PRC § 4052

The department shall keep a record of all expenditures against the moneys transferred to the fund for each project and any advances made pending federal reimbursement pursuant to subdivision (b) of Section 4051. Any unexpended balance for any project, either within three months after completion of the project or within three years from the transfer, whichever is earlier, shall be transferred to the credit of the fund from which the appropriation was made. The Department of Finance may approve an extension of the time allowed before a return transfer is required or require an earlier transfer to the credit of the fund from which the appropriation was made.