The Pennsylvania Department of Environmental Protection has ruled out faulty underground storage tanks as a possible cause of a spill last month that sent 4,700 gallons of gasoline from a gas station onto elementary school grounds and into a local waterway.

As a result, it said, the cause of the June 10 leak is still under investigation.

The leak was discovered the morning after a transport truck had filled underground tanks at the Gas ‘N’ Go on Coebourn Boulevard and Edgmont Avenue, in Brookhaven, Delaware County. The tanks had been filled about 10:30 the previous night, after the station was closed.

No one from the Gas ‘N’ Go was on the scene at the time Lee Transport Systems of Elmer, N.J., made the delivery, the station’s owner has said.

Jamar Thrasher, a spokesperson for the DEP, said Tuesday that the agency “has concluded, after multiple inspections by certified inspectors, that the tanks are in compliance with relevant statute and DEP regulations, and can be returned to service. The cleanup work continues, and DEP will be continuing to monitor the cleanup progress.”

The gas station sits on a hill that flows down parallel with the boulevard. During the spill, thousands of gallons of gasoline poured down the hill, across a wooded and grassy strip, and into a storm drainage system on the school property. The storm 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, environmental remediation firms had to dig up school grounds immediately next to the station to remove contamination, though the school itself was not contaminated. Students had to return to all-virtual learning the final week of school, and a kindergarten moving-up ceremony had to be changed.

After the spill, Lee Transport Systems said it had hired an outside firm to “investigate a root cause for the spill incident.”

Meanwhile, the cleanup continues, according to Thrasher.

“The responsible parties continue to remove impacted soil from the area of the release, including behind the gas station and in the storm water basin,” Thrasher said. “The school is monitored on a daily basis for vapors, but nothing of concern has been detected. Booms and spill prevention equipment continue to be maintained and inspected by the remediation contractors.”