Cumberland Bay PCB Sludge Bed Removal

Plattsburgh, New York

Date of Execution: April 1999

Significant Project Features:

• Hydraulic dredging and mechanical dewatering of 150,000 cubic yards of PCB contaminated sediments.

• Shoreline excavation of 38,000 cubic yards of PCB contaminated sediments.

• Installation of 1,000 linear foot steel sheet piling wall to isolate dredge area and to contain turbidity. Sheet piling driven in water up to 30 feet deep.

• Design, construct, operate and maintain a separation and water treatment train for a 2,000 gpm flow rate.

• Wide variances in bay bottom topography posed special dredging challenges.

History and Location of Project

The Cumberland Bay site is located in the northwest corner of Cumberland Bay in Lake Champlain, east of the city of Plattsburgh, Cinton County, New York. The sludge bed was composed of wood pulp, wood chip debris, fine organic matter, and other processing wastes that were discharged from local wood product industries (sawmills, wood chip producers, and paper manufacturing and processing). Untreated waste disposal ended in the early 1970's when the municipal sewage treatment plant began treating process wastes. Testing of the sludge bed materials conducted from 1992 through 1994 confirmed the presence of PCBs, dioxins, furans, and other contaminants. The high level of PCBs, which had been detected as high as 1,850 ppm in the sludge, pulp, and fine wood debris was the major concern at this site.

In 1999 the NYSDEC awarded Sevenson Environmental Services, Inc. a $23 million contract to dredge the sludge bed and to treat and dispose of the dredge spoils.

Description of Work

Work on the project began in April 1999. After the construction of extensive support facilities, including a 2,000 gpm WWTP to treat filtrate from the liquids/solids separation, Sevenson began work in the bay itself. Sevenson installed a 1,000 linear foot steel sheet wall to enclose an area of the bay known to contain the highest concentration of PCB sediments. This wall sheltered the area from prevailing wave action and thus prevented disturbance to the sludge bed.

The liquids/solids separation system consisted of sludge slurry storage tankage (400,000 gallons capacity) and pipelines (approximately 10,000 linear feet of 6" - 12" steel pipe) and eight plate and frame filter presses with 220 cubic feet capacity each. The water treatment system (2,000 gpm) consisted of modu-tanks, sand filters, and carbon filters.

Sevenson used one (1) H+H 12" dredge and one (1) H+H 10" dredge to perform all dredging. The 12" dredge is rated at 2,200 gpm, the 10" is rated at 1,800 gpm.

Dredge spoils were piped initially to shakers and desanders and then to storage mix tanks before processing through recessed-chamber plate and frame presses. All filtrate and water produced by the system was processed through a waste water treatment plant designed and operated by Sevenson. Treatment consisted of secondary settling, pH neutralization, oxygenation, and sand and carbon filtration. Approximately 160 million gallons of water was treated over the course of the project. Filter cake was stockpiled on containment pads in piles representing 8 hours of production. Each 8 hour pile was analyzed for PCBs, paint filter and percent solids. The piles were then shipped off site to either a TSCA (>50 ppm PCB) landfill or a non-TSCA (<50 ppm PCB) landfill.

Sevenson also used conventional track excavating equipment to excavate 38,000 cubic yards of contaminated sediments from near shoreline areas. Sediments excavated from the near shoreline area was stored in 100 cy piles. Samples taken from these piles were analyzed for PCBs, paint filter and percent solids. The piles were then shipped off site to either a TSCA(>50 ppm PCB) landfill or a non-TSCA (<50 ppm PCB) landfill.

Site restoration included removal of all temporary facilities, wetland re-establishment in the shoreline excavation areas, and grading and revegatation of all other disturbed areas.

<- Back to: Project Listings