Senator Mac Harb owes about $230,000 in expenses claimed improperly, the outgoing chair of the Senate's internal economy committee says.

Conservative Senator David Tkachuk told the CBC's Laurie Graham this afternoon, "Senator Mac Harb owes $240,000." When asked for more information, Tkachuk would only add, "I know because I wrote the letter to Mr. Harb myself."

His office later clarified the total as being $231,649.07. The total for living expenses adds up to $179,207, including interest. For mileage claims, the total is $52,441, also including interest. These amounts date back to the year 2005-06, according to Tkachuk's office. Harb was appointed to the Senate by former prime minister Jean Chrétien in 2003.

A Senate report last month ordered Harb to repay $51,000 in housing and living expenses claimed over 18 months from April 2011 to September 2012, but also asked auditors to take a look at claims going back several years earlier.

Tkachuk, who is stepping down as chair of the Senate's committee on internal economy at the end of the week for health reasons, confirmed that Harb's new bill includes the amount of $51,000.

Harb, who resigned from the Liberal caucus in the wake of the May 13 Senate report, saying he would fight the findings in court. He is now sitting as an Independent and has retained Michel Bastarache, a retired Supreme Court justice, as his lawyer.

Harb had claimed a house he owns near Pembroke, Ont., as his primary residence and had charged expenses for maintaining a dwelling in Ottawa as a secondary residence. Senators who live 100 kilometres or more from Ottawa are permitted to expense up to $25,000 a year for the costs of having a residence in the capital close to their Senate workplace.

However, the Senate said that the rules around primary residences are "clear" and 'unambiguous," and ordered that since Harb spends most of his time in Ottawa he should repay money he claimed.

Harb was once an Ottawa alderman and then a Liberal MP for the riding of Ottawa Centre, and seems to have lived most of his life in the capital since he immigrated to Canada from Lebanon as a young man. He purchased the home near Pembroke in 2010.

He has argued that the rules of residency are not clear, and that as a senator appointed to represent Ontario he did nothing wrong as long as he lived in the province.

CBC News attempted to call Harb Wednesday afternoon but was told he was not in his Senate office. His lawyer, when contacted, said Harb will be making a statement within a few days.