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GE used PCBs, or polychlorinated biphenyls, as an insulating material in electrical equipment and discharged them into the river until they were banned in 1977. PCBs have been shown to cause liver cancer and other health problems.
Richard McGrath of the Isosceles Group, an environmental management and health services company, explained that a 2007 analysis of samples of the top six inches of previously contaminated sediment, where PCB contamination is most likely to resurface, showed that post-remediation PCB levels were at 0.17 parts per million.
Compared to the pre-remediation levels of 11 parts per million, the recent figure demonstrates a 99 percent decrease. The EPA also evaluated the migration of the contamination, using a model developed to calculate chemical levels, and found that 11 miles downstream from the GE plant, levels were decreased by 57.4 percent, and by 45.5 percent 19 miles downstream.
"That number is a reasonable estimation of what's going on out here," Mr. McGrath said of the Connecticut section of the Housatonic River.
Thus far, remediation efforts have been divided into three areas of the river, beginning at the GE plant-the upper half mile, the next one and a half miles and the rest of river.
GE completed work on the first segment between 1999 and 2002, incurring between $15 million and $20 million, while the EPA and the company tackled the second segment, or "reach," from 2002 to 2007, at a shared cost of $84 million. Approximately 110,000 yards of sediment has been removed.
"One of the fundamentals is knowing where you're going before you leave," said John Lortie, an environmental consultant with Stantec Consulting.
The EPA first identified its priority of human health and safety and pinpointed its goals of targeting erosion to the river bank and bottom sediment layers, decreasing downstream PCB migration, increasing the diversity and productivity of the plant and animal community and decreasing invasive species.
In the river adjacent to the GE plant, the agency examined the existing conditions, such as the channel depth, width and substrata, canopy density and bank stability, and considered limitations such as residential and commercial development right up to the edge of the river bank, a trapezoidal channel created by city redirection of the river's path in the 1930s. It also analyzed the administrative work involved in meshing the EPA remediation of the river and its bank with GE's remediation of the floodplain.
"One of our goals was not to go back to the property owners for maintenance," said Dean Tagliaferro, the EPA's project manager for the upper two miles of the Housatonic River's remediation, of the effort to leave a lasting solution to both the contamination and the ongoing erosion.
To that end, the agency planted 700 trees per acre and 700 shrubs per acre, used a native seed mix and geomembrane liners to ensure successful re-vegetation, and fortified the river bank with native marble and limestone rocks to combat erosion.
According to Mr. Tagliaferro, flooding will continue to be a problem, as the EPA was unable to raise the bank's height because of the potential impact to abutting property. Already in place is a five- to seven-year monitoring system, which calls for an 80 percent survival rate of the planted vegetation, no more than a 5 percent presence of invasive species and 95 percent of herbaceous cover, in addition to measures to observe erosion and PCB levels.
As for the rest of river, which includes the Connecticut portion of the Housatonic, a process of proposals for its remediation is ongoing. GE submitted a work plan on Sept. 1 that is currently available for public comment until Oct. 7.
The EPA will make the final proposal, which GE must design, construct and fund, to the public, taking into consideration GE's work plan and public response. Given the improvement in the fish population and the sediment samples that Mr. McGrath had cited, Susan Svirsky, project manager for this last section, indicated that active remediation similar to the efforts in Pittsfield are not likely to be the first choice.
"We have not come to any decision about what's going to happen downstream," she said.
According to Susan Peterson, an analyst for the Connecticut Department of Environmental Protection, the state and GE had a cooperative agreement in the 1980s to monitor PCB levels at local spots, such as Cornwall Bridge, Bulls Bridge and Lake Lillinonah. GE has since continued voluntary testing every two years, and the DEP is awaiting the most recent data. However, the priority remains the Pittsfield area.
"We're very concerned about controlling the source in Massachusetts," Ms. Peterson said.
