This GIS dataset contains polygons depicting U.S. EPA Superfund Operable Unit boundaries. The operable unit (OU) polygons represent an individual OU’s perimeters, which are used to identify a portion of a Superfund site with which assessment and response actions are associated. CERCLA regulations (40 C.F.R. § 307.14) define an OU as a “discrete portion of a remedial response [that] manages migration, or eliminates or mitigates a release, threat of release, or pathway of exposure. The cleanup of a site can be divided into a number of operable units . . . [that] may address geographical portions of a site.” Determined on a site-specific basis, OUs may represent distinct geographic areas, media or releases. Note that OUs may overlap geographically when representing distinct media or areas of concern. OU boundaries become the building blocks of site boundaries. Superfund features are managed by regional teams of geospatial professionals and remedial program managers (RPMs), and SEGS harvests regional data on a weekly basis to refresh the national dataset and feature services.