Alternative Technology for Sediment Remediation

Abstract

Duluth-Superior is a major port of the Great Lakes located at the extreme southwest end of Lake Superior in the cities of Duluth, Minnesota and Superior, Wisconsin. The harbor area occupies roughly 32 square miles and has 100 miles of waterfront. The harbor and lower St. Louis River have a history of water quality problems resulting primarily from municipal and industrial discharges in and upstream of the harbor. As a result, the harbor has been listed by the International Joint Commission as an Area of Concern (AOC) within the Great Lakes ecosystem. The 1995 progress report on the Remedial Action Plan (RAP) for the area identified sediment contamination as the major cause of many impaired uses in the St. Louis Estuary. Contaminants of concern include ammonia nitrogen, phosphorus, metals, oil and grease, PCBs, and PAHs. Contaminated sediments are thought to have detrimental effects on water quality, the diversity and abundance of aquatic and benthic organisms, human health, and disposal options for material dredged during harbor maintenance. The dredged material is stored in the Confined Disposal Facility (CDF) at the Erie Pier in Duluth. The CDF is nearing its capacity, and additional space is required for storage of dredged materials either by construction of a new facility or by extending the life for the one currently used. The Coleraine Minerals Research Laboratory (CMRL) of the Natural Resources Research Institute (NRRI) has, in the past, conducted several research programs to evaluate the construction of a sediment treatment plant at the Erie Pier CDF as an effective way of extending its life. CMRL is currently contracted by the US Army Corps of Engineers (ACE) to develop and engineer a plant to treat the sediment contained in the CDF. This study is being conducted in response to Section 541 of the Water Resource Development Act of 1996, initiated by Congressman Jim Oberstar, which states: "The Secretary shall develop and implement methods for decontamination and disposal of contaminated dredged material at the Port of Duluth, Minnesota". Various agencies including USEPA, Minnesota Pollution Control Agency (MNPCA), and NRRI conducted numerous research and survey projects. The sediments in the federal channels were analyzed as part of Dredged Material Management Plant (DMMP), and analyses revealed that metal concentrations in the sediments of all management units were comparable to those found in the regional soils, and that PCBs, pesticides, and PAHs were generally non-detectable. No PCBs and only low levels of PAHs were found in a survey study in Erie Pier CDF conducted by NRRI in 1997. Due to its relatively low contamination level, it is safe to study a number of variables before implementation of the technology to the other highly contaminated areas. The treatment plant should generate data on the effectiveness of using mineral processing technology for separation and decontamination of the sediments. In some cases, the separation products could be cleaned and used for other purposes such as brick manufacturing, landfill cover, beach nourishment, construction fill, and/or habitat enhancement.