It will depend on your tax rate for the year based on your total income, filing status, deductions, and exemptions. Generally, a flat 25% is withdrawn for federal income taxes on supplemental pay such as a lump sum severance payment. So if 25% was withheld and your tax rate was only 15% then you would receive a refund of the difference.
The tax brackets are illustrated in the link below based on taxable income after deductions.
What has been the amount of federal taxes that have been withheld from your pay year to date? Has $166,985.92 ($85391.92 + $81,594) been paid to you year to date or is $81,594 what your salary would have been for the entire year? Do you have any other income such as investment income or unemployment compensation?
If your gross income is $138,918 then after deductions your taxable income ($119,618) places you into the 28% marginal tax bracket and there may be a small amount of AMT. I plugged the numbers into 2008 tax software to verify. So your refund may be between $1,100 - $2,000.
The 2009 tax bracket is in the link below:
See the rates for Head of Household - http://taxes.about.com/od/2009taxes/qt/2009_tax_rates.htm