Seven years after the EPA brought up the issue in a permitting process, two environmental groups say they will file suit to stop the Merrimack Station power plant from released too much warm water into the Merrimack River.
The plant takes water from the Merrimack and boils some to power turbines and some to cool machinery, then returns it to the river at a higher temperature. Back in 2011 the EPA suggested that the plant, then owned by Eversource under its previous name PSNH, should install cooling towers to reduce the amount of heat put into the river.
Since then nothing has been installed to mitigate the issue, although changes in the electricity markets mean that the plant in Bow is used far less often now than it was in 2011, so less warm water is returned to the river.
The Conservation Law Foundation and the Sierra Club said Friday they plan to sue Eversouce and Granite Shore Power, which bought the power plant earlier this year, to fix the problem.
Raising the temperature of rivers can harm existing wildlife and make it easier for invasive species to spread. The federal Clean Water Act defines heat as a pollutant, the groups noted.
