Constellation Energy Secures Water Permit for Three Mile Island Restart

Constellation Energy has secured a pivotal regulatory approval for the restart of its Three Mile Island nuclear power plant in Dauphin County. The Pennsylvania Department of Environmental Protection issued a Section 401 Water Quality Certification, a mandatory prerequisite for resuming operations at the facility. This certification validates the plant's compliance with state water standards, specifically addressing the thermal and volumetric impacts of its cooling systems on the Susquehanna River.

The permit allows the facility to withdraw up to 73.2 million gallons of water per day during peak operational days. Of this total volume, the certification specifies a consumptive use limit of 21 million gallons per day. These figures are critical for the plant's closed-cycle cooling technology, which is designed to mitigate the risk of impingement and entrainment of aquatic species while managing the thermal load of the discharged water.

Thermal Discharge Limits Defined

The certification imposes a maximum discharge temperature of 110 degrees Fahrenheit for water returning to the river. This limit is strictly calibrated to protect the Susquehanna River's designated uses, which include supporting warm-water fishes and migratory species. By capping the thermal output, the DEP ensures that the resumed operation does not exceed the biological tolerance thresholds for local aquatic ecosystems.

The regulatory framework relies on the continued use of closed-cycle cooling technologies to minimize ecological disruption. This approach reduces the direct interaction between the cooling process and the river environment, thereby limiting the impact on resident and migratory fish populations. The certification confirms that these operational methods meet the necessary water quality standards for the facility's restart.

Operational Constraints And Infrastructure

Beyond water management, the approval includes provisions for the ongoing maintenance of existing water obstructions and encroachments at the site. The facility must continue to operate, repair, and replace infrastructure such as bridges as necessary to maintain waterway integrity. These requirements ensure that physical structures do not exacerbate the environmental impacts associated with the plant's water withdrawal and discharge activities.

The permit is part of a broader regulatory oversight process for data center projects in Pennsylvania. Under the state's Data Center Executive Order, developers must secure all permits and local approvals before the DEP can review facility-specific permits. This sequence ensures that Constellation Energy meets all preliminary compliance requirements before the water quality certification becomes the final barrier to full operational status.

Regulatory Appeal And Compliance

Individuals aggrieved by the certification decision have a 30-day window to file an appeal with the Environmental Hearing Board. This period begins from the notice date of September 18, 2026. The certification serves as the definitive authorization for the plant to proceed with its water-related operations, contingent upon adherence to the specified withdrawal and discharge parameters.

Constellation Energy must now integrate these regulatory limits into its operational protocols for the restarted unit. The alignment of the plant's cooling systems with the DEP's standards is essential for maintaining its license to operate. Failure to adhere to the 73.2 million gallon withdrawal cap or the 110-degree Fahrenheit discharge limit could result in regulatory penalties and potential suspension of the water quality certification.