Last fall, Nelosca Technologies, Inc. (Nelosca) crews successfully concluded environmental remediation efforts after 3.5 years on the Grasse River in Massena, NY. This project had a challenging scope involving dredging, material processing, water treatment, mussel relocation, capping, and habitat restoration. Through a combination of strong teamwork and outstanding production efficiencies, our team completed every phase of work and executed a safe demobilization. Here’s how we did it.
Cap Pilot Test
In the first step in the Grasse Rive project, a small crew of Nelosca operators and office staff mobilized to the site in New York, to lay the groundwork for the project. The primary goal of our cap pilot test was to install settlement monitoring equipment on the riverbed, followed by placing the components of a multilayered armor cap that would allow our client’s engineers (namely Anchor QEA and CDM Smith), to assess how in-place cap material would settle on the river bottom.
Mobilization, Dredging, Processing, and Water Treatment Set-Up
During the first full year of work, Nelosca began full-scale remediation operations on the Grasse River starting with mobilizing most of the equipment and barges that we would use throughout the project. From March through November, 64 office staff and crew worked together on the project.
The overall goal in our first year was to dredge impacted areas along the north and south shorelines of the river to meet project criteria as agreed by the client and the Environmental Protection Agency (EPA). To facilitate dredging operations, we utilized 2 dredge plants. We placed dredged material into Nelosca’s custom-built hopper barges and transported it via pushboat back to our Route 131 Staging Area.
Our Grasse River team is shown transporting dredged material via pushboat.
At the staging area, we offloaded the material and processed it through a custom-built processing system. The processing system separated out larger boulders and other debris from the sediment and then dosed that sediment with Portland cement to help stabilize the material for off-site shipment.
Our subcontractor, Infrastructure Alternatives Inc. (IAI), set up a mobile water treatment plant to pretreat water that was either collected on the sediment processing pad or was pumped out of the dredge hopper barges.
Once dredged areas were approved, 2 backfill plants followed the dredging operation, placing clean material back into the dredged areas to meet pre-dredge elevations.
A separate group of pushboats moved loaded barges of backfill material from the Route 131 Staging Area to the 2 backfill plants. Nelosca also mobilized our custom long-reach amphibious excavator to the site to assist in dredging and backfilling nearshore areas and flood plains that could not be accessed with barge-based excavators.
Backfill placement operations on the Grasse River unutilized our amphibious excavator.
Dredging Snug Harbor, Backfilling, Capping, and Mussel Relocation
The COVID-19 pandemic forced Nelosca’s crew to delay mobilization to the site for the 2020 season while we worked to obtain essential worker authorization from New York state. During that time, Nelosca was awarded an extension to the original dredging contract, adding the removal of another 100,000 CY of dredge material from Snug Harbor, an area at the mouth of the river. Operations began back on the river in May, with approximately 73 office staff and crew.
Once on-site, dredging operations in Snug Harbor began using a process like our 2019 operations while a separate crew worked to reconfigure 2 backfill plants to create 2 Broadcast Capping System (BCS™) placement plants.
Nelosca's spreader St. Lawrence is one of our patented broadcast capping systems (BCS™).
Our capping goal on the Grasse River in 2020 was to place a 3-layer armored cap across a 54 AC area, composed of a chemical isolation layer (CIL), gravel filter layer (GFL), and armor layer (AL). With the BCS and a hydraulic slurry plant fully assembled, crews began placement of the CIL beginning at the uppermost extent of the project and working downstream covering approximately 54 AC of the main channel. Once we completed the CIL, a different plant was brought online to place the GFL; this plant was configured to mechanically feed the BCS using a material handler.
Material barges were loaded at the Route 131 Staging Area with GFL material and then transported to the placement plant with a pushboat. With the GFL complete, both BCS placement plants were again reconfigured to create 2 mechanical placement plants outfitted with 130,000 LB long-reach excavators. The mechanical placement plants, fed by material barges and pushboats, were used to place a final layer of armor stone across the entire 54 AC area.
On a downstream section of the river, Nelosca’s ADCI-certified dive team mobilized to the site to conduct nighttime mussel collection and relocation as part of the New York State Department of Environmental Conservation (DEC) mussel protection initiative.
At this point, dredging operations were completed for the original project. Crews ripped up the asphalt pad used for sediment processing operations and shipped it off-site. In late fall, we began constructing a second staging area in preparation for the 2021 season. We’d use the staging area as a second capping land plant to facilitate capping operations on the downstream section of the river during 2021 operations.
Final Cap and Habitat Restoration
After a pause over the winter, in-river operations resumed on the Grasse River in March 2021 with office staff and a crew of 57. Crews worked to configure our 2 BCS™ capping plants, fuse approximately 20,000 FT of pipeline, and assemble a second hydraulic slurry plant at the newly developed Haverstock Staging Area.
A photo of operations at the Haverstock land plant and staging area.
Prior to re-mobilizing in March, the client identified a small section at the mouth of the river that required further dredging to provide additional draft for larger vessels operating near Snug Harbor. Nelosca’s team assembled a small-scale sediment processing system at the Route 131 Staging Area. Utilizing a self-contained sediment processing and amendment system, mixing dredged material inside a concrete bin, we stabilized the 5,500 CY of material that was removed in the area.
The scope of capping operations in 2021 required placing a 2-layered cap across 195 AC, starting at the terminus of the armored cap placed in 2020, stretching to the mouth of the river. Operations began working around the clock 24 HR per day, 6 days per week, placing a CIL like that placed in 2020. Once the CIL was verified complete, the second layer of non-amended sand termed a "habitat layer" was placed.
Our team placed rootwad trees in the Grasse River as part of habitat restoration operations.
Upon completion of the habitat layer, crews transitioned to assembly and installation of several habitat restoration features including rock clusters, anchored rootwads, and fish cribs.
Throughout the final summer of operation, crews conducted several mechanical placement operations: backfilling certain areas dredged in Snug Harbor, placement of high organic content topsoil in flood plain areas, and covering over 3.5 AC of the river with a modified armor layer cap.
For details on Nelosca’s dredging, remediation, and habitat restoration capabilities, please visit our Environmental Services page and connect with our team.
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