Microfiltration and ultrafiltration (MF/UF) have evolved into widely accepted methods of water filtration and disinfection. Their evolution from industrial applications began with filtration of clean water supplies not requiring pretreatment to use on waters requiring significant treatment prior to filtration. Cost and system design innovations have led to the increase in the size of MF/UF facilities. In recent years, retrofits of granular media filtration facilities with MF/UF have been explored by researchers, engineers, and system vendors in order to reduce the cost of implementing the technology. Several examples of retrofit facilities with varying degrees of existing infrastructure reuse exist; however, many of the retrofit projects do not reuse equipment common to both MF/UF and granular media filters. The objective of this project was to investigate potential cost-saving infrastructure reuse options for membrane retrofits of granular media filtration cells. Of key interest was the feasibility of retrofitting granular media filter cells with membranes operating within the hydraulic gradeline of the plant, essentially a direct exchange of media filtration with membrane filtration. Originally published by AwwaRF for its subscribers in 2004.