Fort Campbell, KY is home to the 101st Airborne Division of the US Army. The Fort Campbell (FCP) water and wastewater treatment plants were constructed in 1943 to provide potable water and wastewater treatment to the newly established Camp Campbell, which was renamed as Fort Campbell in 1950. Both treatment plants are still in use today. The WWTP utilized chlorine gas for disinfection until 1992 when one half of the chlorine contact basin was retrofitted with channels for the current UV disinfection system. The other half of the chlorine contact basin was filled with gravel and capped with a concrete pad. The UV disinfection system at the FCP WWTP consists of a Trojan UV 3000 system with four medium-pressure UV reactors split into two channels. The system is rated at 4 mgd average flow with a 16 mgd peak hydraulic capacity. The existing horizontal bulb reactors have served the facility well over the years, however at over 30 years old, the UV equipment has reached the end of its useful life and is being replaced with a new system. The existing UV channels are shallow at 4’0” of depth. Shallow channels can present a design challenge to retrofit with other styles of UV reactor, specifically those styles with angled bulbs that utilize deeper channels. Additional drivers for replacement of the existing UV system include frequent maintenance requirements and difficulty obtaining parts. UV equipment technology has advanced in recent years and options include low-pressure, high-output amalgam lamps requiring fewer lamp elements; high-efficiency, variable-output (60 to 100 percent power) ballasts; and automatic quartz sleeve cleaning. These advancements reduce the number of lamps and sleeves requiring maintenance and replacement, save energy, and reduce the need for manual scrubbing of the quartz sleeves in which the lamps reside. A life-cycle comparison of alternatives was developed to evaluate the replacement of the existing UV system. The comparison evaluated installing medium-pressure horizontal bulb UV equipment in the existing channels while the WWTP remains in service with the construction of new UV channels for a low-pressure high output inclined bulb system in the adjacent half of the chlorine contact chamber. Two horizontal bulb UV systems were evaluated to retrofit into the existing channels and two low-pressure, high-output inclined bulb UV systems were evaluated in new concrete channels. The inclined bulb systems have lower capital and operating costs than the horizontal bulb system, but the inclined bulbs systems have additional construction costs associated with new deeper channels. The horizontal bulb systems have more bulbs and have higher annual bulb replacement quantities than the inclined bulb systems. Capital costs and operation and maintenance factors for each system were evaluated other over a 20-year lifecycle period with an assumed 5% inflation per year. This paper will present the life cycle cost comparison of horizontal and inclined bulb systems evaluated for the Fort Campbell Wastewater Treatment Plant UV disinfection system and the cost and non-cost factors that influenced the selection of a UV system for design and construction.