Location: Manistique, Michigan
Dates: August 2016 - December 2016
Contract Value: $3,500,000
Role: Primary Contractor
This project consisted of mechanically dredging 10,000 cubic yards of PCB contaminated sediments and wood debris. Approximately 2,000 cy of the sediment was contaminated with TSCA level PCBs. All dredging was performed with White Lake’s Case CX460 Custom Long Reach Excavator equipped with real-time RTK GPS positioning system which allowed White Lake to adhere to an incredibly complex dredge matrix. Material encountered during the project ranged from soft silty sediment, sawdust/wood pulp, rock and gravel, and large slat wood debris.
White Lake removed approximately 1,600 tons of debris in the form of large wood slats from various dredge areas throughout the project. The dredging equipment employed by White Lake could manage this debris without issue and without slowing production. All debris was broken up into manageable sizes and disposed of with the dredge sediments at the appropriate landfill.
Following confirmation sampling of the dredge areas, White Lake installed a sand cap ranging from 1 ft – 2 ft across 90,000 square feet of the dredge area that failed confirmation sampling for residual PCB contaminates. Thickness control on the complex design surface was achieved through innovative use of the RTK-GPS dredge guidance coupled with hydrographic surveying and core thickness samples. Sand placement was achieved with an average over-placement of less than 1 inch.
All water generated during dredging, transloading operations, and weather events was captured and treated through a carbon filtration system and eventually discharged to the local waste-water treatment plant after confirmation sampling.
White Lake’s mechanical dredging methods were a key efficiency during this project because amount of water generated from dredging was very little. Water that was generated, was pumped directly out of the lined material barges and through the water filtration system. The entirety of the material unloading area and material dewatering/mixing pad were equipped with liners and sumps that would capture all water released by the material as well as all water from weather events.
Transportation & Disposal
All TSCA dredge spoils generated during this project were disposed of at a TSCA permitted landfill in Wayne Country, MI. All non-TSCA dredge spoils were disposed of at a local hazardous waste landfill. Due to the distance that TSCA materials had to be hauled, it was critical that spoils be de-watered and solidified adequately. Because of the nature of the material encountered during this project, stabilization was difficult but White Lake overcame this obstacle by adding additives to the spoils that allowed us to maintain adequate production.
Because of the high concentration of PCB contaminates, environmental controls implemented by White Lake were numerous. Some of the controls included: double lining of all material barges with PVC & geo-textile liners, turbidity curtains at the entrances to all dredging zones, utilization of a “moonpool” while excavating TSCA materials, LLDPE liners under all landside project areas (e.g. unloading dock), and custom environmental buckets on both the dredge and unloading machines.