It’s tough to miss Seneca Meadows, New York state’s largest landfill: Rising nearly 300 feet tall, it’s almost as tall as the Statue of Liberty, including its pedestal.

A decades-old depository of millions of tons of garbage, sprawled over more than 350 acres, it’s an artificial overlook visible from miles away. For homes to the east, it causes an early sunset.

And then, of course, there’s its odor, an ever-shifting stench which has inspired comparisons to dumpsters and dirty diapers, rancid meat and rotting fruit, as well as online maps of where “it stinks.”

But for the past several years, it seemed as though the olfactory abuse might soon be ending: According to state permitting, the landfill was set to close at the end of 2025.

Now, however, the landfill’s owner, the Texas-based Waste Connections, has indicated in filings with the state that it wants approval to fill a 47-acre “valley” between two of the site’s gigantic mounds — enough to fill MetLife Stadium 10 times, at least — a project it estimates would last until 2040.

That project would raise the peak of Seneca Meadows by about 70 feet — roughly to the height of a 35-story building — making it one of the tallest man-made structures in upstate New York and an odoriferous outlier in the largely bucolic Finger Lakes region.

Residents in and around Seneca Falls have long complained about a bevy of problems related to the site, including truck traffic, choking dust and the potential for landfill runoff — known as leachate — to contaminate drinking water.

They recount tales of “trash blowouts” where an exterior wall of dirt collapses, resulting in a cascade of garbage. Flocks of pesky sea gulls, looking for free food, circle constantly, depositing their guano on roofs, cars and customers in nearby shopping centers.

Even supporters of the landfill, whose oldest sections date back to the 1950s, admit they’d love it if Seneca Meadows — and all its associated ills — wasn’t there.

“If we had to make a decision today, with what we know, then obviously there would be no landfill there,” said Michael J. Ferrara, the Seneca Falls town supervisor and a lifelong resident, who has backed the expansion plan. “But it’s been here a long time.”

Keeping the landfill open likely makes the company a better neighbor, he suggested.

“They’re not going to take the landfill with them: It will still be here, unfortunately,” said Mr. Ferrara. “If it’s open, they have to tend to it a lot more.”

Waste Connections representatives declined to comment on their critics or the “valley infill” project, which is currently being evaluated by the state’s Department of Environmental Conservation.

The site’s district manager, Kyle Black, directed a reporter to the Seneca Meadows website for details on current operations and the expansion plan, which the company’s initial application says is needed “to provide critically needed solid waste disposal services locally and for the state.”

That stream of garbage is undeniable: More than two million tons arrives yearly via thousands of trucks roaring off the New York State Thruway. According to the company’s 2021 annual report — the most recent available — that deluge of trash includes solid waste, construction debris and a category known simply as “sludge.”

The refuse comes from all over the state, and farther afield, but its single biggest source is New York City, which sent about a quarter of the total haul in 2021, averaging about 1,500 tons daily.

The plan to expand has prompted an outcry from many environmentalists and business owners in the two neighboring communities: Seneca Falls, known as both the birthplace of the women’s rights movement and a supposed inspiration for “It’s a Wonderful Life,” and Waterloo, which claims to be the birthplace of Memorial Day.

In February, hundreds signed a letter to Gov. Kathy Hochul, a Democrat, pleading with her to stop the expansion, noting a range of problems with landfills, including ample emissions of “climate-destroying greenhouse gases” like methane.

Others accuse the company of buying off town board members in Seneca Falls via large campaign expenditures on behalf of landfill-friendly candidates by a group known as Responsible Solutions for New York. The group received at least $195,000 in donations from Waste Connections since the beginning of 2019, according to state election records.

One of those winning candidates in 2021, Kaitlyn Laskoski, a Republican, denied that she knew anything about the Responsible Solutions group, saying she was “just as surprised” when she received mailers paid for by the group supporting her campaign. She added she had not formed an opinion on the expansion yet, saying she wanted to “ensure the proper procedure is followed.”

Earlier this month, there were signs that the expansion could face some official local opposition, when the town board — including Ms. Laskoski — voted to table a lucrative agreement with Waste Connections.

The leachate produced by the site — around 200,000 gallons a day, on average — is particularly troubling for activists like Joseph Campbell and Yvonne Taylor, two of the founders of Seneca Lake Guardian, a group which seeks to safeguard the waters of the Finger Lakes.

According to the company’s 2021 report, tens of millions of gallons of that leachate — tainted by toxic substances like arsenic and a range of dangerous chemicals — was collected and shipped to treatment facilities around the state, including to Buffalo, Ms. Hochul’s hometown. But environmentalists there and elsewhere have raised alarms about the ability of such public systems to handle some of those toxins.

“We’re an American viticultural area,” she said. “It supports a 60,000 job, $3 billion industry here, tourism and agriculture, which all depends on clean air and clean water for survival.”

The opposition also includes the landfill’s neighbor, Waterloo Container, a bottle wholesaler just across Route 414, whose employees have complained of “a sewer odor” that makes them nauseous and sends them scrambling to close warehouse windows.

Bill Lutz, the company’s president and a longtime local resident, said the landfill had profoundly altered “the complete environment in two townships.”

“They’ve changed the air quality, they’ve changed the temperature,” said Mr. Lutz, noting that the decomposition inside the landfill generates “so much heat” that Central New York’s punishing winter snows often won’t accumulate on the site.

A final version of the company’s plans are likely to be released in coming weeks and will face an array of state environmental reviews. Its prospects could be complicated by the state’s ambitious plan to reduce emissions, passed in 2019.

The Department of Environmental Conservation said it was reviewing hundreds of public comments it has received since the landfill expansion was proposed.

The trucking of rubbish upstate continues even as New York City has taken steps in recent months to try to address too much trash. In June, the City Council passed a package of bills that mandates curbside composting, and that established a target date of 2030 to eliminate all organic matter and recyclables from its waste stream.

Sandy Nurse, a city councilwoman from Brooklyn who sponsored several of those bills, says she supports closing Seneca Meadows.

“We just toss it out and think it goes away and it doesn’t,” Ms. Nurse said.

She noted that the city was spending some $450 million annually to ship its trash to other states as well as upstate New York.

Frank Sinicropi, another board member in Seneca Falls who backed the host agreement with the landfill, was blunt. “Ask the mayor of New York City,” he said, “where the city trash will go.”

Waste Connections seems well aware of the public relations challenges: The company has a complaints hotline, which results in a site visit by a landfill representative and a formal report, though some residents complain that those reports are usually deemed inconclusive.

The landfill managers also use a variety of methods to try to mitigate the odors, including aerators which release a flowery-scented mist along the periphery of the site.

The Seneca Meadows website says that the company works to collect the methane released by decomposition, using some of it to generate electricity, and adding that the waste it accepts is “nonhazardous.”

Mr. Black said in an email that the company provides dozens of jobs at the landfill and dozens more in construction and operations.

The company has been active in community organizations and events, including in late July, when hundreds of locals flocked to the Seneca Meadows Open House, lining up for a bouncy house and free barbecue chicken, a vintage car show and a demonstration of live falconry. (The company uses about a dozen of those black-eyed raptors to scare off the sea gulls).

Perhaps the most popular attraction were the tours of the dump that loomed above the open house, with buses slowly inching up the incline to the top, which offers impressive views of the landfill — and landscape — as well as the piles of shredded rubber tires used in the landfill’s liner system.

These outreach efforts have resonated with people like Bill Ryan, 74, a retired accountant and longtime resident of Waterloo, who said he believed that Seneca Meadows was a “wonderful thing for the community” — noting the jobs and various local events they supported, including the Friday night fireworks display at this year’s county fair.

Standing at the fairgrounds, just beyond the landfill’s boundaries, Mr. Ryan said that the complaints about the stink were overdone.

“Smell is a nuisance,” said Mr. Ryan, who was sporting a Seneca Meadows hat. “Smell is not a hazard.”

Audio produced by Sarah Diamond.