Nova Scotia Power is blaming a corroded pipe for allowing thousands of litres of oil to spill into Halifax harbour this past summer.

In a statement posted Wednesday to its website, the utility also said cleanup at its Tufts Cove generating station site is now complete after more than 24,000 litres of bunker C fuel leaked Aug. 2.

About 5,000 litres spilled into the harbour, while the rest leaked into a containment trench and a cooling water system.

"The oil leak was caused by a small section of pipe that failed due to corrosion," the statement said.

"The corrosion had thinned the pipe wall, which was under the pipe insulation. Since the leak, we have removed all pipe insulation and inspected every square inch of piping on our property to ensure it is in good condition."

The utility said it takes full responsibility for this "unfortunate incident."

"We take our environment commitments very seriously and we will apply what we have learned throughout the cleanup and subsequent investigation across our business to minimize the risk of something like this happening again," the statement said.

Questions left unanswered

The Ecology Action Centre in Halifax welcomed the update but said questions remain over how the pipe became corroded in the first place.

Mark Butler, the organization's policy director, said the utility told the centre Wednesday it would not be making its root cause investigation report public.

"We'd expected much more than what we got yesterday," Butler told CBC News on Thursday.

"They have said that they're not going to make the root cause report public and we question why, or we at least question why they couldn't release a lot more information. They're citing practice elsewhere and confidentiality."

Namely, the centre wants to know why the leak wasn't detected before the oil spilled into the environment, how often Nova Scotia Power inspected the pipe, and how the utility intends to deal with these issues going forward.

"We'd be interested in the cost of the cleanup and what that means for ratepayers," Butler said.

"And what seems to be going on here is an attempt to limit the dialogue around the spill and to share with the public why it happened and how they're going to prevent it from happening again."

Won't say how much cleanup cost

In an interview, Tiffany Chase, a spokesperson for Nova Scotia Power, would not disclose how much the cleanup cost because the incident is covered by insurance.

She reiterated the utility's commitment to the environment, saying it responded "quite quickly when the incident occurred and managed to contain the oil that did leak from the pipe."

More than 80 Nova Scotia Power workers and contract personnel worked on the emergency response effort to recover the oil from the harbour.

The final phase of work involved replacing approximately 150 metres of a rock wall directly in front of the power plant, where the remaining oil was located.