The mission of Waste Isolation Pilot Plant (WIPP) is to safely and permanently dispose of transuranic (TRU) radioactive waste generated by the production of nuclear weapons and other activities related to the national defense of the United States (U.S.). In 2004, 8,839 cubic meters (m3) of TRU waste were emplaced at WIPP. From the first receipt of waste in March 1999 through the end of 2004, 25,809 m3 of TRU waste had been emplaced at WIPP. The U.S. Department of Energy (DOE) Carlsbad Field Office (CBFO) and Washington TRU Solutions LLC (WTS) are dedicated to maintaining high quality management of WIPP environmental resources. DOE Order 450.1, Environmental Protection Program; DOE Order 231.1A, Environment, Safety, and Health Reporting; and DOE Order 5400.5, Radiation Protection of the Public and Environment, require that the environment at and near DOE facilities be monitored to ensure the safety and health of the public and the environment. This Waste Isolation Pilot Plant 2004 Site Environmental Report (SER) summarizes environmental data from 2004 that characterize environmental management performance and demonstrate compliance with applicable federal and state regulations. This report was prepared in accordance with DOE Order 231.1A, and Guidance for the Preparation of DOE Annual Site Environmental Reports (ASERs) for Calendar Year 2004 (DOE, 2005). The order and the guidance require that DOE facilities submit an annual SER to the DOE Headquarters Office of the Assistant Secretary for Environment, Safety, and Health. The WIPP Hazardous Waste Facility Permit (HWFP) further requires that the SER be provided to the New Mexico Environment Department (NMED).