(a) If a vacancy occurs on the commission, the commissioners court of the county in which the district is located shall appoint a qualified person to fill the vacancy not later than the 30th day after the date the vacancy occurs.
(b) If the commissioners court of the county in which the district is located does not appoint a member to the commission to fill a vacancy by the 30th day after the date the vacancy occurs, the remaining members of the commission may, by vote of the commission, appoint a replacement.