A.22 Grasse River, NY (hotspot removal)

A.22.1 Summary

Environment:	Marine
Scale:	Full
Contaminants of Concern:	PCBs: 12–11,000 ppm prior to dredging
Final Remedy:	Hot spots were removed using hydraulic dredgingDredging by use of a large suction pipe mounted on a hull and supported and moved about by a boom, a mechanical agitator, or cutter head which churns up earth in front of the pipe, and centrifugal pumps mounted on a dredge which suck up water and loose solids. assisted by a diver with a vacuum dredge in the shallows. Dredge material was deposited in an existing on-site TSCA/RCRA landfill.

A.22.2 Site Description

Fresh water: 10–15 ft deep

Year: 1995

Contaminated sediment area of one-acre near shore.

A.22.3 Remedial Objectives

• Remove as much sediment as practical within an area bounded by a 10 ppm isopleths that would result in a 25% reduction in PCB mass.
• Dredge depth: 0-2 ft

A.22.4 Remedial Approach

• SWAC was used.
• A hydraulic auger dredge was used along with diver assisted vacuum dredging in shallows. Floating oil booms and three silt curtains (an outer, inner secondary and one for near shore boulder zone) were used.
• Silt curtains were hung to contain suspended sediment but sampling outside the curtains showed increases in concentrations.
• Surface sediment residuals PCBs ranged from 1.1–260 ppm after dredging.
• An undetermined amount of rocky debris on site made dredging difficult.

A.22.5 Monitoring

Resuspension occurred during the dredging operation. No details on resuspensionA renewed suspension of insoluble particles after they have been precipitated. controls for this site. Most activities were performed at extreme low tide. Sheet piling was used to withhold water from the dredging areas.

RAOs/project objectives achieved? Fish studies performed postdredging showed that fish PCB levels were 20–50 times higher immediately after the dredge action. These levels reduced to pre-removal levels three years after removal event. Sediment sampling following removal indicated levels decreased from 518 to 75 ppm in the top foot and from 1,109 to 75 ppm in all depths. 85% of projected mass was removed.

A.22.6 References

Alcoa, U.S. EPA. Superfund Program Update for the Grasse River Study Area. Jun 2004. http://www.thegrasseriver.com/pdf/Final_June_2004_Newsletter.pdf.

Major Contaminated Sediment Sites Database; Sept. 2004 as updated 2008. http://www.smwg.org/MCSS_Database/MCSS_Database_Docs.html.

Publication Date: August 2014