Manistique River AOC – OU1 & OU2

Project Summary

LOCATION: Manistique, Michigan
SCOPE(S) PERFORMED: Dredging, Capping, Sediment Management, Hydrographic Surveying

White Lake Dock & Dredge contracted with the Michigan Department of Environment, Great Lakes, and Energy to provide dredging and remedial capping services in the Manistique River AOC for both Operational Units (OUs) 1 and 2. Between both phases, more than 52,000 cubic yards of PCB impacted sediment were dredged, of which approximately 3,100 cubic yards were regulated TSCA. Material types varied considerably throughout the dredge areas; ranging from granular sands to fine-grained silty clays, to silty sands intermingled with significant quantities of slab wood and other debris.

The dredge templates consisted of extremely complex dredge-to surfaces designed to precision target removal of PCB impacted materials. This included the breaking of each DMU into sub-DMUs (with varying excavation depths) for purposes of confirmation core sampling, re-dredge, and capping. All materials were mechanically dredged utilizing a customized Volvo EC480 EL Long Reach excavator (equipped with RTK-GPS dredge guidance software and White Lake Dock & Dredge’s environmental dredge bucket). Despite the complex dredge to templates, dredging was performed within the allowable tolerance of -6” to +0” while generating less than 1.2% non-pay volume. Following completion of each dredge pass, confirmation core samples were obtained. Based upon the results of the confirmation cores, additional dredge passes were conducted within failed sub-DMUs up to a maximum of two times. Re-dredge typically consisted of a 6” lift with 6” over dredge tolerance. Areas that continued to fail were then capped. In total, we estimate that less than 10% of the sub-DMUs required re-dredge.

All materials were dewatered on site in the lined dewatering and solidification pits constructed by White Lake Dock & Dredge. For TSCA materials, sediment was solidified to meet landfill acceptance criteria with Portland Cement at a rate less than 5% by weight before trucking and disposal at a permitted disposal site in Roachdale, IN. Non-TSCA materials were solidified to meet landfill acceptance criteria with a combination of kiln-dried sawdust (a locally available product) or Portland Cement and disposed of at a local subtitle D landfill. When using sawdust, approximately 1.1% by weight was utilized. All water generated during dewatering operations was treated through an on-site pre-treatment system before being tested and then discharged to the local WWTP.

Following dredging operations, White Lake Dock & Dredge installed more than 15,000 CY of cap materials consisting of a combination of sand or sand amended with GAC over sub-DMUs that failed confirmation core sampling. Cap thickness generally ranged from 1’ to 2’ in thickness with a tolerance of -0” to +3”. When applicable, GAC was blended to a minimum of .5% by weight which White Lake Dock & Dredge achieved with a .02% overage.

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