MEDFORD — Every few minutes, another large, black bus putters to a curb at the Wellington MBTA Station, where it joins a line of shuttles that await a steady flow of patrons and employees heading to the nearby Encore Boston Harbor casino.
On a recent morning, five of them queued up in front of the station, their engines humming, fumes spewing from their exhausts.
“Nobody has told us that we shouldn’t idle,” shuttle bus driver Carol Tilton said as she waited for passengers with her engine rumbling.
That may change soon.
The Conservation Law Foundation recently notified Encore owner Wynn Resorts and several transportation contractors that it intends to sue unless the companies take quick action to cease idling. The shuttle buses have run around the clock to MBTA stops, the airport, and other locations since the Everett casino opened in June.
The Boston-based advocacy group has accused the companies of violating the federal Clean Air Act and state regulations that prohibit excessive vehicle idling, which releases a soot that includes harmful pollutants such as benzene, sulfur dioxide, and nitrogen oxides. When inhaled, the exhaust can cause lung damage and aggravate conditions such as asthma and bronchitis, especially among children. Exposure has also been linked to increased incidence of heart disease, cancer, and premature death.
“The casino is a brand-new neighbor, and it’s already wearing out its welcome,” said Alyssa Rayman-Read, director of CLF Massachusetts. “There’s no excuse for shuttle buses sitting in already vulnerable neighborhoods pumping toxic fumes into the air. These companies must prove that they care about the health of their neighbors and put an end to this dangerous, unlawful idling immediately.”
In response, officials from Wynn Resorts promised that they would ensure their shuttles comply with the law. The casino’s 16 buses and other shuttles are operated by DPV Transportation, a charter service based in Everett.
“Earlier today [Monday], we spoke to our provider about eliminating idling,” Michael Weaver, a spokesman for Wynn Resorts, said after being contacted by the Globe. “We will work with them to ensure compliance.”
Officials from DPV Transportation did not return calls.
Weaver said the company has a good environmental record, noting that the shuttle program is designed to reduce traffic in the area. Wynn Resorts spent $68 million to remove toxic chemicals from the property, the former site of a chemical plant.
“We believe our commitment to a clean environment is clear,” Weaver said.
The foundation also notified Paul Revere Transportation, a Roxbury-based company that operates shuttle buses in the area, that it also faced a lawsuit without prompt action.
Over the past two months, investigators observed the company’s buses near the Ruggles and North Station MBTA stops routinely idling more than five minutes, the limit allowed by state rules.
Officials from Paul Revere Transportation, which has been forced to pay federal penalties at least twice for excessive idling, didn’t respond to requests for comment.
The foundation said its investigators have also observed Wynn Resorts’ shuttles violating the law “on many occasions” near the Chelsea MBTA Silver Line stop, the Academy Express lot in Braintree, and by Boston University Medical School.
The foundation told Wynn Resorts and Paul Revere Transportation that it would seek the maximum penalties allowed under the law — nearly $100,000 a day — unless the companies complied within two months.
This isn’t the first time the foundation has sought to curb idling. In July, it sued Transdev, the transportation vendor for the Boston Public Schools, saying its investigators had observed 42 instances of parked buses running up to 49 minutes longer than allowed.
Over the past decade, state environmental officials have issued 43 notices of noncompliance for idling to companies or large organizations. In addition, they’ve issued four penalties that amounted to nearly $500,000.
Most of those fines were assessed in 2010 and 2014 to First Student, a school bus transportation company based in Ohio.
“MassDEP is committed to enforcing the Commonwealth’s idling regulations to protect air quality,” said Ed Coletta, a spokesman for the Department of Environmental Protection.
Madeleine Scammell, an associate professor of environmental health at Boston University, called it “disappointing” that the casino’s shuttles are spreading pollution in an area already dealing with smog from heavy traffic and industry.
Children are particularly susceptible to harm from inhaling exhaust, as they breathe far more air per pound of body weight than adults, she noted.
Idling was already a concern in the region, where asthma rates are high compared to the rest of the nation. In Massachusetts, 10.5 percent of residents suffer from asthma, compared to 8.2 percent of all Americans, according to state statistics.
Admissions to hospitals for asthma have also been rising in Massachusetts. In 2002, hospitals in the state charged $57 million for treating asthma; by 2013, those costs had nearly doubled, according to the Massachusetts Center for Health Information and Analysis.
“It is a well-established fact that vehicle exhaust is bad to breathe,” Scammell said. “That is why there are laws meant to prevent emissions.”
The same emissions are also a primary cause of global warming, she noted.
At the Wellington Station, many of the buses wereidling for longer than five minutes.
For many of the drivers, who make about 15 runs to and from the casino in often 12-hour shifts, the fumes are as much a part of the job as their black suits and ties.
One driver, Rodney Jamble, said he usually sits in his bus at the station for seven or eight minutes between runs. If he shut the bus off, that would often mean sitting in the cold or the heat.
“This is what we do,” he said.