Senator Pamela Wallin, whose travel expense claims have been the subject of an independent audit, could be forced to repay an amount surpassing $100,000, CBC News has learned.

CBC national affairs editor Chris Hall said the long-awaited independent review being conducted by the auditing firm Deloitte, whose report will go before a Senate committee on Monday, will reveal that Wallin owes a much greater amount than the $38,000 she has already voluntarily repaid.

"The auditors with Deloitte have identified substantial amounts that could put the total repayment well into six figures," Hall reported Sunday night from Ottawa.

The amount relates to flights and taxi trips that were not strictly for Senate business. The audit goes back to 2009, when Wallin was sworn in to the Canadian Senate as a Conservative.

Frequent travel stops in Toronto

The focus of the financial review will be to determine how much of a hit taxpayers may have taken due to extra costs incurred by the Saskatchewan senator's preference to stop over in Toronto on her commutes between Ottawa and Saskatchewan. Wallin owns a condominium in Toronto and often stayed there overnight, rather than making the direct flight from Saskatchewan to appear in the capital.

Details of the full accounting of Wallin's expenses will be unveiled Monday morning.

The same Senate internal economy committee that will receive the Wallin audit has also looked into improper housing expenses claimed by three other senators: former Conservatives Mike Duffy and Patrick Brazeau, and Liberal Mac Harb. All four senators' finances — including a $90,000 secret payment from Prime Minister Stephen Harper's then chief of staff to Duffy to cover his expense repayments — have been the focus of a months-long scandal engulfing the upper chamber.

The RCMP is looking into the Duffy, Harb and Brazeau files, but so far has not requested a copy of the audit of Wallin's expenses.

In an interview in June with CBC News chief correspondent Peter Mansbridge, Wallin said that "bilking the system" was never her plan.

"These are my mistakes. I take ownership of them," she said. "I don't think I deliberately set out to use the system or abuse the system. I don't think that I was there for my own personal financial gain or to aggrandize myself in some way."

Wallin told Mansbridge she considered herself to be "very disciplined" about charges she expensed, adding that she doesn't treat people to dinner and charge it to the Senate.

Wallin left the Conservative caucus in May and has claimed more than $320,000 in travel expenses since September 2010.