[en] This document was prepared in support of an Aggregate Area Management Study of U Plant. It provides a technical baseline of the aggregate area and results from an environmental investigation that was undertaken by the Technical Baseline Section of the Environmental Engineering Group, Westinghouse Hanford Company (WHC), which is currently the Waste Site and Facility Research Office, Natural Resources, Bechtel Hanford, Inc. (BHI). It is based upon review and evaluation of numerous Hanford Site current and historical reports, drawings and photographs, supplemented with site inspections and employee interviews. U Plant refers to the 221-U Process Canyon Building, a chemical separation facility constructed during World War II. It also includes the Uranium Oxide (UO₃) Plant constructed at the same time as 221-U as an adjunct to the original plutonium separation process but which, like 221-U, was converted for other missions. Waste sites are associated primarily with U Plant's 1952 through 1958 Uranium Metal Recovery Program mission and the U0₃ Plant's ongoing U0₃ mission. Waste sites include cribs, reverse wells, french drains, septic tanks and drain fields, trenches, catch tanks, settling tanks, diversion boxes, a waste vault, and the lines and encasements that connect them. It also includes the U Pond and its feed ditches and an underground tank farm designed for high-level liquid wastes