The grounds for removal of a member of a board are:
(1) inefficiency in office;
(2) nonfeasance or malfeasance in office;
(3) not having at the time of appointment or not maintaining during service on the board the qualifications for office described by Section 451.507;
(4) a violation of Chapter 171, Local Government Code, or Section 451.112;
(5) the inability, because of illness or disability, to discharge the member's duties of office during a substantial part of the term for which the member is appointed; and
(6) absence, without having been excused by a majority vote of the board, from more than one-half of the regularly scheduled board meetings that the member is eligible to attend during a calendar year.