Paid twice by university for "same" research: how to proceed? I'm a graduate student doing research in physics. Through this month, I had an NIH grant through the Engineering department. I was also covered by my advisor's NIH grant in physics, with possible backup from the Physics department in case of a shortfall. 

This month, I was paid twice, for different amounts&mdash;once, apparently, from the the Engineering grant for work done in Engineering, and once from the Physics department for physics research. The problem is that, effectively, they're the same research. I wasn't doing twice as much research, although there were minor additional projects and requirements for the engineering grant. This is the last month of the engineering grant, which may explain the overlap. 

How should I proceed? 


Keep the money? Could the university demand it be returned at a later date? Might I not get paid next month?
Keep only one of the payments, and try to get the other back to the university? Which one?
Return them both and try to get paid again? 
Something else?
If the university decides one of the payments was made in error, they will almost certainly demand it back, and if you don't repay it promptly, they'll likely take steps that you won't enjoy (e.g. withholding from your paycheck, suing you, firing you, etc; specifics will depend on their policies and local law).  So don't spend the extra money until the situation is clarified.  Keep it in your bank account.  If they're paper checks, don't cash or deposit them.

Contact your advisors in both departments and explain the situation.  If somehow you're entitled to both payments, you'll get explicit confirmation and then you'll know you can keep all the money.  If not, they can negotiate between themselves as to where the money should go, and they'll tell you how much to repay, to whom, and how.