Don Litchfield rolls down the windows of his white pickup so I can catch a whiff. “Do you smell that?” he asks. “We’re pretty much as close as you can get to what people say is the source of the odor.”

Here at Newby Island Landfill, where two 120,000-pound bulldozers and a couple of equally hulking compactors cull and crush a half-acre of trash into the landfill, the air is less pungent than from the promontory overlooking the waterlogged Alviso landscape. An earthy, wet wood scent from nearby furrows of curing compost mingles with the rotting scent of un-recyclable trash. Not exactly pleasant but not overpowering. Granted, this is a relatively windless afternoon, cool enough to temper whatever smells might intensify in the heat.

“What you smell really depends on the day,” says Litchfield, who manages six Republic Services landfills for throughout the state. “Some days there might be a gas leak, or stronger winds or just the heat.”

But from a plateau that overlooks the salty sloughs, sewage pools and another landfill, the scent in the air has decidedly turned. Litchfield points to a number of possible offenders.

“I’ve got a pretty good nose for this,” he says, adding that the stench that haunts Milpitas and nearby cities could be coming from 750 acres of open-air, sludge-drying pools at San Jose’s wastewater treatment plant. Or, he says, it could come from an anaerobic organics digestion facility, a composting operation on Zanker Road, a sewage pump station or the host of saline ponds and algae-thick marshes that flank Newby Island.

“Not to pick on our industrial neighbors, but it would be unfair to single us out,” Litchfield says. “My guess is that what you smell is a combination of things, a side effect of being in a heavily industrial region.”

After becoming the target of a citizen-led campaign to “Stop the Stink” years ago, Newby Island has been on the offensive since it applied for a land-use permit last fall to expand the height of the landfill from 150 to 245 feet and extend its closure from 2025 to 2041. Opponents of the upgrade say their casus belli is the stench. But there’s also concern that approving the permit would elevate the landfill—couched in a seismically active region—to an unprecedented height for the region.

In addition to approval from the city of San Jose, expansion would require a final go-ahead from CalRecycle, which is expected to hand down a decision any day now. It’s a safe bet the agency will greenlight the project, considering it’s approved every single permit in the past three decades.

But a petition to stop the expansion has drummed up nearly 16,000 signatures, including those of Fremont and Milpitas city officials who call the odor a threat to public health.

Odor complaints to the Bay Area Air Quality Management District have shot up precipitously in the past three years. The air district and city of Milpitas logged 1,223 odor complaints, while the air district fielded 764 this past January alone—primarily from Milpitas residents residents grousing about a range of smells that included “garbage,” “compost,” “rotten eggs,” “poo,” “bathroom” and “rotting vegetation.”

Dozens of people speak out against the landfill’s proposed expansion at public hearings. At a Jan. 27 CalRecycle meeting, some of the 29 people who decried the project broke down in tears, blaming the landfill for a range of ailments, such as nausea, asthma and even cancer.

Though located within San Jose city limits since it was annexed in 1968, Newby Island, with its grand plans to become the tallest landfill in the region, has elicited a groundswell of opposition from residents in Fremont and Milpitas, who say they have to deal with the brunt of the odor thanks to prevailing winds that waft northward. In 2012, Milpitas sued San Jose, claiming the city’s environmental review for the proposed expansion overlooked odor problems. But the case was rejected, as was a separate class-action lawsuit accusing the landfill operator of negligence for letting the smell proliferate.

“If Republic wants to be a good neighbor, they should withdraw their application … and agree to fund an odor study before any new permits in the area are granted,” says Joseph Weinstein, a Milpitas real estate agent who testified against Newby Island’s expansion before state regulators last week. “It is legitimate that there are odors coming from other areas, that’s why we want to have an independent odor study before any permit is approved.”

If San Jose approves the permit, the citizen coalition to “Stop the Stink” will change its name to invoke the city it blames for smells that have sullied Milpitas’ reputation: “Stop the San Jose Super Stink.”

Weinstein says that when the landfill was built in the 1930s, the region was sparsely populated. Now that it’s the gateway to Silicon Valley, with Cisco, SanDisk, Samsung and Tesla as neighbors, it has to be held to a higher standard, he says.

When the permit came up for discussion at a San Jose Planning Commission meeting in early December, scores of people showed up to protest at City Hall, prompting commissioners to delay a vote. Commission Chair Matt Kamkar expressed doubts about Newby Island’s claims that the smell comes from a variety of sources, primarily decomposing organic matter in the region’s murky waterways. “I’ll be frank with you,” Kamkar told Republic’s lawyers at the Dec. 10 meeting, “you’re blaming everyone else and you’re not taking any responsibility for your own operation. I don’t appreciate that. … There’s no question the landfill is generating some of the odor.”

Some of the residents who attended the December hearing started a Facebook page, Milpitas Odor Problem, which keeps tabs on the landfill and rallies residents to speak out against the expansion. A candidate in San Jose’s District 4 special election in April has even made the region’s perpetual “mal-odor” a focus of his campaign.

“For generations, we’ve tolerated this ghastly odor, airborne bacteria, rodents, feces and dangerous chemicals, all within less than one mile of residents,” Johnny Lee, self-appointed stink police and D4 contender, tells Metro. “It is time to close this toxic dump site.”

He adds, “I believe this is America and it should not smell like this in America.”

Erstwhile Congressional hopeful Ro Khanna has also jumped into the fray, stepping up as a liaison for the Warm Springs neighborhood of Fremont, where residents have been grousing about the stench for years.

“What I’d like to see is for the city of San Jose to deny the expansion permit,” Khanna says. “I want the city to require an odor mitigation study … to require the landfill to propose what they’re going to do to mitigate the odor.”

Litchfield says the backlash took him off guard. He thought the multi-million dollar stink-quelling measures in place—including deodorizing misters and 200 methane-catching pipes—would be enough to ingratiate the landfill to residential neighbors.

“In retrospect, maybe we should have done more outreach,” he says, suggesting that Newby Island could work with industrial neighbors to host a “Stop the Stink” tour of its own, a way of admitting shared responsibility.

Despite multi-million-dollar mitigation efforts, there have been lapses. During a pre-permit inspection last fall, state CalRecyle inspectors found an open-air bunker illegally stockpiling solid waste.

The waste was cleared out a couple weeks later, but a records check by regulators also connected Newby Island to odor problems by cross-referencing a complaint with wind patterns recorded at the time it was logged.

Litchfield agrees Newby Island, which he refuses to call a “dump,” could always do more to be “a good neighbor.” He says he plans to enlist “some of the best noses in the nation” to conduct an odor study and is considering using technologies like the “Nasal Ranger,” a “smelloscope” that sniffs out the source of a scent.

But residents of Milpitas and Fremont want the city of San Jose to pay for a review of its own, to make it as objective as possible.

“First let’s do a study, then we can think about expansion,” Khanna says. “That should be the starting point.