Sediment Sampling Program
Helps Identify Places to Dredge

Once EPA selected dredging for the Upper Hudson River in 2002, the next step was to determine where the PCBs in sediment were located and at what concentrations.

Under an agreement with EPA, GE undertook a comprehensive sediment sampling program, now completed, to provide information critical to the design of the dredging program. During the $20-million program -- the largest ever undertaken in the United States -- nearly 50,000 sediment samples were collected in the Upper Hudson. The results of the program were used to determine where dredging would occur.

Specifically, the program determined the distribution of PCBs in sediment, refined estimates for the quantity of PCBs in sediment and established the chemical and physical properties of the sediment to evaluate engineering options for sediment removal and processing.

Where to Dredge

In total, nearly 8,500 "cores," or columns of sediment several feet in depth, were collected in aluminum or plastic tubes. The cores were collected by manually pushing a tube into the sediment and vibrating the tube until significant resistance was encountered. Each core generated multiple samples.

The tubes were brought up from the bottom of the river, capped at both ends and transported to the GE plant in Fort Edward, N.Y. There, they each were sliced into approximately five sections (or samples), processed and labeled. They then were transported to independent laboratories approved by EPA and New York State for analysis of PCBs, other chemicals and engineering characteristics.

Crews conducting the sampling were carried on five boats equipped with global positioning systems (GPS). Other smaller boats were used to support the effort and to permit EPA and Army Corps of Engineers staff to supervise the work on the river.

In addition to the sediment sampling program, GE conducted side-scan sonar surveys to map sediment type and evaluate the presence, if any, of submerged archaeological artifacts. This technology uses sound waves to map the bottom of the river. Bathymetry investigations to determine water depths were conducted from Fort Edward to the Thompson Island Dam in 2005 and 2006.