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St. Lawrence Remediation Considered “One of the More Successful in the U.S.”

This project was the subject of a number of presentations at Dredging ’02 in Orlando, May 5 through 8. Present were representatives of Bechtel Environmental, Inc., Metcalf and Eddy, and BBL, Inc. Marcus Faust, president of Faust Corporation, Ray Bergeron of Cable Arm Clamshell, and Lyman Burk, who provides the WINOPS software, were also present. This article is composed of material from personal interviews and the talks given at that conference. Proceedings of Dredging ’02 are available from the ASCE, www.pubs.asce.org.

Faust Corporation moved a fleet of dredges and support equipment from their headquarters near Detroit to the St. Lawrence River near Massena, New York in the spring of 2001.

The objective was to remove about 65,500 cubic meters (77,000 cubic yards) of contaminated sediment from the St. Lawrence opposite the former Reynolds Metals Company St. Lawrence Reduction plant.

The dredging began in April 2001, when the area was isolated by a 3800-foot-long sheet pile wall. Faust’s equipment working inside the wall included the derricks Comanche, a Link-Belt 318; and Relief, a Link-Belt 418; a Cat 350 excavator on a sectional barge, and the #4, a Clyde clamshell dredge leased from Ryba Marine. Support equipment included four tugs, two push boats, a 650 hp moulded bow tug, a 150 hp boat to manage the service barge, and two survey boats. The service barge was a general purpose vessel for such duties as oil changes, storing cable, and maintaining the air bubbler and silt curtains.

Alcoa Aluminum inherited the highly-contaminated site when it purchased Reynolds Metals. Reynolds was under administrative order by the U.S. Environmental Protection Agency and the New York Department of Environmental conservation to remove the contaminants and remediate the site, and Alcoa took over the project. In addition to phoychlorinated biphenyls (PCB’s), the site contained polyaromatic hydrocarbons (PAH’s), and dibenzofurans. PCB concentrations ranged from below detection limits to more than 2000 parts per million. The affected area occupied a half-mile stretch of the St. Lawrence River, with water depths from zero to 20 feet.

Faust used Cable Arm Environmental Clamshell buckets for dredging, which allowed precise removal of material while causing minimal turbidity. Each bucket was equipped with depth sounders, pressure transducers and pressure switches that located the bucket precisely in the water column and allowed the operator to see if the bucket was closed. WINOPS dredge positioning software interfaced the bucket data with global positioning system (GPS) data from receivers on the crane boom and the barge, tide gauges and bathymetric data for real-time monitoring and archiving of all data in electronic format. The progress of the work was posted daily on a website that could be accessed by the public.

This system preserved the history of all 38,146 buckets of material that were dredged, and allowed for verification of the dredged footprint, depth of contaminants removed, and volume of sediment removed.

The dredging area comprised 12 hectares adjacent to the main shipping channel, and was divided into 268 dredge cells. Sediment verification samples were collected after each dredge pass. The cleanup goal was 1 ppm of PCB’s remaining after the second dredge pass, and the results of the samples determined whether the cells had been remediated or if they required additional dredging.

Metcalf and Eddy, Inc. developed a flow logic sheet that analyzed the change in concentrations with each dredge pass and provided a definition that established an end point to dredging when the goals were not obtained. This allowed dredging to continue, while identifying areas that needed capping or other treatment.

Once Faust had his equipment on site, he was required to hire crew from local unions, none of whom had experience operating dredges, said Jeff Cange of Bechtel. One worker who applied to operate a dredge was a professional plasterer. Training these workers changed the scheduling of the project, and not all the workers were receptive to the training, so the operation of the project began less efficiently than expected. However, despite labor problems and cost overruns, the project was performed for $40,092,000, an under-run of $908,000, and completed on schedule in October, 2001. The sheet piling was removed in November, and a small amount of capping remained to be done in the 2002 dredging season.

Cange described factors that contributed to cost overruns, which were mainly in the construction of onshore sediment storage and handling areas, environmental monitoring, sediment processing, demobilization and construction management. These were because of problems in obtaining the required cleanup goals for sediment, which prolonged the project and led to more dredging, unexpected complications regarding sediment handling and processing; and the need to expand the scope of environmental monitoring in response to regulatory and stakeholder concerns.

The increased costs were offset by underruns for the sheet pile wall and silt curtain installation, dredging operations, onsite landfill operations, and the offsite shipment of sediments. There were smaller quantities of the more highly contaminated sediment that required offsite disposal than expected, said Cange.

Costs of removing and processing the contaminated material were broken down as follows:
Dredging: $143 per cubic meter
Processing: $144 per cubic meter
Offsite disposal: $144 per cubic meter
Onsite disposal: $28 per cubic meter (mostly material of 10 ppm or less)
Monitoring: $48 per cubic meter
Engineering: $105 per cubic meter
Total: $612 per cubic meter, or $2000 per pound

Cange estimated that 9180 kg (20,197 pounds) of PCBs were removed from the river, at a rate of $4367 per kg ($1985 per pound)

This could be considered one of the more successful environmental dredging projects completed in the United States, said Cange. There were no lost time accidents or injuries, even though at its peak there were two 10-hour shifts per day, employing more that 150 workers engaged in a multitude of dangerous tasks.