A barge loaded with capping materials arrives at the in-water remediation site in 2019 on the Grasse River in Massena. (Provided photo — Christopher Lenney, Watertown Daily Times)

MASSENA — Environmental remediation work spanning decades is continuing this month on the Grasse River in Massena.

The U.S. Environmental Protection Agency on Tuesday announced the in-river work at the Alcoa Aggregation Superfund Site will resume in April. The site is a collection of properties owned and maintained by the former Aluminum Company of America, Alcoa, which changed its name to Arconic in 2016, and split into Howmet Aerospace Inc. and a subsidiary, Arconic Corporation, last year.

Howmet Aerospace is now responsible for implementing several plans developed by the EPA, state Department of Environmental Conservation and St. Regis Mohawk Tribe to address the legacy of industrial contaminants in the area.

The site includes a 7.2-mile stretch of the Grasse River — from the Massena Power Canal near Alcoa Road northeast to where the Grasse meets the St. Lawrence River. This year’s river cleanup efforts are a continuation of a 2013 EPA plan that called for dredging and capping of contaminated sediment. The plan, which was updated last year, involves dredging roughly 190,000 cubic yards of sediment contaminated by polychlorinated biphenyls, or PCBs. With no taste or smell and highly toxic when uncontained, PCBs were banned from commercial use in 1979.

Capping of the lower five miles of the total 7.2-mile stretch — from the Route 131 bridge to the river’s mouth — are the focus for 2021. A 12-inch sand, gravel and stone cap is planned for the five-mile section, and armored caps have been set in other sections of the channel. Last year’s dredging near Snug Harbor is expected to be backfilled with sand, and habitat reconstruction is lined up throughout the site. Dredged sediment, according to the EPA plan, is disposed at an on-site landfill permitted for the cleanup.

On shore, two staging areas will support this year’s 24-hour, 6-day-a-week operation. The existing staging area near the intersection of County Route 42 and Route 131 is being supplemented by a new area on Haverstock Road. Residents and travelers may note increased truck traffic around the staging areas.

Material is transported by either barge or a submerged pipeline along the shoreline, marked by orange and white buoys, and designated water crossing areas will be marked by green and red buoys. Boater safety information, as well as results from monitoring water, air, noise and light quality in the work zones, is viewable on the project’s website, thegrasseriver.com.

Alcoa’s presence in the town of Massena dates back to 1903, and for decades, the company released hazardous materials onto its properties and into the Grasse River through four industrial outfalls. When the EPA stepped in at the end of September 1989 to investigate the contamination’s extent, an arduous organizing and cleanup process began.

Informally called the Superfund program, the Comprehensive Environmental Response, Compensation and Liability Act was passed by Congress in 1980. The legislation created a fund for emergency cleanups and established a framework for the EPA and state environmental agencies to evaluate and remediate contaminated properties, mostly manufacturing plants, mining operations, landfills and other industrial facilities.

Of the more than 600 active Superfund cleanup sites in New York, including priority locations and those needing basic removal of materials, full assessments or corrective actions, five sites in Jefferson County, two in Lewis and nine in St. Lawrence are listed by the EPA.