MASSENA — Dredging and capping work on the Grasse River Superfund site has been completed.

The site, also known as the Alcoa Aggregation, was an extensive project that began in 2019 and led to the removal of nearly a quarter million cubic yards of sediment contaminated with polychlorinated biphenyls (PCBs).

Over 200 acres of river bottom was capped, primarily with sand and powdered carbon, which works to capture and chemically bind pollutants in place, officials say.

Additional dredging of contaminated sediment was added to the project in 2020 in the Snug Harbor area, which is a small embayment located on the north shore of the river, according to officials.

The additional work was done to accommodate a new, larger tugboat purchased by the St. Lawrence Seaway Development Corp., which operates its tugboat out of Snug Harbor.

“This is an important milestone at the Grasse River Superfund site,” said Acting Regional Administrator Walter Mugdan.

“We have removed forever about 220,000 cubic yards of PCB-contaminated sediment, which will allow for the recovery of this vital and culturally important river system. This success could not have been achieved without the work of our partners, the Saint Regis Mohawk Tribe and New York State.”

Work will continue in 2022 to reconstruct habitat areas that were impacted by the project, officials say.

The project will require long-term monitoring, with a plan in place that requires fish, water and habitat monitoring to track recovery.

Fish consumption advisories previously established by the NY Department of Health will remain intact until PCB concentrations in fish are reduced to a point where the advisories can be relaxed or lifted by the state.

Capped areas of the river bed will be monitored to ensure the caps stay in place over time.

Arconic is conducting the cleanup, associated monitoring and habitat restoration under a 1989 administrative order with EPA.

This fall, EPA also initiated a five-year review of the cleanup that has been conducted so far at the site.

The purpose of this review, which is legally required under the Superfund law within five years after the start of on-site construction, is to ensure that the cleanup is working as intended and is protective of public health and the environment.

In conducting the review, EPA is reviewing Superfund site operation, maintenance and monitoring information.