Update On Grasse River Superfund Site Restoration

The Alcoa Massena-West Plant is an aluminum production plant on the north shore of the lower Grasse River. In the 1950s, Alcoa began using and discharging polychlorinated biphenyls (PCBs) into the Grasse River, contaminating water and sediment.

A U.S. Environmental Protection Administration-led clean-up of this Grasse River Superfund Site began in 2019, and includes dredging and back-filling approximately four miles of shallow water habitat and capping approximately 6.5 miles of deep-water habitat with clean material.

In December 2019, NYS Department of Environmental Conservation (DEC) and the Saint Regis Mohawk Tribe signed a cooperative agreement to accelerate the restoration of natural resources in the St. Lawrence River Area of Concern (AOC) at Massena/Akwesasne, which includes the Grasse River.

As cleanup efforts began along the river, approximately 80 percent of the freshwater mussel community was determined to be at risk of destruction due to their inability to escape the work sites and the organism’s slow reproductive rate.

The Grasse River’s freshwater mussel community is remarkable for its density and diversity; at least 15 different species have been found here. The mussels perform the critical functions of nutrient cycling, sediment structure, and forage base.

The following actions have been completed, according to DEC:

• Moving nearly 500,000 freshwater mussels that would have been killed during the Grasse River cleanup. The relocated mussels are expected to help the remaining mussels recover and nearly doubled the population expected to survive;
• As required by DEC, Arconic installed 400 innovative “crib” structures to provide habitat diversity for fish until their natural habitat returns. The fish crib structures are made with cleaned, leftover construction materials, reducing the need for new materials;
• Improving the three largest freshwater wetland areas along the river by placing high quality soils, stabilizing areas of erosion, and planting native species. These efforts to restore the wetland will provide habitat for waterfowl, reptiles, and amphibians along the river; and
• Areas of upgraded habitat material are now providing a greater diversity of habitat for recovery of benthic invertebrates, an important food source for fish.

DEC is expected to continue to oversee these projects to ensure the habitat recovers as expected and expects to oversee an effort to return the recovered mussels to remediated areas, possibly as early as 2022.

For more information about the Grasse River Superfund Site, visit the U.S. EPA website.

Photo of freshwater mussels courtesy DEC.