Thousands of people in Pennsylvania are expressing concerns about the safety of a multi-billion dollar gas pipeline being constructed across the state. The $2.5 billion Mariner East 2 pipeline is being built alongside an older, smaller pipeline called Mariner East 1.

It will transport natural gas liquids (liquid forms of ethane, butane and propane) from a shale region in western Pennsylvania across the full width of the state, to a refinery complex at Marcus Hook, near Philadelphia, for export overseas. That's a distance of more than 350 miles.

Once completed, Sunoco has plans to add an additional pipeline. Altogether it's estimated the pipelines could transport up to 675,000 barrels each day.

A view of the Mariner East 2 pipeline under construction. CBS News

The oil company behind the massive project says it will add billions of dollars to the economy and create hundreds of jobs. But some residents say the payoff isn't worth the risk, reports CBS News correspondent Don Dahler.

In Exton, Pa., the pipeline runs right through town, passing through some of the most densely-populated parts of the state. Pipelines are not new to this region, but residents say this one is moving forward without having considered all the potential risks.

The sheer scale of the Mariner East 2 pipeline is best viewed from above, where a path has been carved into the landscape of Chester County, just over thirty miles west of Philadelphia.

An aerial view of construction of the Mariner East 2 pipeline in Chester County, Pennsylvania. CBS News

"Where the drill site now is used to be covered with beautiful big trees," said resident Virginia Verslake.

Another concerned neighbor, David Mano, showed Dahler a jar containing a chemical that came out of his water well.

Chemicals from drilling have turned up in David Mano's water well. CBS News

Dahler asked, "Did they tell you what the chemicals are in this?"

"This is bentonite clay, which is what they use to lubricate the drill bit," Mano replied.

When asked what she believed was the worst-case scenario, Verslake replied, "An explosion. If there were to be a leak in the pipeline, the gas escapes, it goes back into its gaseous state, It's odorless, it's colorless. As long as it goes undetected, it's just waiting for an ignition source to set it off. And if it explodes, the blast zone is anywhere from 1,000 to 2,000 feet."

According to a recent report -- paid for by Sunoco -- the project will add as much as nine billion dollars to the region's economy and add hundreds of construction and permanent jobs.

Verslake said, "There's no there's no amount of money, there's no number of jobs that is worth putting all these lives at risk."

"But they say they're not putting your lives at risk," said Dahler.

"Sure, of course they say that."

Both residents point to an independent risk analysis funded by a group of private citizens. It concluded that a leak of highly-pressurized liquid gas could result in a flammable vapor cloud that could spread up to 1,800 feet within three minutes -- burning anyone within 700 feet.

"You'd have to evacuate on foot, because you can't start a vehicle," Verslake said. "You can't even use your cell phone to call for help, because those things can set off the gas. So it's an impossible task. First responders can't build emergency response plans, [and] we can't prepare for this."

Nearby, Rebecca Britton worries about the safety of her family.

Resident Rebecca Britton. CBS News

"The best I can do to prepare for this risk is leave my kids' shoes by the door so we can run upwind, on foot, half a mile in the event of a leak? That's an unreasonable amount of risk to ask my family to take," she told CBS News.

In a statement to "CBS This Morning," Sunoco responded by saying: "This pipeline project was thoroughly vetted over the past 5 years by the appropriate federal, state, and local agencies" and that the company has "trained more than 2,300 first responders since 2013" adding that "all are prepared to handle any issues involving mariner east 2, or any other pipeline." (animation out)

Earlier this month, the Pennsylvania Department of Environmental Protection indefinitely suspended work on the pipeline for, among other things, "allowing the unauthorized discharge of industrial waste" and "failing to perform work according to permit specifications."

Over six thousand people have now signed a petition asking the governor to take a closer look at the pipeline's potential risks.

Pennsylvania Senator Tom McGarrigle says that while the pipeline is safe, the concerns of some citizens may have been overlooked.

"I think the gas companies, where they missed the boat, they didn't do enough education," Sen. McGarrigle said. "They needed to meet with these neighbors and just not go ahead with the construction. From now on, they need to sit down with these neighbors and explain everything."

A spokesman for Governor Tom Wolf told CBS News the suspension will remain in place until Sunoco meets the demands of the DEP.

As for the risk assessment asked for by residents? They deferred to the Pennsylvania Public Utility Commission, which told us it is "considering how to best address public concerns."