Plains All-American could have prevented last year pipeline release in Santa Barbara County, California, but it “failed on multiple levels to prevent, detect and respond to this incident,” The U.S. Department of Transportation said on Thursday.

The pipeline ruptured a year ago, on May 19, and released around 2,934 barrels of crude oil on land and beaches, and into the Pacific Ocean.

A year later, the investigation into the accident has been completed, and the U.S. Transport Department said that the direct cause of the pipeline failure was external corrosion.

The investigation found that several factors contributed to the severity of the release, including the company’s failure to protect the pipeline from corrosion, and the company’s failure to detect and respond to the pipeline rupture once it occurred, the Transport Department said in its findings.

“PHMSA’s investigation reveals that a number of preventable errors led to this incident, and that the company’s failures in judgement, including inadequate assessment of the safety of this line and faulty planning made matters worse,” said U.S. Transportation Secretary Anthony Foxx. “Millions of dollars have been spent to repair the substantial damage caused to the environment from this spill.”

“This report confirms our preliminary findings on the cause of this incident, and reveals that the operator failed on multiple levels to prevent, detect and respond to this incident, Now that we have completed our investigation, we will focus on enforcement options,” said The U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration’s administrator Marie Therese Dominguez, “While we will continue to work with other Federal and State agencies on civil and criminal actions. The bottom line is this pipeline will not be allowed to operate until we are satisfied that all of its safety issues have been appropriately addressed.”

Pipeline operator charged

Earlier this week, on Tuesday, May 18, Plains All American Pipeline and one of its employees were charged by a California state grand jury for alleged violations of California law in connection with the May 19, 2015 accidental oil release near Santa Barbara.

Plains noted that the indictment included a total of 46 counts, 10 of which relate to the release of crude oil or reporting of the release and 36 of which relate to wildlife alleged to have been taken as a result of the accidental release.

“Plains is deeply disappointed by the decision of the California Attorney General and Santa Barbara District Attorney to pursue criminal charges against Plains and one of its employees in connection with the 2015 accident. Plains believes that neither the company nor any of its employees engaged in any criminal behavior at any time in connection with this accident, and that criminal charges are unwarranted. We will vigorously defend ourselves against these charges and are confident we will demonstrate that the charges have no merit and represent an inappropriate attempt to criminalize an unfortunate accident,” the company said.