Furthermore, you were supposed to send 1099-INT annually to your tenant. Additionally, Under the Rent Security Deposit Act the landlord has to put a security deposit in a separate bank account that pays interest. The landlord must tell tenant in writing the name and address of the bank where the deposit is being kept, the amount of the deposit, the type of account, and the current interest rate for that account.
Looks like you haven't done that. One of the option is to go to the bank and ask them what was the escrow interest they were paying on average every year during this time frame. They will help to calculate total for you, most likely. You might also need to check on 1099-INT