DOVER —On Sept. 13, three members of the Great Bay Municipal Coalition filed their notice of intent to sue the Environmental Protection Agency over nitrogen release changes being mandated for several Seacoast wastewater treatment plants.

The coalition, which includes the municipalities of Rochester, Portsmouth, Dover, Newmarket and Exeter, already filed suit against the state Department of Environmental Services in the spring.

The communities argue that DES did not follow the correct rulemaking procedures when implementing a new nitrogen water quality standard of 3 milligrams per liter in 2009.

In coming up with their nutrient criteria in 2009, DES determined there was a causal effect between nitrogen discharge from wastewater treatment plants and the dying of eelgrass, an important wildlife habitat and indicator of the estuary's health.

The EPA is using that criteria in the issuance of wastewater treatment plant permits.

Dean Peschel, spokesman for the coalition and an environmental consultant for the city of Dover, said between 2005-2008, eelgrass declined dramatically, and nitrogen levels did rise in the bay, but the coalition has research to suggest the two are not related.

“We hired other consultants to look at the information that the state had used to come up with this conclusion, and these guys were national experts, and they looked at it and said, 'This report is totally wrong,' so we began to try and engage both New Hampshire DES and the EPA,” Peschel said.

Three years into that effort, Peschel said they still have not been provided an opportunity for dialogue with DES and EPA.

Most recently, the coalition presented data that showed eelgrass has been coming back to the estuary since 2009, and nitrogen has been dropping to levels seen in the early 1990s, when eelgrass was doing fine, without any changes to area wastewater treatment plants. The coalition believes historic levels of rainfall between 2005 and 2008 may have played a role in the eelgrass die-off.

“So we think this is just new evidence that shows that reducing nitrogen dramatically at wastewater treatment plants at the requirement EPA is proposing is not the answer to the problem,” Peschel said.

Peschel said Dover's wastewater treatment plant discharges 22 milligrams of nitrogen per liter, and it has committed to knocking that number down to 8mg/L.

Portsmouth has proposed similar plans.

But the state and EPA are looking for the municipalities to reduce the nitrogen levels to 3 mg/L, which is the limit of technology. The coalition has said this requirement will cost them hundreds of millions of dollars with no guaranteed benefit.

“The difference between the cost of getting to three versus an eight for Dover, over the 20-year cost of doing that, would be on the order of $94 million,” Peschel said. “This may not even be the problem, so why are we pushing our communities and residents to spend this extraordinary amount of money, which is — from what our knowledge shows — not going to make a difference,” Peschel said.

Portsmouth's deputy director of public works, Peter Rice, said the municipalities have been pushed to lawsuits by a lack of willingness on the part of the EPA to review the science.

“We believe the data clearly points to other issues going on in the bay and an incremental, adaptive approach is much more appropriate in this situation,” Rice said.

He said it is easy for regulators to tell communities they have to do something, but it is going to “bankrupt” those communities.

Rochester Mayor T.J. Jean has said the requirement could more than double sewer rates in his city, making the job of attracting businesses more difficult.

gmacalaster@newstote.com