AUGUSTA — The Greater Augusta Utility District has filled a large sinkhole that opened following heavy rain last week on Augusta’s east side.

On Thursday, a utility crew filled the approximately 8-foot-deep hole that opened next to a stormwater pipe at a Ballard Center parking lot off Arsenal Street.

A sinkhole opened Aug. 31 in the parking lot of the Ballard Center in Augusta following heavy rain. The Greater Augusta Utility District filled the hole Thursday and plans to repair the corroded stormwater pipe that caused the damage. Jessica Lowell/Kennebec Journal

“That is an exceptionally large hole in the ground, and we’re fortunate that this is uncommon,” said Brian Tarbuck, general manager of the Greater Augusta Utility District.

The hole, which spanned parts of two parking spaces at the hospital turned office building, had been marked off with traffic cones to warn of the hazard.

Tarbuck said the utility district learned of the hole Tuesday when a contractor for the Ballard Center asked the district about fixing the hole. Initially, the problem did not appear to be with the district’s infrastructure, but further investigation showed it was.

The sinkhole opened up Aug. 31, the same day heavy rain fell across the capital region.

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Stephen Baron, a meteorologist with the National Weather Service in Gray, said nearly 1 1/2 inches of rain fell during a storm that passed through the area before noon.

The automated station at the Augusta State Airport measured .91 inches of rainfall, Baron said, but a spotter reported 1.43 inches of rain had fallen.

“It happened within a couple of hours. It wasn’t an all-day thing,” Baron said. “It looks like it was in the span of an hour.”

The storm that moved through the region was typical of the storms that have popped up this summer, dropping about an inch of rain per hour, he said.

On the same day, officials in Hallowell closed part of Winthrop Street after pavement near the intersection of Winthrop and Water streets rippled and warped, apparently the result of a structural failure in part of city’s underground storm drain system.

According to the U.S. Geological Survey’s website, sinkholes are formed when material below the ground’s surface is removed, causing a sinking or collapse of the surface.

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In this case, Tarbuck said, the stormwater pipe that carries rainwater and storm runoff to the Kennebec River has corroded.

Because the 30-inch pipe has rotted, runoff has leaked into the area around the pipe, washing away soil and sand and causing the collapse.

“Back in the day,” Tarbuck wrote in an email, “people thought it was a good idea to make stormwater pipes out of corrugated metal, the same material a lot of culverts were made of.”

Those corrugated metal pipes, however, corrode when carrying water from heavily salted roads and parking lots.

Because of the pipe’s advanced corrosion, Tarbuck said the utility district will not be able to repair it by relining the pipe with a polymer.

Instead, the district can “slip line” the corroded pipe by forcing a slightly smaller pipe into the existing one. That way, Tarbuck said, no excavation is needed.

“If it goes well,” he said, “(it) should prevent any future sinkholes at that location.”

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