Waterford — The state Department of Energy and Environmental Protection has begun its review of technical details of the water intake and discharge permit application for the Millstone Power Station that could ultimately decide whether the plant will be required to build cooling towers.

The lengthy process will entail DEEP deciding how it will apply new federal rules for plants that use large amounts of cooling water.

DEEP informed Millstone owner Dominion Resources on March 6 that its application for a new permit has been accepted for review. The current permit, which expires Aug. 31, allows Millstone to draw in more than 2 billion gallons of water per day from Long Island Sound to absorb waste heat generated by its two nuclear reactors, and to release the heated water into the Sound. The DEEP notice informs Millstone that its current permit will remain in effect until the agency reaches a final decision on the renewal application.

DEEP spokesman Dennis Schain said Monday that Millstone is expected to submit additional information through early 2016 in response to state requirements and the new federal Environmental Protection Agency rules. In May, the EPA issued a long-awaited decision that gives states the authority to decide how nuclear power plants and other facilities that use large amounts of water for cooling should be required to minimize harm to fish and other marine life.

The decision avoided a specific mandate for cooling towers, large structures that recycle cooling water and eliminate the need for new daily withdrawals, which environmental groups have been pushing for.

Roger Reynolds, legal director for the Connecticut Fund for the Environment & Save the Sound, said Monday that his organization plans to press DEEP "to do an adequate study" and require "a closed cycle cooling tower that is going to be best for Long Island Sound." Cooling towers, whether large, 500-foot-tall structures or smaller, mechanical towers, would protect fish and other marinelife that now get trapped and die in Millstone's intake pipes, Reynolds said. They would also protect the Sound from regular inputs of warmed water that further raise the temperature of the estuary, already stressed by climate change, he said.

Ken Holt, spokesman for Millstone, said the plant is already using "the best available technology to limit impacts on the environment." The plant's intake pipes are fitted with 3/8-inch mesh screens that catch many fish and other creatures before they enter the plant. Also, the plant has installed equipment that reduces water use and further cuts back during winter flounder spawning season in April and May.

Dominion has estimated it would cost $2.6 billion to retrofit Millstone with cooling towers, and that energy output would be reduced as a result.

In addition to seeking permission to continue cooling water withdrawals and discharges, the new application also includes a request to change the location of some of the storm drains and other discharge equipment at the plant, Holt said.

It also seeks permission to use corrosion-inhibiting chemicals in the cooling water. The plant does not currently use these chemicals, but industry groups are recommending them to help maintain equipment, he said.

"If we do decide to use them, DEEP is aware of them and can provide guidance on what kind of monitoring will need to be done," he said.

Schain said once DEEP completes the technical review, staff will prepare a tentative decision on the application. At that time, a fact sheet and draft permit would be made available to the public, and a public hearing on the proposed decision would be scheduled.

j.benson@theday.com

Twitter: @BensonJudy