Tertiary treatment has become widespread in wastewater treatment plants, both to meet discharge standards for receiving water and to provide influent for advanced water treatment in arid regions. There are many approaches to tertiary treatment depending on the contaminants to be removed, and as a result, there are a wide variety of tertiary unit processes in operation around the world. The long-term success of these systems requires effective approaches for rehabilitation and operational optimization. In this study, the City of Los Angeles Bureau of Engineering, MWH, and Lee and Ro investigated the tertiary granular media filters at the Terminal Island Water Reclamation Plant in San Pedro, CA, to determine the causes of various operational issues and consider potential rehabilitation. It was discovered that the design and operation of the filters had several inconsistencies. The rehabilitation of the filters focused on resolving the identified issues and inconsistencies. Issues encountered included significant media loss, leaking valves, underdrain block failures, and inconsistent design elements built into operation of the filter.