Auditor General Michael Ferguson will review the expenses of all senators amid the ongoing Senate spending scandal, CTV News has confirmed.

Ferguson had indicated in June that his office may scrutinize the expenses of every single senator.

On Tuesday, he met with the Senate’s internal economy committee to determine the scope and the depth of his audit, which will look at living allowances, travel and office budgets.

Ferguson’s involvement comes after independent audits of four senators’ books revealed close to $500,000 in improperly claimed expenses that must be repaid.

Mike Duffy, Patrick Brazeau and Mac Harb were found to have claimed living allowances that should not have been charged to taxpayers, while the auditors concluded that Pamela Wallin improperly expensed flights and travel costs.

All four senators must pay back the money in question. Wallin, the most recently audited senator, is on the hook for $121, 348.

She will also have to repay a “good portion” of nearly $21,000 in other questionable expenses related to “networking” events, CTV News confirmed Thursday.

The auditors left the expenses for those events up to “interpretation” by the Senate.

Sen. Carolyn Stewart Olsen, who sits on the Senate subcommittee that is looking at the Wallin audit, confirmed that the Saskatchewan senator will have to pay back additional money.

A Senate source has indicated that the exact amount will be determined in the next few weeks.

With files from CTV's Daniele Hamamdjian