Post-dredging monitored natural recovery of surface sediments in an urban river

Purpose

Verification monitoring was performed over five years following the sediment remediation of the Buffalo River Area of Concern (AOC), New York, USA. Monitoring results were compared with surface sediment cleanup goals to determine whether natural sedimentation allowed the AOC to achieve long-term remedial goals without the placement of cover material to manage dredge residuals.

Material and methods

Monitoring was conducted two years and five years following sediment remediation and included: 1) bathymetric surveys to understand sediment stability and deposition rates, and 2) the analysis of surface sediment samples for four primary chemicals of concern (COCs), including polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), lead, and mercury, to compare surface sediment concentrations over time with site-specific sediment remedial goals.

Results and discussion

The monitoring results demonstrated the following: 1) sedimentation is occurring, 2) a stable depositional environment is present throughout the Buffalo River AOC, and 3) measurable reductions in sediment concentrations were observed for PAHs, PCBs, lead and mercury in the newly deposited sediment. By Year 5, surface sediment chemistry results generally achieved the remedial goals throughout the Buffalo River AOC.

Conclusion

Monitored natural recovery (MNR) was effective in physically isolating dredge residuals in the Buffalo River AOC, following sediment removal. This post-dredging MNR approach met the surface sediment remedial goals in most areas, resulted in a protective and cost-effective project by not requiring the placement of clean cover material in the dredge areas, and was an environmentally sustainable strategy by eliminating the need to collect, transport, and place millions of kilograms of clean quarried material in the river.