Point of Beginning - March 2010 - (Page 12)

eginning around 1800 and continuing until the economic recession of the 1970s, Duluth, Minn., was one of the most active industrial areas in the United States, particularly during the world wars. Coking plants, coal refiners, tar manufacturers and similar heavy industries were concentrated on the banks of the St. Louis River, where they could take advantage of extensive shipping facilities. The region’s manufacturing legacy left quite a mark on the river. Contaminants and wastewater were discharged more or less continuously for about 170 years; in the ’70s and ’80s, it was common to see tar and oil oozing to the surface of the shallow wetlands and man-made peninsulas that characterize the area. Subsurface analysis revealed a stew of toxins, including residual tar chemicals, polycyclic aromatic hydrocarbons, volatile organic compounds, cyanide, naphthalene and heavy metals like mercury. Today, the formerly active manufacturing area is called the St. Louis River/Interlake/Duluth Tar Superfund Site (SLRIDT Site). The 1983 Superfund designation allowed the Environmental Protection Agency (EPA) to identify responsible parties and use federal funds for cleanup. Remediation began in 1992 and continues today. However, SLRIDT Site remediation has been complicated by several natural processes, including currents, waves and freeze/ thaw cycles. Over time, chemicals mixed and worked their way deeply into the wetland soils. Dredging and removal of the top layers, now largely complete, was effective, but no amount of removal could totally eliminate the toxins. Therefore, the remediation strategy included “capping,” a process through which layers of relatively impermeable soils and/or geotextile barriers are placed over contaminated soils to keep them in place, even when exposed to current and wave action. Done properly, capping can also prevent roots, burrowing animals and invertebrates from reaching the contaminated soils beneath. The specific capping strategy employed by the projects’s general contractors, which included The Shaw Group as prime contractor, was a “three-layer cake” of dolomite, a geotextile root barrier and a top layer of red sand. To work as intended, coverage had to be consistent and thorough. To achieve this goal, Marine Tech LLC, marine construction subcontracPhoto courtesy of Barr Engineering IT] ID ON AL [PUT in ork seals ds. yw eful sur ve otects wetlan Car ins and pr tox BY ANGUS W. STOCKING, LSMARCH 2010 | Point of Beginning | www.pobonline.com http://www.pobonline.com

Table of Contents for the Digital Edition of Point of Beginning - March 2010

Point of Beginning - March 2010
Contents
Editor’s Points
Newsline
Put a Lid on It
Safe Passage
Changing the Channel
‘Capturing’ the Mighty Mo
Traversing the Law
Surveying GIS
Safety Sense
New & Notable
Classified Ads
Fun & Games
Ad Index

Point of Beginning - March 2010

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