Mont. Code Ann. § 85-1-322

The proceeds of the bonds of each series issued under 85-1-301 and 85-1-303 shall be placed to the credit of the appropriate construction capital projects fund, which fund shall at all times be kept segregated and set apart from all other funds. There shall also be credited to the appropriate construction capital projects fund all accrued interest upon the bonds and the interest received upon the deposits of moneys in the fund and moneys received by way of grant from the United States or from any other source for the construction of the works. The moneys in each construction capital projects fund shall be paid out or disbursed in such manner as may be determined by the department, subject to this chapter, to pay the cost of the works. Any surplus which may remain in any construction capital projects fund after providing for the payment of the cost of the works shall be added to and become a part of the appropriate debt service fund hereinafter provided for.