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Cleanup under way at the Rainbow pipeline spill in northern Alberta.Ian Jackson/The Canadian Press

An Alberta energy regulator says an oil pipeline in northern Alberta can resume shipping crude after it was shut down because of a leak at the end of April.

The Energy Resources Conservation Board in a statement Friday said the Rainbow pipeline can return to service, and that it passed a "comprehensive review and assessment." Rainbow's owners now have to submit monthly progress reports and attend meetings with the ERCB to ensure it complies with regulatory requirements.

Rainbow, owned by Plains Midstream Canada, will not be running at full steam. The ERCB said it can only operate the pipeline at 75 per cent of tips maximum operating pressure at first. The regulator will monitor the pipeline's resumption. Further, Plains told the ERCB it implemented a weekly aerial surveillance plan to check for "geotechnical hazards."

While the ERCB gave its blessing, it said it continues to investigate the leak and will issue a full report later. The leak was caused by a crack at a weld-on sleeve, and Plains is now digging up and inspecting all sections of the line that contain these sleeves.

The 20-inch northern portion of Rainbow leaked about 28,000 barrels of light oil – the largest pipeline spill in Alberta in decades – into muskeg and ponds on April 28. Its cleanup was delayed by the forest fires that later swept Slave Lake. The pipeline ships about 220,000 barrels of oil per day. Plains Midstream Canada is owned by Plains All American Pipeline LP , and the ERCB on Aug. 16 issued a conditional approval for the pipeline's resumption.