The Residual Standard

EPA established the Residual Standard — the amount of PCBs left on the surface sediments after dredging — to reduce the amount of PCBs that are or may become bioavailable. EPA’s target average for five-acre dredge areas was approximately 0.25 ppm, about one-quarter of a part per million. Sampling was required after each dredging pass to measure the mass of PCBs left behind.

The standard was not met in most areas dredged. In all but one area, despite multiple re-dredging attempts, the standard was met only with capping, i.e. putting down a clean layer of soil over parts of the area.

In addition, the testing, sampling and assessment of each of the dredging areas required more time than expected. Dredging was completed in 73 days. But, testing, sampling and assessment required an additional 35 days. This meant that each of the areas of the river that were dredged were open for at least three months. This hampered efforts to achieve the Productivity Standard.

In all but one of the five-acre areas dredged, 90 percent of the PCB mass targeted for removal was captured in the first two dredging passes. Nevertheless, achieving the Residual Standard still required further re-dredging attempts even when they removed minimal additional PCBs.

EPA has made a recommendation to correct the problem of unproductive re-dredging, but the recommended approach makes the problem worse. EPA would require that nine inches more sediment be routinely removed in each dredging area. GE’s analysis shows that this would result in removal, at a minimum, of an additional 400,000 cubic yards of clean sediment, requiring dredging at an even faster rate than achieved during Phase 1. EPA also proposes to require additional sampling and re-sampling in each dredge area, in an attempt to reduce the number of dredge passes. In reality, EPA’s recommendations will result in four dredge passes in most areas, which will further reduce productivity, and will require transportation and disposal of 400,000 cubic yards of additional material.

To remediate the majority of bioavailable PCBs in the most efficient manner while keeping dredge areas open for the least amount of time, GE recommends that the Residual Standard requirements for multiple re-dredging passes be modified as part of the Phase 2 design process after EPA establishes a not-to-exceed maximum limit for the mass of PCBs that dredging releases downstream.