Formatted Title:

Using a Phased Approach to Evaluate Potential Ongoing Sediment Contamination in the Lower Clinton River Area of Concern

Background/Objectives:

The Clinton River Watershed comprises the Clinton River Area of Concern (AOC). The Lower Clinton River AOC Project site is located in Harrison Township, Macomb County, Michigan. The project site extends from Mount Clemens to the mouth of the River at Lake St. Clair and includes the entire ~7.5-mile Federal Navigation Chanel. The hydrology of the Lower Clinton River is impacted by the Clinton River Spillway and channelization/shoreline modifications at the mouth of the river.

U.S. Environmental Protection Agency (EPA) and Michigan Department of Environment, Great Lakes, and Energy (EGLE) entered into a Great Lakes Legacy Act (GLLA) Project Agreement to address polychlorinated biphenyl (PCB)-contaminated sediments in the Lower Clinton River. Site characterization results identified areas of PCB contamination both outside and inside the navigation channel between River Mile 3 and approximately River Mile 7. Remediation of the contaminated sediments is expected to contribute to the removal of the fish consumption and the restrictions on dredging BUIs.

As required by the GLLA, the Clinton River sediment remediation project cannot be implemented if the area is likely to suffer from significant further or renewed contamination from existing sources of pollutants causing sediment contamination following completion of the project (hereafter referred to as existing PCB source).

Sediment results suggest there may be an existing PCB source impacting the area of the river targeted for sediment remediation. Elevated PCB concentrations have recently been observed in surface samples collected from inside and outside the federal navigation channel, despite the fact that the federal navigation channel in this area was dredged in 2008 and 2009. The source or sources of contamination are unknown, however, a historical landfill on the north side of the river may be a potential PCB source within the targeted remediation area. Therefore, a source investigation is needed to fully investigate potential contamination sources and whether they pose a risk of recontamination in the project area.

Approach/Activities:

To evaluate the potential PCB source, a phased approach is being developed to take advantage of early-phase results to inform later phases of the investigation and build an accurate conceptual site model for the project area. In 2019, PCB congeners in the water column and recently deposited sediments were measured using passive samplers (semi-permeable membrane devices [SPMDs]) and sediment traps. The existing data from that effort and previous sampling are being analyzed to estimate PCB partitioning between sediment and porewater to further refine whether the sediments or water column are acting as PCB sources within the system. Following these analyses, remaining data gaps will be identified and later phase source evaluation efforts will be designed and targeted to address specific gaps.

Results/Lessons Learned:

The current efforts including results from passive samplers and the partitioning assessment will help refine the conceptual site model for the Lower Clinton River project area. This will support identification of existing PCB sources that, if not addressed, could potentially re-contaminate the river following remediation. Future phases of the source evaluation will fill data gaps and enable decisions to optimize the remediation footprint and approach.

Sam Noffke

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(Group 2, Poster Board #23) Using a Phased Approach to Evaluate Potential Ongoing Sediment Contamination in the Lower Clinton River Area of Concern