| Silt
Curtains Assist in Contaminated Sediment Removal Floating turbidity control curtains have been used since 1970 to control suspended silts generated by dredging and marine construction operations. Their use is intended to guard against adverse environmental impact to the area adjacent to the work site. Recently, silt curtains have been found to be useful during hazardous material or contaminated sediment removal operations in a marine environment. The following case history summarizes one project which utilized silt curtains. In 1995, after months of evaluation, a permit was issued to remove PCB laden sediments from a river in the vicinity of an industrial complex’s water discharge in upstate New York. The remediation project was headed by OHM Corporation. It involved the participation of Federal, State and Local agencies, engineers of the company and subcontractors, including American Marine, Inc. The remediation plan involved underwater surveys, which revealed the location of many large boulders in the contaminated area which would have to be removed. The plan proposed the use of state-of-the-art dredging techniques which were designed to keep disturbance and suspension of the sediments to minimum. A multi-stage sediment treatment process was to be set up on the owners property to “clean” the removed sediments. All of these processes had been granted a green light early on. At issue was the need to isolate the work area from the rest of the river to insure that no resuspended sediments created during dredging would spread downstream. The obvious plan was to employ silt control curtains to encircle the work area and control the release of any sediments which would find their way to uncontaminated areas downstream. State and Federal agencies were skeptical about the effectiveness of silt control curtains prior to this project. Curtains were attempted for a similar project on the St. Lawrence Seaway. A combination of improper installation, current and vessel traffic rendered the curtain useless. The silt curtain task for this new project was given to American Marine. They were to design a viable curtain and installation plan which would be effective. The silt curtains were proposed and the installation was approved and permits were issued. American Marine installed a system consisting of three silt curtains, two of which were parallel to one another approximately 10 feet apart. They formed the outer perimeter of the work area. The Inner and Outer curtains as they were labeled, incorporated a reefing system which allowed workers to keep the curtain bottoms within prescribed distances off the bottom of the river. The curtains were arranged in a semi-circle starting well upstream of the dredging area where they were anchored of the river bank. They were then deployed into the river, side by side, at a slight angle to the current so that they tended to deflect the river water flow. This orientation of the curtains to the normal flow of the river greatly reduced any tendency of the flow to overload the curtains or raise their ballast chains. The third curtain was utilized inside the two perimeter curtains to locally isolate the immediate area in which the dredge was operating. American Marine personnel were present and handled all curtain installation, movement and removal during the project. The curtains were delivered and installed by American Marine in June 1995. They remained in place until the end of dredging operations in September. The silt curtains performed their purpose successfully. Despite dredging techniques designed to limit sediment resuspension, turbidity levels inside the curtains were high. Constant monitoring outside the curtains revealed no unacceptable release of sediments. The American Marine Silt Control Curtains had performed as expected. The result was a renewed acceptance of silt curtains as an effective tool to isolate a contaminated sediment removal. It was proven that with sufficient site-specific information, a determination can be made if silt curtains will be viable. Secondly, if the curtains are designed properly and manufactured to strict quality standards, the remediation contractor can rely on their performance. And finally, if a well planned installation scheme is employed, then silt curtains will be effective. |
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