Keystone Pipeline Kansas leak is latest in series of accidents since 2010

As investigators in Kansas seek to determine what caused the worst leak in the 12-year history of the Keystone Pipeline, a federal report released last year showed the crude oil conduit recorded 22 accidents between 2010 and 2020 and found the severity of spills has "worsened" in recent years.

The report conducted by the U.S. Government Accountability Office showed the previous incidents leaked a total of 11,975 barrels of crude oil, or a little over 500,000 gallons. Combined with last week's incident in Kansas, the pipeline has spilled a little over 1 million gallons of oil in a dozen years, enough to fill one-and-a-half Olympic-size swimming pools.

The most recent Keystone Pipeline rupture occurred last week in Washington County, Kansas, near the Nebraska border, sending 588,000 gallons of crude cascading down a slope and into a creek, according to the pipeline's operator, TC Energy.

The government accountability report indicates the Kansas spill is not only bigger than all the pipeline's previous leaks combined, but it's also more than twice as big as the second largest accidental spill to happen on the pipeline, a November 2017 leak near Amherst, South Dakota.

A barrel of oil is equivalent to 42 gallons, or about the size of a typical bathtub, according to the report.

The Kansas oil leak is now the biggest in the United States in more than a decade, but not the nation's largest. The 2010 Deep Horizon incident released 210 million gallons of oil into the Gulf of Mexico over a span of 87 days before it was capped, making it the worst oil spill in U.S. history followed by the Exxon Valdez supertanker accident in 1989 that dumped 11 million gallons of oil into Prince William Sound, Alaska.

Twelve of the 22 Keystone Pipeline leaks between 2010 and 2020 released fewer than two barrels oil into the environment. But four others released more than 50 barrels each and six met the federal government's criteria for accidents "impacting people and environment," according to the Government Accountability Office.

The report found that since 2011, leaks on the Keystone Pipeline have gotten bigger.

In April 2011, 16,800 gallons spilled from a leak in Sargent County, North Dakota. In 2016, an accident near Freeman, South Dakota, also leaked about 16,800 gallons. Roughly 19 months later, the Amherst incident occurred, leaking 276,864 gallons onto land reserved for wildlife and public use.

Three years later, 189,630 gallons of crude leaked from a section of the pipeline near Edinburg, North Dakota.

"Keystone’s accident history has been similar to other crude oil pipelines since 2010, but the severity of spills has worsened in recent years," the government report states.

The report found that four of the biggest Keystone Pipeline oil spills were caused by issues related to the original design, manufacturing of the pipe or construction of the pipeline.

In a statement to ABC News on Tuesday, TC Energy responded to the report, saying, "We take every incident very seriously. No incident is ever acceptable to us."

"Our focus is the safe operation of our system in an environmentally responsible manner. We make ongoing investments in pipeline monitoring systems, planned maintenance, pipeline integrity management and emergency preparedness," the company said.

The company said it has also implemented pipeline improvements, such as the deployment of state-of-the-art inline inspection technology.

The Keystone Pipeline runs 2,687 miles from Alberta, Canada, to refineries in Texas, Illinois and Oklahoma. On its website, TC Energy says more than 3.3 billion barrels of unrefined oil has been transported through the Keystone Pipeline since it was opened in 2010.

The leak in Kansas was first detected just after 9 p.m. on Dec. 7, about 20 miles south of a pipeline's Steele City, Nebraska, terminal. The leak in the 36-inch diameter above-ground pipeline prompted TC Energy to shut down the line.

The spill near Mill Creek, in Washington County, Kansas, was "contained" by about 300 people working at the site, TC Energy said in a statement Monday.

It remains unclear when the repairs to the pipeline will be completed and TC Energy officials said no timeline has been established for restarting the flow of crude oil through the line.

Third-party environmental specialists were among the hundreds of people who responded to clean up the mess using multiple vacuum trucks, booms, and additional resources, the company said. As of Monday evening, the company said it had recovered more than 109,000 gallons of oil from Mill Creek and that continuing air quality monitoring has found "no indication of adverse health or public concerns."

"Over the last several years, we have taken decisive action to implement measures to strengthen our approach to safety and the integrity of our system and will conduct a full investigation into the root cause of this incident, in cooperation with regulators," TC Energy said in its statement.