One of the most senior bureaucrats overseeing the Canadian government's troubled Phoenix pay system is retiring.

Brigitte Fortin, an assistant deputy minister at Public Services and Procurement Canada (PSPC), will leave her post as of Jan. 28, according to an internal memo obtained by CBC News.

"We are writing to announce the retirement of Brigitte Fortin after more than 35 years of public service," the notice says.

"She has served our department in a variety of leadership roles in this branch since 2005, has had a remarkable career and has made significant contributions to the public service."

Fortin is one of several architects of Ottawa's payroll modernization plan, which has caused financial hardship for tens of thousands of public servants and their families. Workers have been underpaid, overpaid or not paid at all since Ottawa implemented the new Phoenix program last February.

As assistant deputy minister responsible for the accounting, banking and compensation branch of the department, Fortin had extensive involvement with the planning, launch and subsequent attempts to resolve problems related to Phoenix.

Fortin will be replaced by Alex Lakroni, a former assistant deputy minister who recently led the Canada Post Corporation Mandate Review.

"Alex will bring a strong track record of financial management to his new role," the memo says.

Department turnover

The announcement of Fortin's retirement comes after another senior bureaucrat involved in the Phoenix pay controversy was shuffled out of her role last fall.

Rosanna Di Paola was shuffled out of her role as associate assistant deputy minister of Public Services and Procurement Canada last fall. (Ashley Burke/CBC)

Rosanna DiPaola, who served as an associate assistant deputy minister at PSPC and also had extensive involvement with the pay modernization program, was relieved of her decision-making duties and given a new "special advisory" role.

Fortin did not personally respond to questions from the CBC about her retirement.

A spokesperson from her office, James Stott, said in an email that "Fortin's retirement was a planned, personal decision."

No managers have been fired as a direct result of the bungled implementation of Phoenix.

Pay problems continue

PSPC won't release the total number of employees who have experienced problems since the launch of Phoenix.

As of July 1, at least 80,000 workers had been paid incorrectly; however, the department won't say exactly how many employees have come forward to complain since that date.

PSPC officials have explained it is tracking the number of transactions being processed, rather than the number of people who have experienced problems.

The government missed its own self-imposed deadline to clear that backlog by Oct. 31, 2016.

At the department's last technical briefing on the Phoenix system, it said 10,000 employees were still waiting for their issues to be resolved.

The department blamed complicated cases, with problems that predated the new system for the slow resolution time.

Since pay problems gained national attention last summer, Ottawa has hired more than 200 compensation advisors to resolve pay issues and opened a call centre in Toronto to field inquiries.

The system was supposed to save the government $70 million per year as of 2016.

But because of the additional staffing hires, and other complications, problems have cost $50 million to fix.