Formatted Title:

A Hybrid Remedy Implementation Case Study For Marsh Restoration In Brunswick Estuary, Georgia, USA

Background/Objectives:

The LCP Chemicals Superfund Site (Site) is in Glynn County, Georgia, immediately northwest of the City of Brunswick. The Site consists of a mix of tidal creeks, marshes, and brackish estuary and an adjacent upland area. Investigations of the marsh identified sediment and surface water contamination related to historical industrial operations at the Site. Site contaminants of concern include mercury, Aroclor 1268, lead, and polycyclic aromatic hydrocarbons (PAHs). The U.S. Environmental Protection Agency and Georgia Department of Natural Resources Environmental Protection Division Record of Decision for the marsh consists of multiple remediation technologies, including dredging and backfilling within the tidal creek system and thin layer cover (TLC) in designated areas in the marsh. Remedy implementation was completed in 2023, and initial long-term monitoring is scheduled for fall 2024.

Approach/Activities:

Full-scale remediation within the marsh system at the Site was completed in 2023, incorporating nearly 11 acres of marsh channel dredging of nearly 32,000 cubic yards (cy) of Toxic Substances Control Act (TSCA) and non-TSCA level sediment, backfilling 20,000 cy of sand, and TLC application over 11 acres of marsh. Removal activities incorporated floating equipment in the creek system, as well as mat-based access through the marsh to reach areas inaccessible by floating equipment. To mitigate turbidity during dredging operations and allow for additional operations using in-water equipment to minimize impact to the marsh, a temporary flow control structure was installed to stabilize water levels in the channel system and reduce impact of the >7-foot tidal swing on removal and backfill operations. Remediation from the landside was completed using an optimized mat road network allowing access to narrow channels inaccessible to floating equipment. Sediment removed from the channels was transported to the Site sediment processing area where material was stabilized for transport for final off‑site disposal. TLC application incorporated lessons learned from a previous pilot project to complete application of 6 to 9 inches of imported fill material over 11 acres of footprint. Following completion of dredging, backfill, and TLC, access roads within the marsh were removed and the portions of the marsh affected by the access roads were restored.

Results/Lessons Learned:

Applying lessons learned from previous pilot study activities, full-scale remedial activities were successfully completed in the complex marsh system with minimized marsh disturbance outside active remediation areas. Tide management by the flow control structure mitigated turbidity from dredging operations, allowed increased production rates from floating equipment, and reduced impact by reducing use of the mat road within the marsh system. TLC application successfully completed large-area placement by hydraulic rainbowing application of the cover material. This method provided targeted coverage with minimal disturbance to increase potential for marsh grass recovery on a faster timescale. Restoration efforts for the access roads within the marsh system are projected to increase plant recovery compared to the pilot study. Long-term monitoring will be initiated in fall 2024 and will provide preliminary results of the backfill and removal activities, with marsh grass recovery expected in 2 to 3 years.

Mike Marrone

Affiliation

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A Hybrid Remedy Implementation Case Study for Marsh Restoration in Brunswick Estuary, Georgia, USA