MASSENA Dredging the Grasse River is not the best method for cleaning it up, according to Alcoa officials a conclusion with which the St. Regis Mohawk tribal government disagrees.
The U.S. Environmental Protection Agency has proposed a $243 million remedial action plan for the river, a cost Alcoa will fund. The proposed plan requires dredging and capping of contaminated sediment in a 7.2-mile stretch of river.
For more than 20 years, Alcoa has worked with state and federal agencies to remediate contaminated areas near its Massena East and West plants, and cleaning up a several-mile stretch of the Grasse is the next step in that process. The EPA will finalize the proposal after gathering public comment on it through Nov. 15.
The plan recommends dredging approximately 109,000 cubic yards of contaminated sediment in areas close to the shore. In the rivers center, approximately 225 acres of sediment would be capped with clean sand and gravel to isolate the contamination. Another 59 acres would receive an additional armored cap of large rocks to further isolate that areas contamination.
Alcoa completed a pilot river dredging project in 2005 on approximately 24,000 cubic yards of sediment in the Grasses main channel, according to Larry J. McShea, project manager. The pilot project was part of the $65 million in cleanup research Alcoa spent on the river.
The pilot was unsuccessful, Mr. McShea told members of the Massena Remedial Advisory Committee at a meeting last week. The bottom layers of the river are difficult to dredge because they contain hard materials that equipment cannot successfully remove.
It makes it very difficult to get the sediment youre targeting out, he said. Its not a good river to try and dredge because of the site-specific conditions we have here.
Alcoa had to cap areas in the rivers main channel at the end of the pilot because it was unable to dredge them, Mr. McShea said.
It was a very difficult project. It was not a good outcome, he said. It was hard to see where we provided a lot of benefit.
But dredging a contaminated area still can be more beneficial than capping it, according to Jacob C. Terrance, Superfund oversight specialist with the St. Regis Mohawk Tribes Environment Division.
The tribal government is pushing for more dredging in the final cleanup plan than the EPA has proposed. Environment Division officials still are considering which option they would like the EPA to pursue.
Their preferred option could cost at least $350 million, more than $100 million more than the EPAs plan, Mr. Terrance said.
Ideally, wed like to see all the contamination removed, but thats not feasible, he said. The main channel is where we feel more dredging should be performed in order to make the remedy a more permanent remedy.
Dredging initially stirs up contaminants but can remove them in the long run, Mr. Terrance said. Polychlorinated biphenyl levels in smallmouth bass, brown bullhead and spottail shiner all spiked during the dredging, but subsided in the years afterward to near pre-dredging levels, he said.
To dredge it now will lead to adverse short term effects but be more protective of the future, Mr. Terrance wrote in an email.
But much of the post-dredging reduction in contamination levels was because Alcoa capped those areas, Mr. McShea countered. PCB levels are gradually falling naturally, he said.
Some in attendance at the RAC meeting expressed concern over what a severe ice jam could do to the protective cap. But Mr. McShea said the EPA plan includes monitoring the cap into the future to ensure there are no changes to it.