Predicting Release of PCBs at Point of Dredging

Abstract

A simple laboratory test, referred to here as the dredging elutriate test (DRET), was sought to predict the concentration of contaminants in the water column at the point of dredging. The DRET is procedurally similar to the modified elutriate test developed by the U.S. Army Corps of Engineers to predict concentrations of contaminants at the point of disposal of dredge material. The objective of experimentation was to investigate the release of dissolved and suspended polychlorinated biphenyls (PCBs) as a function of initial concentration of sediment, aeration time, and settling time in the DRET. Settling time was found most important. Field data from a pilot dredging project if New Bedford Harbor, Mass. compared well to results of the DRET. Most of the PCB in the field and DRET were sorbed to small particles rather than dissolved. A good correlation was obtained between total PCB and total suspended solids. A sorption equilibrium model based on available partition coefficients described the sorbed-dissolved PCB distribution. Particle size distribution analysis showed that the mean diameter was less than 10 μ\Nm after just 0.5 h of settling and decreased very little with further settling. These particles and their PCB burden have the potential to be transported away from a dredging site.