Plans by Exide Group Inc. to dredge more than 20,000 cubic yards of lead-contaminated sediment from the Mill River is scheduled to begin Aug. 4.

But activity on Exide's 6.25-acre property at 2190 Post Road should start any day now.

Before dredging can begin, a wastewater-treatment facility has to be built and that work is scheduled to start before May 15, according to a project schedule provided by Carolyn Fusaro, an environmental analyst with the state Department of Energy and Environmental Protection. The schedule was from Stacy McAnulty, the project director at TRC Environmental Corporation in Madison, Wisc., the contractor working for Exide.

"They're going to spend the next couple of months building a processing plant," said Kathryn Braun, a lawyer for a neighborhood group known as Fairfielders Protecting Land and Neighborhoods. The wastewater-treatment equipment will separate water from dredged sediment and then cleanse the water before it's returned to the river.

First Selectman Michael Tetreau said the wastewater equipment, which will have long tubes, "will be very visible from the Post Road and will be on the site of the former Exide factory."

The Exide factory, which was demolished in 2005, was the site of battery manufacturing that caused the lead contamination in the Mill River. State and local environmental officials have made several attempts over more than three decades to completely clear the toxins from the river near the factory site.

Ken Money, Exide's representative and the project manager for the company, said Tuesday that Exide hadn't selected a dredging contractor yet, but that TRC Environmental Corp. is "very close to making their recommendation on who should do that work."

"The dredging activity will be managed by a very reputable company ... a very responsible company," Money said. He declined to identify an estimated cost for the project, which will be financed by Exide.

Money said Exide is "working diligently" to get the dredging project done.

"We promised a number of people we will get it done. There are lots of moving parts to this project and we have to be very careful as we move through each of those parts," he said.

The latest cleanup, which Exide is under an order from DEEP to do, divides 4,000 linear feet of the Mill River into five sections and is projected to last until November 2015, according to Conservation Department documents and the project schedule. The first section to be dredged is the farthest upstream, south of Sturges Bridge and north of Interstate 95, Braun said. The remaining four sections continue in order downstream until the final section on the Long Island Sound side of Harbor Road.

The cleanup standard for parts of the river that are below I-95 is a lead concentration of 220 milligrams per kilogram, while the standard above I-95 is 400 mg/kg, according to documents in the town's Conservation Department. The lower standard is to protect ecological health while the higher standard is for human health, according to the Conservation Department.

Tetreau said construction of the wastewater treatment facility and dredging would take place Monday through Saturday for about eight hours a day, but the dredging won't go on year-round because of "black-out" periods in spawning seasons. Those black-out periods affect two sections of the river and run from spring to fall, according to the project schedule.

Braun said it is "pretty exciting" that the dredging project would soon begin, adding that the dredging schedule was "very ambitious."

"It's expected to be done 18 months from when they start," she said. "Hopefully they don't find anything in there that makes the job last longer than that."

Braun said she hopes town officials post progress reports on the dredging project on the town's website, and Tetreau said that is likely. "Certainly anything significant will get posted on the town website, as well as would be distributed to each of the three commissions," he said, referring to the Shellfish, Harbor Management and Conservation commissions. He said those boards also would likely discuss the progress of the dredging project at their public meetings and that FairPLAN is on the distribution list for reports.

Tetreau said he also looks forward to the now-vacant Exide property generating more tax revenue once a mixed-use development is built on it following the cleanup. He said the property, which is just west of downtown, is the second-largest vacant commercial property in town (the Metro Center site on lower Black Rock Turnpike is the largest).

"We've got developers ready to go on that," Tetreau said of the Exide site. "It's been kind of a blot on the Post Road for as long as I can remember, since Exide shut down."

"It will be so much nicer to have a building there that fits and is representative of downtown Fairfield," Tetreau said. He said the town has "streetscape projects" under way along the Post Road past the Exide property, stretching from its intersection with Carter Henry Drive to its intersection with Sasco Hill Road that include sidewalks and landscaping.

Exide closed its battery plant in 1981, and its vacant factory stood on the site for about 25 years until it was demolished and lead-contaminated soil was removed. The land cleanup was done to residential standards.

"It's taken a lot of years and a lot of work by a lot of people to get to this point," Tetreau said, adding that Mill River is "one of the iconic features of our town and important to all of us."

"Our two guidelines are still the same -- we want the ... river cleaned up as soon as possible, but we want the river to be more live and higher quality once it's done than today," Tetreau said.

Exide isn't required to repopulate the bottom of the river with sediment or shellfish, but DEEP officials believe that process will happen naturally over time.