Theoretical Evaluation of the Effectiveness of Capping PCB Contaminated NewBedford Harbor Bed Sediment

摘要

The report contains two separate studies of the contaminated bed sediment in theUpper Estuary of New Bedford Harbor, Massachusetts. One is concerned with determining the flux of polychlorinated biphenyls (PCBs) from the bed to the water column. The other is concerned with the general theory of capping a contaminated bed with clean soil/sediment to isolate the pollutants from the water column. Three approaches were used to establish the PCB flux. Since direct methods are impossible three modeling approaches were used: (1)bed-sediment dissolution model; (2)overall estuary mass balance model and (3)flow-by-concentration model. The common region of overlapping rates for the three models is 1700 to 3300 kg/y. Three principles were identified based on changes brought about in transport mechanisms increased path length and chemical equilibrium that render capping an effective technology for isolating contaminants from the water column. Theoretical mathematical models were developed to investigate breakthrough time and steady-state flux of PCBs through the cap. For a 45 cm. thickness the time is 900 to 4500 years. The steady-state flux is reduced by 99.9%(+) for rates of 200 to 270 g/y of PCB from the Upper Estuary Bed. The above numerical values are theoretical estimates.