A team of workers digging near Five Corners this week discovered a patch of toxic, contaminated soil that may force a major environmental cleanup of the Beach Road extension area.

Contractors hired by the Massachusetts Highway Department found soil contaminated with gasoline and oil while digging on Beach Road extension next to the Wintertide Coffeehouse. The contractors were working on a drainage pipe project from Beach Road to Vineyard Haven harbor when they made the discovery.

The contaminated dirt has brought the drainage project to a halt as the state Department of Environmental Protection (DEP) attempts to locate the origin of the toxic materials and determine responsibility for the spillage.

“There is significant discharge of some type of fuel in this area, so we are going to investigate to see who are the responsible parties,” DEP southeast chief George Crombie said yesterday.

Yesterday, officials from Massachusetts Highway Department, Tisbury and DEP began looking for answers on two critical questions: Who is responsible for the contamination and who must pay for the cleanup.

Several officials contacted by the Gazette yesterday privately said they believe the origin of the oil and gas is the old Dukes County Garage, which operated for almost half a century and is now the site of the Wintertide Coffeehouse building.

The garage, which operated from the early 1920s to the late 1960s, served many automotive needs. It once housed a Buick showroom and was also home to a repair shop and gasoline pumps.

Sources said that if the oil and gas comes from the old garage, there is a strong chance that most of the soil surrounding Beach Road extension may be contaminated. If that is the case, it will result in a large and expensive clean-up project that may have the state, town and private parties scrambling to determine who must pick up the bill.

For now, however, top DEP and Tisbury representatives are saying little about the contamination discovery. Tisbury department of public works director Fred LaPiana called the source of the oil and gas “unknown.”

“The state is trying to determine the extent of the contamination,” Mr. LaPiana said. “We are working with the DEP and our local board of health to come to some conclusions on the issue, but it’s a little too early to project how big the project is.”

Mr. LaPiana said the exposed contaminated area — roughly 36 square feet — has been covered over and represents “no risk” to residents in the area. Nearby businesses, including the Black Dog Tavern restaurant, remain in operation.

But there may be a long wait for the cleanup to begin. Mr. Crombie said the process of determining responsibility for the cleanup is “complicated,” and may involve multiple parties.

“Basically, we do an investigation and try to determine the parties responsible, and then we issue them orders to hire a licensed site professional and have them follow through on the regulatory cleanup process,” Mr. Crombie said. “Technically, if there is pollution on your property, you are deemed the responsible party.”

Responsible parties could include the state and Tisbury — which must determine ownership of Beach Road extension — and maybe even the owners of the Wintertide building.

For its part, the Massachusetts Highway Department said it expects to be a key participant in the Beach Road cleanup.

“In terms of possibilities as to where it comes from, we believe there was a gas station in the area,” said highway department spokesperson Krissa Myers. “Right now we’re waiting for DEP, and we will comply with whatever DEP tells us.”

Meanwhile, the contamination investigation has brought the Beach Road drainage project — expected to last one month — to a standstill. The project was intended to alleviate flooding in the surrounding area.

But now the focus of the town has shifted from flooding to oil and gas spills that may be decades old.

“The majority of these [contamination sites] are the products of things that happened years ago, when people’s focus wasn’t really turned toward the environment,” said Krissa Myers. “Back then, education about the environment and how to care for it wasn’t what it is today.”

The Beach Road extension contamination is not the first prominent toxic discovery on the Vineyard. In 1989, petroleum waste was discovered by Oak Bluffs water department employees servicing water lines on Circuit avenue extension. The water department spent $30,000 to clean up the problem.

Recently, DEP began investigating a contamination site at Martha’s Vineyard Airport. The contamination is believed to have originated from an auto business, but Dukes County — the airport owners — may be held responsible for the cleanup.