to interest; provided, however, that for purposes of this section, such lien shall take effect by operation of law on the day immediately following the due date of such assessment or apportioned part of such assessment and such assessment may bear interest at a rate determined by the city or town treasurer by agreement with the owner at the time such agreement is entered into between the board of health and the property owner. In addition to remedies available under chapter eighty, the property owner shall be personally liable for the repayment of the total costs incurred by the city or town under this section; provided, however, that upon assumption of such personal obligation to a purchaser or other transferee of all of the original owners interest in the property at the time of conveyance and the recording of such assumption, the owner shall be relieved of such personal liability.