Crews driving heavy equipment dug up layers of tainted soil at a Brookhaven, Delaware County, elementary school Tuesday following a weekend spill of thousand of gallons of gasoline from a gas station perched on a hill above.

The spill, the result of an as-yet unknown problem with a fuel delivery, killed dozens of frogs, turtles, fish, and even a fox along a nearby waterway. It contaminated a retention pond at the Coebourn Elementary School, where classes were scheduled to finish Friday. A kindergarten graduation ceremony had to be moved as the school remained closed.

Some of the estimated 4,700 gallons of spilled gasoline also seeped into a storm drainage system and a tributary of Chester Creek.

Representatives of the U.S. Environmental Protection Agency, Pennsylvania Department of Environmental Protection, and Delaware County’s Emergency Management and District Attorney’s Office of Environmental Crimes unit were all on scene Tuesday as the smell of gas still permeated the air.

Crews from two environmental remediation companies, Aquaterra Technologies and Lewis Environmental, were busy removing the soil at one border of the school, and cleaning up the school’s pond at another border.

“We’re trying to determine how far north, south, east, and west the gasoline went,” said Geoffrey Kristof, principal hydrogeologist with Aquaterra.

Workers had also installed a boom to contain the spill where the grounds drain into Shepard Run, a tributary of Chester Creek.

The dead wildlife had been collected, Kristof said, for examination by the EPA.

It’s not clear what caused the spill. Delaware County District Attorney Jack Stollsteimer said his office is investigating the incident to determine if anyone involved committed a crime.

» READ MORE: Delaware County DA’s office investigating Brookhaven fuel spill, which killed wildlife and contaminated waterways

Timothy Boyce, director of emergency services for Delaware County, said the county is looking into whether the spill was reported in a timely manner.

Boyce said Monday night’s heavy rain helped spread the gas. “As you dig up the dirt you can smell it more,” he said.

Gasoline on the soil’s surface will evaporate, he said, but benzene from the gasoline in the ground is “the longer term concern.”

Raj Syan, owner of the Gas ‘N’ Go, said the station closed at 10 p.m. Friday and no one was on the scene when a gasoline delivery was made about 30 minutes later by Lee Transport Systems of Elmer, N.J.

“We have never had a problem before,” Syan said.

As he spoke, crews were busy inspecting the tank near the back of the station where the gasoline was supposed to be stored.

Syan said the tank was sound, but that crews were “rechecking everything just to make sure.”

Fred Terpolilli, general manager for Lee Transport Systems, said he did not want to speculate on the cause, and said he has hired an outside firm to “investigate a root cause for the spill incident.”

The gas station at Edgmont Avenue and Coebourn Boulevard sits on a hill that flows down parallel with the boulevard. The gasoline made its way down the hill, across a wooded and grassy strip, and into a storm drainage system on the school property. The system flows under the school and into the heavily vegetated retention pond, which overflows into Shepard Run, then into Chester Creek, and eventually the Delaware River.

Because of the spill, students at the school had to go back to all-virtual classes for the last week of school.

George Steinhoff, superintendent of the Penn-Delco District, said the school itself was not contaminated.

“While the spill was extensive, preliminary information indicates that the leak did not impact the main parking areas, the building itself, or school playground,” Steinhoff said in an email. “However, the fuel spill did run into our stormwater management system which runs around the perimeter of a significant portion of the school, leading into a large retention basin. Air quality readings remain favorable within the school; however, there are quite a number of heavy duty trucks and machinery on site and in operation, preventing us from holding in-person classrooms.”

A kindergarten graduation ceremony scheduled for Wednesday was moved to the Brookhaven Municipal Building.