[en] Building 3515 at Oak Ridge National Laboratory (ORNL), also known as the Fission Product Pilot Plant, is a surplus facility in the main plant area to the east of the South Tank Farm slated for decontamination and decommissioning (D ampersand D). The building consists of two concrete cells (north and south) on a concrete pad and was used to extract radioisotopes of ruthenium, strontium, cesium, cerium, rhenium and other elements from aqueous fission product waste. Site characterization activities of the building were initiated. The objective of the site characterization was to provide information necessary for engineering evaluation and planning of D ampersand D approaches, planning for personal protection of D ampersand D workers, and estimating waste volumes from D ampersand D activities. This site characterization report documents the investigation with a site description, a summary of characterization methods, chemical and radiological sample analysis results, field measurement results, and waste volume estimates