With oil running again through the Keystone Pipeline after a spill, federal investigators have determined that construction damage caused the accident.

Per an article in The New York Times,  the spill was likely caused by damage to a weight that was added to a portion of the pipeline when it was built in 2008. Says The Times:

The Pipeline and Hazardous Materials Safety Administration issued a corrective action report Tuesday on the estimated 210,000-gallon oil spill.

The report says a weight installed on the pipeline nearly a decade ago may have damaged the pipeline and coating. According to the report, weights are placed on the pipeline in areas “where water could potentially result in buoyancy concerns.”

The spill occurred on November 16 in a field in South Dakota. The pipeline, part of a 2,687-mile system that carries crude oil from Canada across the Great Plains of the United States, leaked 210,000 gallons of oil. It happened near the Lake Traverse Reservation, home of the Sisseton Wahpeton Oyate tribe.

TransCanada, which owns the pipeline, claims that the spill was “completely isolated” within 15 minutes of being detected. The company began operating the Keystone, which transports 590,000 barrels per day of crude oil from Alberta, Canada, to U.S. refineries, again on Tuesday (November 28), with reduced pressure.

The spill—and its suspected cause of construction damage—is particularly concerning for South Dakota regulators and government officials. It is the third major spill since the pipeline began transporting oil in 2010.

“I’m anxious about the future operation of the pipe and the potential for future leaks,” Gary Hanson, vice chairman of the South Dakota Public Utilities Commission, told Inside Climate News. “If there is a standard installation procedure for installing the weights, that may have created challenges in other locations on the pipe.” According to Inside Climate News, regulators “reiterated their right to shut the pipeline down after federal inspectors suggested the company is likely to blame.”

Amid concerns about the Keystone pipeline, environmentalists are also focused on the Keystone XL pipeline. On November 21, TransCanada obtained a permit to build this pipeline, which would be 1,100 miles long. Yet, as Colorlines reported, “Activists, tribal nations and local ranchers declared a partial victory after the Nebraska Public Service Commission rejected TransCanada’s preferred route for the proposed #KeystoneXL pipeline.” Efforts continue to pressure financial institutions to divest funding.