OTTAWA -- The expert firm hired to review the safety plan for returning the Confederation Line to service following last weekend's derailment provided consultation services to the city of Ottawa during the construction of the light rail transit system.

The city of Ottawa announced Friday STV has been hired to undertake an "independent and impartial review" of the cause, actions, safety plan and return to service plan for the Confederation Line.

STV is a North American professional firm with more than 40 years' experience in the rail transportation industry.

The two-year-old Confederation Line has been out of service since Sunday after an LRT car derailed just west of Tremblay Station, damaging a train, the track and rail infrastructure.

Officials from STV will arrive in Ottawa on Monday, eight days after the derailment shutdown the O-Train, to begin its investigation. 

On Monday, the Transit Commission passed a motion to hire an independent expert to confirm the safety of the plan to return the O-Train to service.

"Once STV is on site and undertakes a preliminary assessment, Members of Council and the Transit Commission will be provided with an overview of STV’s work plan and anticipated timelines for the completion of the independent safety review," said Steve Kanellakos, Ottawa's city manager.

"Once STV is on site and undertakes a preliminary assessment, Members of Council and the Transit Commission will be provided with an overview of STV’s work plan and anticipated timelines for the completion of the independent safety review."

There is no word on how much the city of Ottawa is spending to retain the services of STV.

The memo states the city continues to work with the Transportation Safety Board and Rideau Transit Group to determine the cause of Sunday's derailment.

In a note on its website, STV said it was part of a joint venture that provided preliminary engineering and program management services for phase one of the LRT construction in Ottawa.  In 2016, STV was part of a consortium awarded a contract for the preliminary engineering and program management for the second stage of the O-Train.

City officials tell CTV News Ottawa STV was contracted to consult with the city during construction of the LRT line, but were not involved in the actual construction project.

Officials add STV knows the system well, and it will help them conduct a safety audit following last weekend's derailment.

Rideau Transit Maintenance said on Monday it could be three weeks before the system is repaired and full service resumes along the 12.5 km route. The city told CTV News Ottawa on Friday afternoon there is no update on when the train service could resume.

There were 12 passengers and a rail operator onboard a westbound train that stopped near the Riverside Drive overpass after a set of wheels left the track last Sunday. The derailment caused "significant damage" to the LRT car, the track and infrastructure.

On Tuesday, the Transportation Safety Board of Canada said the LRT train actually derailed before entering Tremblay Station at approximately 12:15 p.m. on Sept. 19, approximately 500 metres from where the train stopped.

"The train then departed the station in the derailed condition and continued over the rail bridge that traversed Riverside Drive before striking a signal mast and switch heater that were adjacent to and north of track 1," said the TSB.

Transportation Services General Manager John Manconi told reporters on Wednesday OC Transpo and RTG are trying to determine where the train derailed.

"I saw some of the video footage, I can't tell you where it derailed, nor can my rail experts that have been operating trains for a very long time," said Manconi.

The derailed rail car returned to the Belfast maintenance and storage facility on Wednesday afternoon for further inspection.