(a) General rule.--Each investigating grand jury shall be composed initially of 23 members and have a minimum of seven and not more than 15 alternates. Subsequent vacancies shall be filled by substituting alternates for the members who are excused or otherwise unable to continue their service.
(b) Quorum and manner of action.--Fifteen members shall constitute a quorum and may conduct business for the investigating grand jury. A majority of the full investigating grand jury shall be required to adopt a report or issue a presentment.
(c) Officers.--The supervising judge shall appoint a foreman from among the members of the investigating grand jury. The members of the investigating grand jury shall then elect a secretary.