If the natural flow of PCB-contaminated groundwater from the Tecumseh plant reaches the Sheboygan River, it can eventually end up in fish tissue through the biomagnification process explained at the beginning of this report. PCBs ending up in fish tissue is the primary concern at the Sheboygan River and Harbor site. The U.S. EPA should specify what action it will take if PCB-contaminated groundwater threatens to pollute surface waters and endanger human health and the environment. No data on current contamination levels has been released. This action limit also permits action to restore groundwater quality contaminated by past releases of contaminants.
Natural attenuation relies on the breakdown of contaminants into less harmful components.
PCBs break down into less harmful components at an extremely slow rate. However, groundwater by its nature is not exposed to sunlight. The plan indicates that further investigation may show that natural attenuation is inappropriate to clean up groundwater at this site. However, the U.S. EPA has not indicated what level of PCBs will trigger any cleanup action beyond a mere monitoring program. To meet the official requirements as required by criterion 2 in the NCP, the plan must ensure that there will be a PCB concentration of less than 0.03 ppb.