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New Discharge Permit for Mirant Kendall Power Plant in Cambridge, Mass. Significantly Advances Protections for Charles River

Release Date: 09/27/2006
Contact Information: David Deegan, EPA Public Affairs, (617) 918-1017 Ed Coletta, Mass DEP Public Affairs, (617) 292-5737

(Boston, Mass. – Sept. 27, 2006) – A new water discharge permit for the Mirant Kendall Station power plant in Cambridge, Mass. will significantly increase protections for ecological health and recreational water uses of the lower Charles River and Boston Harbor.

The final permit, issued jointly by the EPA’s New England regional office and the Massachusetts Department of Environmental Protection (MassDEP), outlines wastewater requirements for the 256-megawatt, four unit Kendall Mirant power plant, which is the largest industrial discharger on the Charles River. The new permit addresses adverse impacts to sustainable fish populations due to heat and the intake of cooling water, and to protect aesthetics and recreation use. EPA and MassDEP worked to ensure that establishing these permit limits would be done while allowing the expanded power plant to remain an ongoing source of electric power for the greater Boston area.

“We are taking another major step towards the recovery of the lower Charles River and Boston Harbor,” said Robert W. Varney regional administrator of EPA’s New England Office. “The lower Charles River Basin is an active, valuable ecosystem which historically was home to abundant populations of migratory and fresh water fish. With this action, EPA and the Commonwealth are further advancing the ecological restoration of the River as sustainable fish habitat and ensuring the River will be a treasured recreational resource.”

The new permit includes appropriate regulatory conditions to ensure the power plant’s “once-through” cooling system, which requires water withdrawals from the Charles River and heated discharges back in to the river, meets federal and state water quality standards and protects fish populations and the aquatic habitat in the river.

“The high water temperature in the Charles River Basin has definitely had an impact on the habitat of fish in the river over the years,” MassDEP Commissioner Arleen O’Donnell said. “The new limits in this permit will help natural fish populations return to healthier levels. It will also significantly improve the overall water quality of the Lower Charles River Basin, where millions of dollars have been invested by the MWRA, local communities, and state and federal agencies to clean up this tremendous natural resource.”

EPA, MassDEP and many other state and local agencies have worked steadily for many years to improve ecological conditions in the lower Charles River, with a goal that the lower Charles should be fishable and swimmable. The new final permit is designed to help achieve that goal by protecting river herring and various other fish species that live and spawn in the river.

The Kendall station uses a once-through cooling system that is permitted to withdraw an average of 70 million gallons a day from the Charles River and discharge it back into the river at temperatures increased by 20 degrees Fahrenheit, or up to a maximum discharge temperature of 105 degrees Fahrenheit.

In developing the final permit conditions, EPA and MassDEP paid especially close attention to the facility’s potential thermal impacts to the river and its most sensitive fish populations – in particular, resident fish such as yellow perch and migrating fish such as alewife.

To address these ecological issues, this permit includes the following new protective requirements and conditions:

Zone of Passage and Habitat: A seasonal safe “Zone of Passage and Habitat”, which covers roughly 85 percent of the surface area of the lower Basin, has been created along the Boston side of the Charles River in order to protect fish populations and aquatic habitat. Two species of river herring, alewife and blueback herring, use the lower Charles River Basin for their annual adult migration and spawning run. The Charles River supports one of the largest river herring runs in Massachusetts Bay.

In-stream Temperatures: Maximum seasonal allowable in-stream river temperatures have been established within the Zone of Passage and Habitat. Critical river temperature permit limits range from 61 degrees Fahrenheit during early spring for yellow perch up to 81 and 83 degrees Fahrenheit during the summer for alewife. In addition, river temperatures in this safety zone cannot increase by more than 5 degrees Fahrenheit above upstream ambient river temperatures during a 24-hour average period. If real-time monitoring indicates that any of these temperature limits will be exceeded, the power plant must modify its operations to reduce thermal discharges to the river.

Barrier Net: A fine-mesh barrier net system or other similar technology must be installed in front of the facility’s cooling water intake structure to limit the number of fish and larvae that are trapped or pulled into the power plant when river cooling water is pumped into the facility.

Real-time Monitoring: Continuous water quality monitoring will be required in the lower River Basin. This monitoring will provide real-time temperature measurements at eight strategic upstream and downstream river locations. The real-time discharge monitoring information will be made available to EPA and MassDEP to ensure continued permit compliance and allow the power plant to take immediate action to protect the Charles River.

This permit will be in effect for a period of five years.

More information: Detailed information about the new final permit (

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