Exide Group's long-awaited plan to get the lead out of Mill River faced a series of questions from Fairfield residents Thursday night at a state Department of Energy and Environmental Protection meeting in Fairfield Ludlowe High School.

Barry Mauri, of Bronson Road, even questioned whether Mill River would be deep enough for Exide's plan to dredge 21,400 cubic yards of lead-contaminated sediment along 4,000 linear feet of the river, from upper Southport Harbor to Mill Hollow Park.

"Has anyone looked recently at the tidal gate?" Mauri asked DEEP officials toward the end of the two-hour meeting. "I don't think it will hold enough water, except at high tide, for [a dredging operation]. Someone really has to look at the tidal gate. It's just leaking like crazy now, and it's ready to go."

"When that tide gate is out and it's low tide, all that sediment is exposed," Mauri said.

Stephen R. Kellogg, Exide's manager for the dredging project, said he also is concerned about the tide gates. "Every time I look at them, I cringe," he said. "We need water to do the project."

Thomas Steinke, director of Fairfield's Conservation Department, said the Mill Pond and Tide Mill gates are privately owned, and Tonia Selmeski, a DEEP environmental analyst, said if the state agency issued a permit for them, a condition of the permit would have been that they be maintained. "That's something we can certainly follow up with the property owner on," she said. "Obviously the work can't get done if there's no water."

Mauri also said a "huge tree" is in the river and wondered how a dredge operator could work around that.

Kellogg said Exide may have to do diver-assisted dredging. "We won't get too involved in removing trees. The trees we can work around. The bigger problem is the point you just made [about tide gates]."

Exide Group Inc. manufactured automobile batteries at its factory at 2190 Post Road from 1951 to 1981, and contaminated its 6.25-acre property and the adjacent Mill River with lead. In 2006, Exide demolished its factory and removed lead-contaminated soil and is now planning to clean the river.

Mill River is divided into five sections in Exide's remedial action plan. The highest concentration of lead in river sediment is 170,000 milligrams per kilogram near the site of the former factory, while the goal of the dredging would be to reduce that to no more than 200 milligrams per kilogram. In the other four sections, the goal is from 220 to 400 milligrams per kilogram, according to Traci Iott, a supervising environmental analyst at DEEP.

"We believe the cleanup discussed today will be protective of human health and the environment and will help restore the river to environmental goals," Iott said.

Kellogg said a hydraulic dredge would be used to vacuum sediment into large bags. Water then would be removed from the sediment, cleaned and returned to the river, while the sediment would be taken to one of three landfills, depending on how contaminated it was, Kellogg said.

He said using a hydraulic dredge instead of a cofferdam, in which parts of the river would be sectioned off and de-watered before sediment is removed, would create fewer odors. He said the dredge operator would use GPS to position the dredge and would be able to watch it underwater via a video camera.

Jane Cary of Stratfield Road and Kathryn Braun, a Fairfield lawyer and member of the Representative Town Meeting, were concerned about the river bottom after all the sediment is removed because Exide is not required to replace contaminated sediment with clean sediment. Exide plans to excavate sediment to a depth of one to three feet.

"I want to know what your plan is for filling in those holes," Cary said. "Exide is not responsible for restoring the topography of the river bed."

In response to Braun's similar concern about the river's "benthic substrate," Iott said, "When they take sediment out of the river, there will be substrate left in the river. There's a process where, naturally, these organisms will re-colonize the area."

Braun, though, wasn't satisfied. "If we end up with a dead river, is that their [Exide's] problem or our problem?" she asked.

Iott said, "We're authorizing activities that we believe will restore the river ... Information we have shows that will happen. If natural processes occur differently in this river than any other river, we'll address that at that time."

Braun also questioned whether Exide Group would still be liable to clean up the river if high concentrations of lead returned after the project is finished. Exide would confirm the dredging operation was successful in two phases -- after an area of the river has been cleaned so the dredging equipment can be moved, and then after the entire project is finished, according to Carolyn Fusaro, an environmental analyst at DEEP.

Robert Bell, assistant director of remediation at the DEEP, said Exide would be in compliance with DEEP's 2008 order to clean up the river after successful confirmation sampling at the end of the project. "If other issues are revealed in the future, the department has general authority to address those kinds of situations," he said.

Mill River's sediment is also polluted by chromium from Superior Plating Co. on the river's other bank, but Iott said that contamination is mostly in the same areas as Exide's lead contamination and would be removed in the dredging operation. She said the DEEP doesn't have data on chromium pollution in some areas of the river and that Superior Plating will have to go through an investigation similar to Exide's to see if additional dredging is needed to remove chromium. "There are a few areas they're not excavating because lead is not an issue, and they're responsible for lead," she said of Exide.

Fusaro said she understood concerns that the river should only be dredged once, and that DEEP is working with Superior Plating "to evaluate whether any additional sediment needs to be removed."

"That is our interest, to only have one disturbance to the river," Fusaro said.

Mary vonConta, chairwoman of the town's Harbor Management Commission, said her commission was concerned that dredging upstream in Mill River may cause pollution downstream in Southport Harbor. She said the commission also was concerned about the re-suspension of lead and chromium during dredging, the potential for shellfish and fish to be permanently harmed, and whether the bottom of the river would restore itself.

If the DEEP approves Exide's remedial action plan in late March, a contractor could be selected for the job by June 1 and equipment could be brought to the site by July 1, Kellogg said. The dredging would take place over two seasons, from August 2013 to November 2014, and confirmation sampling of sediment left in the river could be done in the spring of 2015, Kellogg said.

"We see this as about a season and-a-half dredging project. We'd like to do the half-season this year so we can do the full season next year," Kellogg said. "From the time it's a go from the DEEP, it's about a two-year evolution."

Regarding concerns about noise and odors, Ralph Klass, an Exide consultant, said Exide would follow Fairfield's noise ordinance and that dredging likely would take place between 9 a.m. and 6 or 7 p.m. He said odors would be minimized because the sediment would be sucked from the river into bags. Foaming agents could be used to mask odors if they arise when bags are opened, Klass said.

The remedial action plan requires approval from DEEP, and the project also requires permits from DEEP's Office of Long Island Sound Programs, the U.S. Army Corps of Engineers and the federal Environmental Protection Agency (for the discharge of contaminated sediment). Braun questioned whether the town's Conservation Commission also has to approve the project, but a definitive answer to that question wasn't given Thursday night.

DEEP is accepting public comments on Exide's remedial action plan until Feb. 11. Comments can be sent via e-mail to Fusaro at carolyn.fusaro@ct.gov