Halifax Regional Municipality has applied for a six-month extension for commissioning permits for the Dartmouth and Herring Cove sewage treatment plants, signalling more delays for the region's troubled Harbour Solutions project.

The current application is the second time the city has asked for more time for the Dartmouth plant to meet its effluent discharge targets before it assumes ownership from the contractor.

An earlier year-long extension is set to expire at the end of this year.

"There are some underlying problems related to that … but the main issue is that there's still construction going on at the plant," said James Campbell, spokesman for the $333-million Harbour Solutions project.

The Dartmouth plant opened in July 2008 but is still being worked on. The Herring Cove plant, which was supposed to be turned over to the city in August, is currently in the early stages of testing.

Steve Westhaver of Nova Scotia Environment said the city has not been able to settle issues with the builder.

"They've not been able to sign off with their contractor that they've met the conditions of the approval, or that they've met the environmental requirements we would place on any operating approval," he said.

Westhaver said his department would not be issuing an approval until they can ensure the plants will meet environmental standards.

The $54-million Halifax sewage treatment plant — the largest of the three sites — has been largely out of operation since January when a power outage caused it to malfunction and the station overflowed with raw sewage.

It's not expected to be fully operational until next spring.