The Resuspension Standard

EPA established two resuspension standards to ensure that dredging did not cause exceedances of the drinking water standard and did not release more PCBs into the river than would have happened over time without dredging.

The first standard requires that during dredging the concentration of PCBs in the water not exceed the federal drinking water standard of 500 parts per trillion. (The PCB level in the water before dredging averaged 30 to 50 parts per trillion.) The second standard requires that the total mass of PCBs resuspended during dredging not exceed 117 kilograms (258 pounds).

Because of the volume of PCBs being dredged and the velocity of the river, and despite the fact that more than 55 percent of the volume of sediment dredged was subject to flow control/diversion during dredging, both standards were exceeded during Phase 1.

• The federal drinking water standard was exceeded 10 times.
• Dredging released 200 kg (440 pounds) of PCBs, as measured at Waterford 30 miles downstream, in exceedance of EPA’s maximum allowable limit.

Dredging released 3% to 4% of the PCBs dredged, consistent with the level of resuspension seen at other dredging projects, such as the Grasse and Fox rivers.

Resuspension also had another unforeseen impact not accounted for in EPA’s performance standards. It released PCBs to surface sediments downstream. This resulted in higher post-dredging levels of PCBs in surface sediments that are bioavailable to fish.

The level of resuspension led to significant increases in PCB levels in Upper Hudson fish. PCBs in yearling pumpkinseed and forage fish in the Thompson Island Pool increased by nearly 500%. At Albany and Troy, nearly 40 miles downstream of dredging activities, PCB levels in the two species rose 40% to 65% percent.

The resuspension problem was not eliminated by resuspension controls, such as a bank-to-bank flow control structure installed at the head of the eastern channel of Rogers Island where substantial dredging took place and a sheet-piled enclosure near Griffin Island. In fact, the higher-than-predicted resuspension occurred even with more than 55 percent of the volume of sediment dredged subject to flow control. Sheet piling reduced but did not stop PCBs from moving into the river and created a pool of water with elevated levels of PCBs, leading to elevated PCB levels in air nearby that often exceeded EPA’s performance standard for air quality.

Despite the Phase 1 experience, EPA is considering requiring significantly more sediment removal in Phase 2 — requiring a rate of removal double what was achieved on the best days of Phase 1. This would lead to the release of 2,000 kg (4,400 pounds) of PCBs downstream over the life of the dredging project. This also would mean that the drinking water standard of 500 parts per trillion would be routinely exceeded during Phase 2. This directly contradicts EPA’s own goals for the remedy and eliminates the benefits of dredging forecast by EPA.

To better control resuspension during Phase 2, EPA has recommended silt curtains with an adsorbent material and anchors. Silt curtains with an adsorbent material are being tested now; they have never been used in a full-scale project. The silt curtains used during the first phase of dredging were within two feet of the river bottom and anchored in a manner EPA approved. Dredging experience on the Grasse River and elsewhere shows that additional anchoring causes the silt curtains to tear when river flows and velocity rise, causing more resuspension and likely delays in the project.

GE has evaluated other ways to reduce resuspension, including dredging more slowly and avoiding dredging under high velocity conditions. Dredging more slowly does not reduce the mass of PCBs released downstream but it does increase the length of time needed to dredge and the duration of elevated levels of PCBs in fish. Avoiding dredging at times of high flow is not practical in the main channel of the Upper Hudson where much of the dredging will take place and will delay the project. The use of flow controls did not eliminate resuspension during Phase 1 and is not likely to do so in Phase 2. Moreover, many Phase 2 dredging areas are not suitable for structural controls.

To achieve EPA's long-term goals of reducing PCB levels in fish, water, sediment and downstream, while minimizing PCB level increases due to resuspension, GE recommends identifying the "tipping point" where dredging begins to release PCBs in quantities that undermine EPA's remedy. This "tipping point" should be used as the basis for a not-to-exceed cap on the mass of PCBs EPA will allow to flow downstream during dredging. Then, dredge areas can be prioritized to remove the maximum mass of PCBs available to fish without exceeding the established cap. GE also recommends keeping the federal drinking water standard as a performance standard, eliminating unproductive dredging to improve project efficiency, and maintaining EPA’s five-year schedule for the second phase of the project.