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USACE Detailed Sediment Investigation Rices Point

The sediment investigation was performed around two separate areas within the mouth of the St. Louis River in Duluth Harbor, Minnesota; Rice’s Point and Hearding Island.  The harbor is separated from Lake Superior to the east by Minnesota Point, a long peninsula that extends south from Duluth, MN to Superior, WI.  The areas on both the northern Minnesota side and the southern Wisconsin side of the river are highly industrialized in the area of the harbor.  Freighters using the St. Louis River serve as the primary method of transport for industries that include steel making, grain storage, and cement powder shipping.

Somat Engineering, Inc. was retained by the U.S. Army Corps of Engineers-Detroit District (COE) to perform the Detailed Sediment Investigation at the mouth of the St. Louis River in Duluth, Minnesota. 

The purpose was to characterize sediment material in the St. Louis River and Duluth Harbor, specifically in and around Rice’s Point and Hearding Island for the purpose of delineating the magnitude of contamination areas along the Minnesota shore line.  The data obtained during the investigation will be used and incorporated by both the COE and Minnesota Pollution Control Agency (MPCA) as part of a larger effort to establish a baseline understanding of sediment contamination throughout Duluth Harbor.

The investigation was performed in two phases.  The first phase of the project plan deployed a Laser Induced Fluorescence (LIF) survey tool to reveal qualitative information on the presence of polynuclear aromatic hydrocarbons (PAHs) in real time in the sediment.  The LIF instrument was advanced at over 180 locations to a depth at least three feet below the last positive instrument reading.  A geoprobe on a barge was used to deploy and advance the LIF.  The results of the LIF information were reviewed by MPCA and formed the basis of selecting the location of the sediment cores.

The sediment core samples were submitted to COE approved laboratories to be analyzed for various chemical and geotechnical parameters including polychlorinated biphenyls (PCBs), metals, diesel range organics (DRO), total organic carbon (TOC), semi-volatile organic compounds (SVOCs), grain size and dioxins.


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