Feats of Engineering: St. Louis River Sediment Remediation ...

Posted: 1:40 pm Mon, September 10, 2012
By American Council of Engineering Companies of Minnesota?
Tags: Barr Engineering Co., Minnesota Department of Natural Resources, Minnesota Pollution Control Agency, St. Louis River sediment remediation

The 255-acre St. Louis River/Interlake/Duluth Tar site was cleaned up using one of the first ?hybrid? sediment remedies, which combined dredging and capping, surcharge capping, activated carbon mats, and a novel integration of remediation, mitigation and restoration. (Submitted photo)

Location: Duluth

Firm: ?Barr Engineering Co.

Editor?s note: The Feats of Engineering feature, which runs occasionally in Finance & Commerce, currently focuses on the grand award winners of the annual Engineering Excellence Awards Competition sponsored by the American Council of Engineering Companies of Minnesota. The winners involve projects completed between Nov. 1, 2009, and Oct. 31, 2011. The content comes from ACEC and the firms.

The 255-acre St. Louis River/Interlake/Duluth Tar Superfund site in Duluth is on a Lake Superior estuary and represents the largest sediment remediation project in Minnesota?s history. The site?s contaminated soils and tar seeps were cleaned up in the 1990s, but 90 acres of contaminated sediment proved more challenging and costly.

In 1999, the Minnesota Pollution Control Agency determined that all contaminated sediment must be dredged and transported offsite ? a remedy that would cost $140 million and created concerns about air and water impacts. To move the project forward, an independent peer-review team evaluated the site and recommended additional studies, which were conducted by Barr Engineering Co.?s staff members.

After the study, staff from Barr, the funders and the MPCA hosted a two-day exercise for 55 stakeholders to identify alternatives to sediment dredging, which resulted in a Barr-designed combination of dredging and more than 18 types of capping ? one of the nation?s first hybrid remedies.

A confined aquatic disposal area was constructed by building a rock dam between a 2,000-foot-long former shipping slip at the site and the St. Louis River to isolate the dredged contaminated sediments and create fish habitat and wetlands where there once was industrial shipping.

At Stryker Bay, a 40-acre shallow-water area, the Minnesota Department of Natural Resources preferred dredging to capping to maintain water depths for fish. However, dredging the very tarry material in an 11-acre corner of the bay would have created emissions exceeding air-quality limits at waterfront residences. Instead, Barr developed a surcharged cap that compressed the contaminated layers so a cap could be placed without reducing water depths. Over three years, the surcharge consolidated the sediments, making room for a permanent sand cap while restoring the shallow bay.

The surcharge also included the first commercial use of an activated carbon mat in sediment capping. The surcharge area was covered with activated carbon mats as a barrier between the sediment and the clean sand cap. As the sediment compressed, contaminated porewater flowed upward through the mats and activated carbon between permeable geotextiles adsorbed the contaminants. Sand added to the carbon layer helped the mats sink to the bottom, and a root barrier incorporated on top of the carbon now prevents access to the contaminants.

The project also integrated remediation, mitigation, and restoration to save time and money. For example, to mitigate the loss of water volume from capping activities, Barr oversaw dredging of approximately 60,000 cubic yards of clean sediment at a nearby bay to restore 16 acres of fish habitat. The dredged sediment was then pumped through a two-mile pipeline to the site for use as a top layer of the caps and covers to jump-start aquatic communities. Integrating mitigation and remediation saved more than $2 million.

Completed in 2010, the project protects human health and the environment and restored 106 acres of wetland and riparian habitat for fish and wildlife. Compared to an all-dredging approach, it saved Barr?s client $90 million.

To submit projects for consideration in Feats of Engineering, please email the following information to David Oxley, ACEC/MN executive director, at doxley@acecmn.org: firm name, project name, location and description; projected or actual completion date; firm project team and overall project team; additional details of interest to the architecture, engineering and design community; phone number and email address for a project. High-resolution renderings or photographs (minimum of 1MB) also should be submitted. For more information, call 952-593-5533.

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Source: http://finance-commerce.com/2012/09/feats-of-engineering-st-louis-river-sediment-remediation/

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