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Evaluation of Sediment Agitation and Mixing Into the Surrounding Water Column From Capping Activities – Boston Harbor
Citation:
BATTELLE. Evaluation of Sediment Agitation and Mixing Into the Surrounding Water Column From Capping Activities – Boston Harbor . U.S. Environmental Protection Agency, Washington, DC, EPA/540/R-05/014 (NTIS PB2006-114554), 2004.
Impact/Purpose:
to publish information
Description:
Capping is a common remediation technology for the containment of contaminated sediments. While capping is a common remediation technology for contaminated sediments, little information exists on the potential release of contaminated sediments during and after the capping operation.
The U.S. Corps of Engineers (COE) performed capping operations on two confined aquatic disposal (CAD) cells that had earlier been excavated in the Boston Harbor/ Mystic River and filled with contaminated sediments. Every twelve hours a hopper dredge ship would spread clean dredged material over the targeted CAD cells. While COE capped the consolidated contaminated sediments, U.S. EPA/ORD sampled the surrounding water column for TPH, PAR, PCB, and RCRA metals. Sampling was conducted with a continuous flow towfish which also took continuous measurements of several water parameters, including depth, temperature, salinity, DO, and turbidity.
Analytical results of water samples collected before, during, and after capping activities were compared to quantify changes in contaminant concentrations in the water column caused by the capping activities. Three-dimensional maps were generated to show turbidity and contaminant levels in the areas where the capping took place. Findings indicate a significant increase of total PAR concentrations for CAD Cell M-19 from pre run concentrations with diminishing amounts of resuspension with successive layering. The final capping run demonstrated that the resuspension concentrations had returned to pre-survey concentrations. A similar resuspension scenario was demonstrated for PCB concentrations when compared to pre run concentrations. Resuspension concentrations in CAD Cell M-8 were generally lower than Cell M-19 but showed the same trends. Plotting contaminant concentrations against turbidity levels was not successful in determining whether areas of high turbidity (caused by capping) corresponded to areas of relatively high contaminate resuspension. Resuspended contaminated sediment traveled downstream with the current and dissipated within hours after capping activities ceased.