East Lyme — The coalition working to prevent development of 236 acres adjacent to the Oswegatchie Hills Nature Preserve sought to build support for its efforts as its long battle with the would-be developer continues.

The coalition, formed in January of the Connecticut Fund for the Environment-Save the Sound and two local groups — the Friends of the Oswegatchie Hills Nature Preserve and Save the River-Save the Hills — gathered local officials and supporters at the public library Thursday to give an update on its legal case against the developer, Glenn Russo of Landmark Development, and lay out the environmental, public health and safety arguments.

Sign-up sheets at the entrance were collecting names of new members to join their cause, and a display with maps and photographs of the wildlife in the preserve will hang in the hallways outside the library until the end of the month.

Russo did not attend the event, and could not be reached for comment Thursday.

“Are we simply NIMBY folks, or are there significant environmental, public health and safety considerations that make this a bad plan?” Michael Dunn, co-founder of the friends group and its current director of land acquisition, asked attendees.

The coalition is seeking to add the 236 acres to the existing 457-acre preserve.

A civil engineer working for the coalition and other experts, Dunn said, have uncovered serious problems with Russo’s plan to build 840 housing units on 36 acres of the property.

Because of the shallow soils and steep bedrock terrain, the development would create serious runoff problems that would pollute the Niantic River and degrade wetlands on the property, he said.

In addition, plans for a single road in and out of the development would pose traffic and public safety problems, he said.

He cited a May 20 letter from Brian Thompson, director of the state Department of Energy and Environmental Protection’s Office of Long Island Sound Programs, which recommended the town Zoning Commission deny the zone change and preliminary site plan approval that Russo seeks.

The zone change and site plan are contrary to the standards of the state’s Coastal Management Act, Thompson said, and would severely impact water quality in the Niantic River and cause “significant environmental consequences.”

Thompson called the application “flawed and premature,” citing severe constraints on the ability to connect to town sewers or to create a community septic system there.

Also weighing in on the coalition’s efforts was DEEP Commissioner Rob Klee.

During remarks to the 40 people gathered at the library, Klee did not pledge state resources toward the purchase of the property, but offered his agency’s moral support.

Oswegatchie Hills, he said, is a “strategic” parcel that should be preserved to protect coastal resources.

He urged the group to take inspiration from the success of a similar coalition that obtained the 1,000-acre preserve coastal forest in Old Saybrook, Essex and Westbrook after a protracted battle with another developer.

“Keep up the good work,” said Klee. “It’s appreciated.”

Dunn said the developer is pursuing a “dual path” — seeking town approvals for the project and seeking to overturn previous denials in court, even as he negotiates with town officials on a possible land swap to trade the Oswegatchie Hills land for another parcel in town that could be developed.

“These are not easy conversations, but they are active,” Dunn said.

Roger Reynolds, director of legal affairs for Save the Sound, said he is confident the town and the coalition can make a “strong case” against the developer in Russo's appeal of the town’s denial of his request for 118,000 gallons per day of sewage capacity.

The town instead approved 14,000 gallons per day.

“I’m confident the town’s decision was well-based and rational,” Reynolds said. “The locals know this area, and they’re hitting back hard.”

Oral arguments in the appeal of the sewer decision are scheduled to be presented in Superior Court on June 20, Reynolds said.

j.benson@theday.com