The 2009 flooding of Halifax's wastewater treatment plant was due to a technical error, not human error, a report examining the $11-million malfunction says.

The 25-page forensic audit, written in late June 2009 by Colorado company CH2M Hill but only released Friday, cost the Halifax Regional Water Commission about $150,000, commission spokesman James Campbell said.

"The report indicates that any intervention the operator could've tried to have made, of which they did many, could not have prevented the incident that did occur so there's no operator error at all," Campbell said.


A flooded wet well area on Jan. 14, 2009. (Halifax Regional Municipality)

Halifax Water said the delay in releasing the report was due to legal issues.

The $54.7 million Halifax plant malfunctioned after a power outage early on Jan. 14, 2009, causing raw sewage to flood the building and seriously damage mechanical, electrical and control systems.

Back-up generators kicked in during the outage, but one eventually overloaded and shut down. Four pumps shut down as a result, causing the station to overflow with raw sewage two metres deep. 

Raw sewage poured into Halifax harbour for a year and a half while crews worked to repair the plant, making significant design changes, including changing the load distribution on the generators and moving critical electrical panels to an upper floor.

The sewage plant reopened in June 2010.

Campbell said $10.5 million of the repairs was covered by insurance. He said Saturday that the total cost of the Harbour Solutions Project was originally budgeted at $333 million, and came in $3 million under.