Along a riverfront that was once one of the nation's most important industrial centers, Chester has become an important center for something else - waste treatment plants.

When an incinerator and other facilities swept into the city in the 1990s, they were controversial, setting off suits, protests, and debates over health concerns and "environmental justice" in a Delaware County city where about one-third of the residents live in poverty.

While tensions have ebbed, a plan to build two new buildings at the incinerator complex and import trash from New York has stirred them anew.

The City Council, which will have final say, is expected to take up that proposal this week.

This time around however, the debate has taken on a different character.

One group of environmentalists is fighting against the proposal from Covanta.

But a group of local activists - Chester residents who were behind the original protests and lawsuits of the 1990s - is fine with the incinerator plan.

"Nobody wants them in their back yard," said Horace Strand, a local pastor and leader of the Chester Environmental Partnership.

Acknowledging that the facilities - which also include sewage treatment and manufacturers whose waste must be regulated - are there to stay, Strand wishes that what he calls "extremist" environmentalists would leave his city alone. He said he already succeeded in keeping some waste treatment centers out of Chester, and now works with the remaining companies, cooperates with city officials, and makes sure that facilities comply with regulations.

"I'd rather have them take it to the suburbs and let the rich people deal with them," Strand said. "But right now, it is what it is. I have to deal with it and make the best of it."

Covanta, which operates the trash incinerator, wants to put up two new buildings at its site along the Delaware River. The plan would not increase the amount of waste coming into Chester, and would allow the company to rely on safer containers to transport trash, said John Waffenschmidt, Covanta's vice president for environmental science and community affairs.

"We have a minor application to make a small change at our facility," Waffenschmidt said. "We are a good corporate citizen in Chester on a number of fronts, and our facility is fully compliant from a state and federal standpoint. And we have rights. This is a property-rights issue."

The company says the plant, which began operating in 1992 and was purchased by Covanta in 2012, processes up to 3,510 tons of solid waste a day.

The changes to Covanta's facility would allow it to accept trash that comes by railroad from New York City to be burned in Chester, Waffenschmidt said. Trucks still would deliver the rail containers to the incinerator after they arrived by train, in Wilmington, and Covanta estimates its truck traffic will increase by only five vehicles per day.

But after protesters appeared at meetings this summer to speak about environmental and health concerns, the city's planning commission voted against the plans.

A spokeswoman for Mayor John Linder said Linder would not comment on the issue until after council votes, perhaps this week.

The residents who spoke out against the incinerator before planning commission and at a recent City Council meeting were organized by the Philadelphia-based Energy Justice Network.

Mike Ewall, the organization's founder, said he was working toward a goal of shutting down incinerators around the country because they harm the environment and residents' health. The first step for Chester, Ewall said, is turning down Covanta's latest proposal.

"It's just a priority because it suffers so much and there's so much important work to be done there," he said.

But whether - or how much - the health of Chester residents has suffered because of the incinerator or waste facilities would be difficult to document, experts say.

"There's so many unknowns with . . . making these kinds of analyses, and it's very hard to show causality," said Juliana Maantay, a professor of urban environmental geography at the City University of New York.

"We can pretty conclusively say you're more likely to end up in the hospital with an acute asthma attack if you live near one of these facilities," said Maantay, who researches and advocates for environmental justice and public health concerns. "But all the facilities are not equal. Some of them are run much better than others."

Such data are not readily available for Chester. But Ewall said he has spoken with many residents who struggle with asthma, and Strand agrees that health is a concern for residents near waste facilities.

Waffenschmidt, however, points to Covanta's compliance with state regulations, and cited other studies suggesting that well-regulated facilities do not cause public health problems.

Studies "talk past each other because they're trying to prove different matters," said Michael Churchill, a lawyer with the Public Interest Law Center of Philadelphia, which helped Chester activists take an environmental justice case to the U.S. Supreme Court in the 1990s. That case was dismissed by the Supreme Court after the solid waste company they had sued withdrew its application for a permit.

Still, cities such as Chester that already have air quality issues should beware of small changes, Churchill said.

Those closest to the facilities - neighborhood residents - have been largely on the sidelines of the debate. When Rasheeda Jones moved her family to Thurlow Street last year, she did not even notice the incinerator complex beyond the fences and trees at the end of her street.

"I didn't even look over there," Jones said.

She also did not know the history of her street, which years ago was part of the trucks' route to nearby facilities until Strand's group pushed them to find another route.

Jones does notice smells and noise, but she was not aware of health risks until environmental activists came knocking on her door this summer.

A few doors down, Carlotta Goldsmith said Thurlow Street may be near an incinerator, but it feels safer than other parts of Chester. She has lived on the same block for 13 years, and plans to stay.

"You deal with what you got to deal with," she said, "unless you can afford to move into a neighborhood where you don't have to deal with it."