WINDHAM — The federal government has added a former Windham mill to a nationwide list of hazardous sites considered high priority for clean-up.

The U.S. Environmental Protection Agency has added the Keddy Mill to the National Priorities List for its Superfund Program.

The mill once made paper and later steel flanges. The site contains an estimated 55,000 tons of material contaminated with polychlorinated biphenyls, or PCBs, which are suspected of causing cancer. The mill closed four decades ago.

The priority designation means the EPA will conduct an environmental review, determine who is responsible for the contamination, and attempt to get them to pay for the clean-up.