aggressive plan for collaboration and funding helped identify and leverage the financial resources required to implement all actions identified in the RAP. Between 2011 and 2017 approximately $57 million was raised and applied strategically toward restoration of impaired beneficial uses. Between 2018 and 2021 an additional $155–170 million will be needed to implement all necessary remedial actions identified in the RAP that will lead to potential delisting in 2025.

The collaborative planning and funding process that is taking place in the St Louis River AOC was enabled by the delisting framework and supporting funding sources at all levels of federal, state, and municipal government, as well as private entities and NGOs. Such a collaborative approach to planning and funding could be beneficial to other AOCs struggling to achieve necessary remedial and preventive actions to remove remaining BUIs.

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Note

Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uaem.