* Regulators issue orders following 2011 spill
* Says employees restarted line despite leak alarms
* No fine levied
* Critics call action "slap on the wrist"
CALGARY, Alberta, Feb 26 (Reuters) - Employees at Plains All American Pipeline LP's Canadian unit disregarded leak alarms and restarted a ruptured oil pipeline as they caused one of the worst oil spills in Alberta's history, a report issued by the province's pipeline regulator found.
Alberta's Energy Resources Conservation Board issued four "high-risk enforcement actions" on Tuesday against Plains Midstream Canada as it wrapped up an investigation into the April, 2011, breach of the Rainbow pipeline. The spill on the pipeline released 28,000 barrels of crude oil in a wilderness area near the northern Alberta native community of Little Buffalo.
There were no further penalties from the board, which can only levy minor fines. It estimates the spill, which closed the line for 122 days, cost the Alberta economy C$850 million ($826 million).
"That's a huge economic impact and it was industry wide," said Darin Barter, a spokesman for the board.
The spill from the pipeline which takes crude from northern Alberta and the Northwest Territories to Edmonton was one of the largest in the province's history. It came on the heels of a number of other ruptures, including Enbridge Inc's high-profile 2010 spill near Marshall, Michigan, that caused U.S. regulators to characterize Enbridge employees as "Keystone Kops" because they failed to shut the pipeline after alarms sounded.
The ERCB said Plains Midstream also failed to shut down the Rainbow pipeline despite leak alarms sounding at its control center. The line was down and restarted three times before being finally closed more than eight hours after the initial alarm.
"Overall, the actions of Plains appeared to demonstrate a practice of placing higher priority on continued operation of the pipeline over any potential impacts related to a pipeline leak," the board said in its report.
The regulator said Plains Midstream Canada must implement new risk assessment procedures; conduct an emergency response exercise; and confirm that it has improved its backfill technique.
The board also ordered Plains to improve its crisis communications, saying its efforts to keep the public informed after the spill were substandard.
The company said it is reviewing the board's findings.
"Plains is carefully reviewing the ERCB's investigation report to determine whether any further findings and improvements can be applied to our operations," Plains said in an email signed by "Plains Communications". "We have finalized the results of our own detailed investigation and have applied those lessons learned to improve our overall operations."
The findings and the orders did not mollify some critics, who called for hearings into pipeline safety in Alberta.
"The ... report is a damning indictment of pipeline safety in Alberta as yet another pipeline company has failed to protect Alberta's environment and people and only received the lightest slap on the wrist," Greenpeace Climate and Energy Campaigner Melina Laboucan-Massimo, said in a statement.