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Mirant Canal Station Final NPDES Permit

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Re-noticed for Public Comment: Entrainment-related Permit Conditions for the Mirant Canal Station Power Plant in Sandwich, MA

EPA Region 1 is withdrawing and re-noticing as draft permit conditions for public review and comment certain provisions of the final NPDES permit that the Region and MassDEP issued to Mirant Canal Station (Canal Station) on August 1, 2008 (August 2008 Final Permit). This action is being taken to address requests for additional opportunity to comment on these permit conditions.

Specifically, the Region is withdrawing and re-noticing as draft permit conditions for public comment those provisions of the August 2008 Final Permit that are based on Region 1's determination under section 316(b) of the Clean Water Act, 33 U.S.C. § 1326(b), that closed-cycle cooling is the best technology available for minimizing adverse environmental impact (BTA) with regard to reducing the entrainment of aquatic organisms by Canal Station's cooling water intake structures (CWISs). The provisions of the August 2008 Final Permit that are now being withdrawn and re-noticed as draft permit conditions are Parts I.A.2.f, I.A.7.f, I.A.8, I.A.13.g, and I.A.13.h. The new draft permit conditions are accompanied by a supporting Fact Sheet (December 2008 Fact Sheet), which incorporates the August 2008 RTC and provides background information and basis of these draft permit conditions.

The August 2008 Final Permit was appealed by the permittee (Mirant Canal) to EPA's Environmental Appeals Board (EAB) in Washington, DC, for review. This Final Permit has not yet gone into effect pending the resolution of the appeal. Therefore, the NPDES permit issued to Canal Station in 1989 remains in effect. In conjunction with the Region's decision to re-notice the above permit conditions, the Region has requested the EAB to stay the pending appeal until the new draft permit conditions are finalized.  Once the permit conditions are finalized, they may be appealed by any commenter. Any such appeals can then be consolidated with the existing appeal, so that all issues related to the permit may be heard by the EAB at one time.

The administrative record containing all documents relating to the new draft permit conditions, including additional items added to the administrative record since the issuance of the August 2008 Final Permit, is on file and may be inspected at the EPA Boston office mentioned above between 9:00 a.m. and 5:00 p.m., Monday through Friday, except holidays.

EPA accepted written public comments on the draft permit conditions from December 12, 2008 to January 29, 2009. After considering these comments, Region 1 will issue final permit conditions together with written responses to all significant comments. Once the draft permit conditions are finalized, EPA will address the appeal of the Final Permit and seek a resolution to all of the outstanding issues in order to have the Final Permit go into effect. A public hearing was held on January 14, 2009 at the Forestdale School in Sandwich, MA.

Public Comments

Mirant Canal Station power plant in Sandwich, MAView a larger version of this image.Background: EPA and the Massachusetts Department of Environmental Protection (MassDEP) have developed a Final National Pollutant Discharge Elimination System (NPDES) permit for the Mirant Canal Station (MCS, the Station) power plant in Sandwich, Massachusetts to meet the requirements of the Clean Water Act. MCS is a 1120 megawatt (MW) fossil fuel electrical generation facility that discharges pollutants, including heat, to, and withdraws cooling water from, the Cape Cod Canal (Canal). Steam turbine condenser waste heat is rejected to the Canal by means of a once-through cooling water system. Water for this cooling system is withdrawn from the Canal by the Station through two cooling water intake structures. Each operating day, the Station withdraws approximately 518 million gallons of water from the Cape Cod Canal and circulates it through the facility to condense the steam used to produce electricity. Water taken from the Cape Cod Canal by MCS contains millions of organisms including fish eggs and larvae. These organisms are pulled through (or "entrained") in the facility and killed by severe physical and chemical impacts and extreme water temperatures. Cooling water withdrawals also create a water velocity at the intake pipes which traps (or "impinges") many juvenile and mature fish against the intake screens causing injury or death.

EPA and the MassDEP last reissued the MCS federal and state permit number MA0004928 on June 23, 1989. This permit was scheduled to expire on June 23, 1994, but it has been administratively continued in effect pending reissuance of a new permit.

Major Permit Conditions: The major permit conditions to protect the water quality, aquatic life and designated uses of the Cape Cod Canal are as follows:

  • Construction of cooling towers or comparable technology: In order to reduce mortality to fish eggs and larvae that are entrained, MSC will be required to install cooling towers or alternative technologies and/or operational methods that may result in comparable reductions in entrainment mortality.

  • Improved Fish Return System: To reduce impingement mortality, the final permit requires that the cooling water intake structures are modified to include operational controls to reduce chlorine exposure, the use of fish holding buckets and low pressure spray washes, and the reconfiguration of the return system such that returned fish are transported away from the intake structures in order to reduce the probability of fish being re-impinged.

  • Discharge Temperature Limits: To ensure that the biological integrity of the receiving water is maintained, a thermal discharge limit was derived with two compliance points. There is a monitoring point in the discharge canal and also in the Cape Cod Canal. Compliance with the limits need to be achieved at both locations.

  • Internal Waste Streams: To ensure that dilution is not used as a means of compliance and in accordance with the federal regulations for the Steam Electric Power Generating point source category, metal cleaning waste water has been segregated from other internal waste streams for sampling.

  • Monitoring: To gather more information about the entrainment and impingement impacts from MCS and to gauge the effectiveness of protective measures, an extensive bio-monitoring program is required.

Public Comment: EPA accepted written public comments on the Draft Permit from December 22, 2005 to February 4, 2006. Federal regulations require EPA to respond to formal comments in writing. Summaries of these comments and EPA's responses to comments have been complied into a document listed below: "Responses to Comments for Mirant Canal Station."

Sharon DeMeo (
5 Post Office Square, Suite 100 (OEP06-1)
Boston, MA 02109-3912
Fax: (617) 918-1505

Mirant Canal Station (MCS) Final Permit Documents: