On August 1, 1994, Rivera was promoted to the rank of brigadier general and named commander of the 81st Medical Group at Keesler Air Force Base, Mississippi. As commander, he was responsible for the provision of health care to more than 50,000 patients in the Keesler area and for providing referral and consultative services for an additional 605,000 beneficiaries in a five state region (Department of Defense Region IV). His responsibilities included ensuring the availability of major war-and peacetime medical readiness response forces and also the direction of all managed health care activities in DoD Region IV.