HARRISON – Cleanup of oil-soaked soils continued Monday at a section of pipeline off the Upton Road where a leak was discovered by an all-terrain-vehicle rider Saturday.

But Department of Environmental Protection officials don’t believe a soil cleanup operation alone will be sufficient to remove the estimated 500 to 1,000 gallons of oil that were spilled. In addition to the soils cleanup, pipeline owner Portland Pipeline Corp. will be required to install a groundwater recovery system as well, the DEP’s David Sait, director of the Division of Response Services, said Monday.

Sait said the system involves drilling a well and then using a pump to move contaminated groundwater toward the well.

Sait said it’s unlikely the DEP will ever be able to say exactly how much oil spilled, and that the 500 to 1,000 gallons remains an educated guess. “It’s difficult to impossible to come up with a really accurate number” about the gallons spilled when a pipeline develops a leak, he said.

Since Saturday, contractors from Clean Harbors of South Portland have been at the spill site, just over a mile from where Upton Road intersects with Route 117. They had to excavate around 75 feet of the line in order to find the source of the leak, Sait said.

“When they finally found the leak, it was the size of a small hole” about a foot in diameter in the 2-foot diameter pipe, Sait said. “They put a clamp on it.” Because the pipeline pumps oil at very high pressure, Sait figured the leak developed relatively recently, based on the size of the spill.

The hole developed because that particular section of pipeline had been laid directly on rock, “a very large rock,” causing the steel to corrode over time, Sait said. He discounted theories that ATV riders and trucks riding over the pipeline may have weakened the pipeline, which is buried 4 feet deep.

Sait couldn’t provide estimates of the cost of the cleanup or how long it would take. “The length of the cleanup will depend on whether it represents any threat to drinking water,” he said.

A state hydrologist was on site Monday, and Sait said DEP officials are “relatively confident” there was no contamination to a nearby well, which is nearby but uphill from the spill site.

Similarly, Sait doesn’t think the spill has seeped into the Crooked River, which is over a half-mile away.

Spills along the pipeline route, which runs from Portland to Montreal, are “pretty infrequent,” said Sait, who couldn’t remember the last time a leak developed in the line.

Portland Pipeline did have some technical problems last year that required DEP attention, but those occurred inside its terminal in South Portland, he said.

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