The McMillan sand filtration plant in Washington, D.C. is a significant industrial landscape that provided safe clean water to much of the capital during 1905-1985. At the outset, the McMillan Commission chose to make the plant and adjacent McMillan reservoir part of the park system it was mapping for Washington. Frederick Law Olmsted Jr. was appointed to landscape the tract, a task completed in 1920. Closed to the public since WWII, the site was abandoned when its operation ended. This thesis looks at its future by exploring the thickness of landscape and the site's discovered geometry. Peeling back its uniformly level 25-acre surface broken only twice by rows of concrete towers, its horizontal layers, vertical elements and strong grids are revealed, offering clues for new design strategies. Examples of how landscape geometries have been considered and works of landscape built elsewhere are reviewed. Recalling water's historically central role in the site, the latter's potential for demonstrating responsible stormwater management and other sustainable practices is emphasized. Local stakeholder interests and proven ingredients of successful urban parks are noted. A design process is outlined that exploits the earlier exploratory findings to reconcile the transition between old and new, deciding what to remove and what to add. Details are provided on the resulting new "memorial park" that both celebrates its history and responds to contemporary interests and needs of the 21st century urban landscape.