Hudson River Cleanup – Phase 2
Sediment Remediation Support Services
Following completion of Phase 1 of Hudson River PCBs Dredging Project in November 2009, the project was refined to tune the design, performance standards and construction implementation for the remainder of the 5-year program. Improving elevation of contamination (EoC) delineations, backfilling timing, sediment processing throughput, and coordination on river flows, were just a few examples of optimizations that would be needed based on conditions realized and experience gained during Phase 1 of the project.
Lally Consulting LLC continued to collaborate with the dredging contractor, Cashman Dredging & Marine Contracting LLC (Cashman) to provide sediment remediation expertise and quality control support through project completion for each of the remaining five (5) Phase 2 construction seasons (2011-2015). Lally’s work encompassed construction quality assurance and optimization assistance with the following activities;
- Inventory and Residual Dredging
- Backfilling / Capping
- Resuspension Control
- Hydrographic Survey
- Barge Transport
- Debris Removal
- Quality Control
- Vessel Traffic Control
- Calibration Control
- Other Operations
This work involved monthly embedment of Lally in project operations, extensive data analysis, graphics development and reporting.
Up to seventeen (17) next-generation precision excavator platforms with dredge and bucket positioning systems (DBPS) optimized and operated by Cashman were employed. Over 90 individual certification units (CUs) were remediated over the course of Phase 2 in varying, oftentimes challenging, river conditions. All dredged materials were placed in hopper barges for transport upriver to the Ft. Edward Sediment Processing Facility where it was transloaded, underwent course fraction separation, followed by mechanical dewatering of fines slurry to generally better than 60% solids by weight, before loadout into railcars for transport to regulated out-of-state landfills for Title D or TSCA disposal.
Project dredging was completed in October 2015, ultimately removing over 2.75 Million CY of contaminated sediment, and 310,000 pounds of PCBs, from the Upper Hudson River.
Installation of backfill and engineered caps was performed using converted precision excavator platforms and the SWATH method developed by Lally at earlier Superfund sites. Three types of backfill were placed depending on residual contamination level; One-foot backfill, Habitat backfill, and Nearshore backfill. Backfill placement supported one of the largest aquatic restoration planting efforts ever undertaken, with approximately 1.4 million submerged aquatic vegetation (SAV) or riverine fringing wetlands (RFW) plantings installed as part of the comprehensive plan approved by USEPA.
Several types of engineered caps were also installed to isolate and stabilize residual sediments. The caps incorporated varying gradations and thicknesses of granular or stone materials in order to resist erosion forces under different worst-case river conditions. The granular cap layers were also amended with total organic carbon (TOC) to further sequester residuals.
All project backfilling / capping work was completed in November 2015. In total, Cashman placed imported clean backfill and/or cap material to design thicknesses and grades over a designated 493 acres of the Upper Hudson River with outstanding accuracy and production rates.
In April 2019, following the Final Second Five Year Review, USEPA confirmed that the Hudson River PCBs Superfund Project is complete, and expressed the project has been a success. The project achieved a reduction in PCB levels in sediment of up to 96%, with over 99.8% of sediment in the Upper Hudson River showing PCB levels below EPA’s dredging criteria.
Given the complexity of the project, number of floating plant, site conditions, and large-scale logistics involved project execution by the Cashman’s project management and operations personnel was extraordinary.
Services Provided
Sediment Remediation Technical Support
Dredging and Capping Performance Optimization
Quality Assurance
Location
Ft. Edward – Schuylerville
New York, USA
Period
2010 – 2016