This Biennial Environmental Compliance Report (BECR), the eleventh to be issued,documents United States (U.S.) Department of Energy (DOE) compliance withenvironmental regulations applicable to the Waste Isolation Pilot Plant (WIPP), a facilitydesigned and authorized for the safe disposal of transuranic (TRU) radioactive mixedwaste. TRU waste is radioactive waste that contains alpha-emitting radionuclides ofatomic number greater than 92, with half lives longer than 20 years, and which arepresent in concentrations greater than 100 nanocuries per gram of waste.