As preparations continue for the inaugural Grand Prix of Boston on Labor Day weekend, opponents are warning that new construction in a heavily polluted portion of the race course could be environmentally hazardous. But race organizers insist those concerns are misplaced.

The debate centers on the proposed expansion of Cypher Street, which would serve as the entrance to a pit-lane area connected to the South Boston Bypass Road. That area was formerly part of a hazardous waste site, and was partially capped to prevent the release of harmful substances.

At a public meeting held by race organizers Wednesday in South Boston, Fran Flaherty of South Boston worried that incorporating the area in question into a race course—where dozens of cars will travel at high speeds for hours at a time—could be hazardous to locals’ health.

“People aren't going to be rushed to the hospital two days, three days after the event,” Flaherty said. “But you know, it could be something that comes up like two years from now, three years from now."

David Lurie, an attorney for opponents of the race, made a similar point Thursday, after a City Hall meeting at which changes to Cypher Street and other local roads were discussed.

"There are high levels of PCBs within three or four feet of the soil in areas that they're building, widening that road," Lurie told WGBH News. "And we're concerned for the public health and safety that those PCBs are going to get disturbed by their construction."

PCBs, also known as polychlorinated biphenyls, are a family of industrial chemicals classed as probable carcinogens by the Environmental Protection Agency.

"This was a former junkyard filled with, amongst many other things, with electrical transformers," Lurie added. "It was a mess." 

But John Casey, Grand Prix of Boston’s CEO, said race organizers are being conscientious when it comes to potential environmental issues.

“We’ve been working diligently with all the state agencies about the environmental concerns, and we’re treading very cautiously through the process to make this thing happen,” Casey said. “And I think we're in a good place. I'm very happy with where things stand right now.”

 “We’re not doing any digging,” Casey added. “We're just expanding on the existing road. As long as we don’t put a shovel in the ground, I think everyone’s safe.”

A call placed to the Environmental Protection Agency Thursday was not immediately returned.

Before the construction of the Boston Convention and Exhibition Center, the authors of the book Calculating Risk: the Spatial and Political Dimensions of Hazardous Waste Policy offered a vivid account of pollution in the area in question.

“The site itself would probably rank among the more dangerous waste sites in our sample,” James Hamilton and W. Kip Viscusi wrote. “Regulators have documented the presence of PCB contaminants at the site. The hazards were so severe that pools of oil containing hazardous levels of PCBs were discovered in neighboring properties, and even residents two blocks away have reported that oil odors were coming from the site."

Grand Prix organizers plan to make additional road modifications in preparation for the event. Some of these will be temporary, others permanent.

Any lasting changes, organizers say, will be made in accordance with the city’s wishes.