The Treasurer of the District shall, within one week after a schedule is adopted or amended, notify the treasurer of each member municipality and the registered haulers of the District of the adoption of the fee schedule. The amount of assessment there under shall be paid to the Treasurer of the District within 30 days from the date of mailing of said assessment. In the event a member municipality or registered hauler shall fail to pay any assessment when due, then and in that event shall interest thereupon accrue at the legal rate then in effect.