Omohundro WTP in Nashville is undergoing a comprehensive set of upgrades. The Process Advancements Project was born with a focus on water quality, with an ambitious pilot launched in 2018 that led to selection of post-filter GAC contactors as the process upgrade. It has since evolved far beyond adding GAC to an existing plant. Metro Water Services (MWS) will use the opportunity presented by the process train reconfiguration to establish a plant that meets Nashville’s needs for generations to come, including a 66% increase in capacity, new pretreatment, modern filters, nearly 10X the existing on-site storage, and new pump stations. Several unusual elements shaped the design to make it unique among water plant projects. One such driver is history and culture. More than simply construction of new facilities, the project emphasizes preserving the extraordinary character of the site by leveraging existing facilities in creative ways. Omohundro was first developed in the 1880’s with the steam-powered pump station. The landmark building on the bank of the Cumberland River was long-since retrofitted with motor-driven pumps and still serves as the raw and finished water pump station for the plant. The 1920’s filter complex is the architectural centerpiece, with its terrazzo floors and brick arches. Not only does MWS value its history and architecture, but the plant’s place on the National Register of Historic Places limits on how the site can be developed. How can the project simultaneously honor these facilities while modernizing the plant overall? Another defining feature is commitment to sustainability. On track to achieve both Envision and LEED Platinum, MWS wants this project’s environmental impact to be a model for the industry. With historic preservation, sustainability, uncompromising process criteria, layered site constraints, and existing plant operations all seemingly at odds, a series of creative solutions emerged through an extended planning phase. For example, the old filter building will undergo a transformation to become deep-bed GAC contactors, and new modern filters will be constructed in a separate footprint. Additionally, stacked process structures and highly integrated spaces were the only way to meet objectives on the constrained site. Filters will be above clearwells, mechanical systems above process equalization, vegetated amenity spaces and operations staff offices above those, with 3.4 MW of on-site solar generation at the roof levels. With the three-year design effort now finishing, this presentation will cover how the series of insights during the early conceptual phases shaped the project’s trajectory. We will retrace the path taken by the project team as the site puzzle was gradually solved, and reflect on how early decisions led to unexpected challenges and opportunities. Emphasis will be on unique drivers and non-conventional process design solutions.