Excessive PCBs in the Hudson River: Attributable to Incompleteness of Dredging, or to Seven Years of Dredging?

Abstract

ABSTRACTGE recently completed a seven-year US EPA-mandated clamshell dredging project to remediate PCB contamination of the Hudson River. Post-project PCB levels in water and fish, however, are higher than anticipated, suggesting to some the need to extend the project to remove more PCB-bearing sediments. Our investigation of the effectiveness of the dredging project revealed that a previously unconsidered physical process must mobilize sediments as a result of dredge bucket closure. We also used computerized dredging data (‘bucket files’) to estimate the fraction of dredged sediments returned to the river instead of being deposited into waiting barges. We conclude that excessive post-project PCBs in the Hudson River predominantly are attributable to sediment mobilization by clamshell dredges. We predict that proposed extension of the dredging project would prolong mobilization processes, allowing PCBs to spread widely and enter ecosystems that include people, endangered fish such as sturgeon, and endangered birds such as bald eagles.