Significant Project Features
- Excavation of ~75,000 CY of soil contaminated VOCs, PCBs, and hazardous levels of arsenic. Excavation depths ranged from 12-ft to 18-ft BGS
- Installation and extraction of 10 cantilever sheet pile cells (3,710 LF x 40 ft BGS maximum) to support excavation sidewalls and prevent groundwater infiltration
- Installation and operation of a well point systems in each cell to depressurize the aquifer and enable dry excavation
- Characterization, management, loading, and T&D of excavated material to multiple designated offsite disposal facilities
- Installation of ~ 90,000 SF of geosynthetic clay liner covered with cushioning soil overtop aquifer to replace natural meadow mat complex
- Backfill site with ~8,500 CY of stockpiled material approved for reuse and 60,000 CY of imported certified clean fill
- Installation of a 2-ft cap over the site after backfilling. Site restoration included replacing sidewalks disturbed by work operations and installing a perimeter fence
- Sevenson achieved 60,000 safe workhours without a lost-time incident
- Sevenson reduced the overall project schedule by several months saving over $600,000 in construction related costs in addition to engineering and project oversight costs
- Sevenson continually reviewed T&D pricing for all waste streams resulting in over $1.1M in cost savings
History & Location Details
Located in Camden, New Jersey, the Martin Aaron Superfund Site encompasses a large property used for over 30 years as a drum reconditioning facility. After operations ceased in 1998, arsenic, PCBs, VOCs, and other chemicals were detected as contaminants in site soils and groundwater. Steps were taken to mitigate the immediate impacts to human and environmental health through a series of interim remedial measures. This project, Phase I, OU-I, was awarded to Sevenson on a competitive bid basis.
Phase 1, OU-1 remedial action was designed to excavate, characterize, T+D contaminated soils; restore disturbed areas; and install a GCL cap. Upon receipt of the notice to proceed Sevenson initiated equipment mobilization and site set up. This included an ABI variable movement hammer and excavator mounted Robo-vibe; excavators; off-road haulers; a dozer; roller; front end loaders; rock crusher; as well as additional support pieces.
Sevenson installed a total of 3,710 LF of steel sheet pile as cells to reduce dewatering volumes; stabilize excavation sidewalls; eliminate the need for side slopes; minimize the impact of the excavation to adjacent structures; and provide a safe and stable work area.
Sevenson installed a trench along drivelines 7-ft BGS to clear drivelines of obstructions. The inboard side of the trench was backfilled with material excavated from the trench. 2-ft of freeboard was left exposed along the inside face of the sheet pile to facilitate installation of the well point manifold, utilized for excavation dewatering.
Sheet pile was installed sequentially, interlocking every sheet until the cell was fully enclosed. Sheet piling corners were made “tight” at all angle points using stock or fabricated corner sections with compatible interlocks. This ensured cells were virtually water tight.
Sevenson managed any surface water runoff with diversion dams. Surface water that accumulated around the sheet pile wall was pumped to the water treatment plant.
Waste excavation required segregation of arsenic contaminated material from other source material. This was identifiable as the soils were white in color. When encountered, arsenic soil was loaded into off road haulers and transferred to a secure area for analytical testing and final disposal.
Two excavators were used to load off-road trucks and transfer all soils to the stockpile area, when direct loading was not possible. The primary excavator was a long-front excavator capable of reaching out over 55-ft. and performed the initial waste removal. When possible, excavators loaded directly into road-certified trucks for offsite disposal at the approved landfill. After the excavation depths were achieved, an excavator was repositioned inside the excavation cells as needed to remove any remaining soil.
Utilizing an excavator, small dozer, and roller, Sevenson commenced backfill operations using material approved for onsite reuse or certified clean fill. A GCL cap was installed by lifting rolls into place with the excavator from outside the cell. Personnel inside the excavation rolled out the GCL with excavator assistance when necessary. The excavator placed and compact cushion soil overtop the GCL. A roller was used to meet compaction requirements of material and backfill.
Sevenson installed, operated and maintained shallow water dewatering pumps and well point systems for each sheeted cell. The shallow water included groundwater, precipitation, and decontamination water. The well points depressurized the underlying aquifer facilitating “dry” excavations below the potentiometric level. 10 systems were installed and removed. Well points were spaced to enable dewatering rates up to 300 gpm meeting the capabilities of the onsite water treatment system. Sevenson maintained constant communication between the WTP operator and excavation to balance the needs and capabilities of the two operations.
Upon completion of all excavation and backfill activities, Sevenson removed all sheet pile and transported it to the decontamination pad for cleaning. Interior sheet piles remained in place until all of the contaminated materials on either side of the pile had been removed.
A 24-inch soil cap was installed overtop the entire site, then graded and seeded. New sidewalks, curbs, and a perimeter security fence were installed to complete the project.