A.9 Detroit River, Black Lagoon, Trenton, MI

A.9.1 Contacts

Regulatory Contacts: Great Lakes National Program Office and Michigan Department of Water Quality

A.9.2 Summary

Environment:	Off-channel freshwater embayment
Scale:	Full
Contaminants of Concern:	PCBs, oil and grease, mercury, heavy metals
Final Remedy:	Dredging and placement in Pointe Mouille Confined  Disposal Facility
Expected Recovery Time:	30 years

A.9.3 Site Description

The Black Lagoon is a small off-channel embayment located within the Trenton Channel of the Detroit River. The site is located adjacent to Mary Ellias Park in Trenton, MI. The site is located within the Detroit River Area of Concern (AOC). The Detroit River AOC is a binational AOC which drains approximately 700 square miles of land in Michigan and Ontario, including the city of Detroit, MI. Primary sources at this site include historical contamination from upstream industries.

The McLouth steel mill, located approximately one-half mile north of the site, closed in 1995 and is considered the primary source of sediment contamination in the Black Lagoon. CSOs, municipal and industrial discharges, and stormwater runoff may also have contributed to sediment contamination within the Black Lagoon. These impacts included the lagoon’s reduced capacity to support recreational activities such as swimming, fishing, and boating, as well as impairment of lagoon aesthetics from oil floating on the water surface. The health of the aquatic life in the water and sediments of the Black Lagoon, as well as wildlife along the shoreline, also were adversely affected by the pollution. The Black Lagoon proposal was the first project to be accepted and funded under the Great Lakes Legacy Act (GLLA) of 2002.

A.9.4 Remedial Objectives

Elevated levels of PCBs, mercury, and oil and grease were determined to pose a risk to the health of the benthic community. Two primary remedial objectives were established: 

• Reduce relative risk to humans, wildlife, and aquatic life.
• Restore the aquatic habitat within the Black Lagoon.

A.9.5 Remedial Approach

Final selected remedy: dredging followed by off-site disposal in a confined disposal facility.

Dredging was selected because a suitable disposal site was available and to facilitate revitalization of the off-channel embayment and adjacent upland properties. Because this work was completed under the GLLA, a feasibility study was not performed.

Dredging operations were undertaken with the goal to dredge to hardpan across the lagoon. Prior to dredging, a silt curtain was installed to enclose the entire lagoon and protect the adjacent river from releases of suspended sediments during dredging operations. Using a clamshell dredge device, approximately 103,500 yd³ of contaminated sediments were removed. After completion of this first round of dredging, the remaining residual sediments were sampled and analyzed to verify that the dredging activities reduced contamination to acceptable levels. Results of these analyses suggested that high concentrations of the contaminants of concern still remained in some areas, so a second phase of dredging (Phase II) was conducted to remove an additional 1–3 ft of sediment.

Sampling after Phase II of dredging indicated that, although contaminants were still present in some areas above originally targeted levels, the second round of dredging successfully reduced both the overall concentration and the distribution of those contaminants. In all, approximately 115,000 yd³ of contaminated sediments containing approximately 478,000 pounds of PCBs, mercury, oil and grease, lead, and zinc were removed from the lagoon. After removing the contaminated sediments, a sand and stone cover was installed. The cover consisted of at least 6 inches of clean sand that was further covered by 4 to 6 inches of stone. The primary purpose of the cover was to provide a barrier between the benthic community and any residual contaminated sediment. This cover will enhance natural attenuation, add habitat for regrowth of healthy organisms on the lagoon floor, and reduce exposure of fish to contamination through consumption of bottom dwelling organisms.

A.9.6 Monitoring

The original plan was based on the assumption that dredging activities would remove all or most of the sediments, and along with them, all or most of the contaminants of concern. The contaminants of concern, however, were still present at high levels after the first round of dredging operations. These higher than expected concentrations, along with deeper than expected post-dredge sediment depth measurements, confirmed suspicions that the original sediment depth estimates were incorrect. After reviewing the new sediment depth and contaminant data, a second phase of dredging was deemed necessary and samples were collected based on new criteria. Results suggest that, although the Phase II dredging activities did not completely reduce contaminant concentrations to the levels targeted, the second round of dredging was successful in reducing both the overall concentration and the distribution of those contaminants.

Although dredging efforts in the Black Lagoon dramatically reduced the levels of contamination across the site, the target cleanup levels were not achieved. As a result a residual cover was installed to isolate any remaining contaminated sediments. The residual cover consisted of at least 6 inches of sand and 6 inches of gravel installed to trap the underlying sediment and provide a clean habitat for benthic communities. After the deposition of the sand layer, 18 additional sediment confirmation samples were collected. Sampling in the sand cover is an environmental verification technique that is kept to a minimum, to maintain the residual cover’s integrity and prevent mixing the underlying sediment with the clean cover.

Expected recovery time: 30 years

Costs: The $8.7 million Black Lagoon remediationThe act or process of abating, cleaning up, containing, or removing a substance (usually hazardous or infectious) from an environment. project was funded with $5.6 million from GLNPO under the GLLA and $3.1 million in non-federal matching funds from the MDEQ.

The project successfully leveraged GLLA funding to complete a sediment cleanup. Although generated residuals prevented attainment of the target cleanup levels, the placement of a sand cover allowed the overall project objectives to be met. The project then served as a catalyst for site redevelopment. Subsequent to completion of the removal action, the City of Trenton was awarded $151,000 for shoreline habitat restoration. In June 2007, the City of Trenton received a $582,000 boating/infrastructure grant from the U.S. Fish and Wildlife Service for marina construction/boating access and is matching that grant with $200,000 to construct floating docks and boat access at the site.

RAOs/project objectives achieved? Through dredging and placement of the residual cover, the project objectives were achieved. In 2007, the City of Trenton and its many partners celebrated the restoration and revitalization of the Black Lagoon in a ceremony renaming Black Lagoon as Ellias Cove, in honor of the family who donated the adjacent land (Meyer-Ellias Park) to the City of Trenton.

A.9.7 References

USEPA Black Lagoon Legacy Act Cleanup Detroit River Area of Concern. http://www.epa.gov/glla/blklagoon/index.html.

Remediation of the Black Lagoon; Trenton, Michigan; Great Lakes Legacy Program. http://www.epa.gov/glla/blklagoon/BlkLagoonRpt032009.pdf.

Publication Date: August 2014