[en] At the INL Site, the US DOE is planning to construct one of its largest CERCLA landfill covers. An evapotranspiration surface barrier that will be approximately 65 ha (160 acres) will cover the 39-ha (97-acre) Subsurface Disposal Area at the INL to isolate legacy mixed waste disposed of prior to 1988, low-level radioactive waste disposed of after 1988, and debris from demolition of structures being used to process some of the legacy mixed waste. The evapotranspiration surface barrier will limit percolation to less than 1 cm (0.39 in.) per year under typical precipitation conditions; provide a minimum 3-m (10-ft)-thick cover over all waste to minimize the potential for plant, animal, and inadvertent human intrusion; support growth of native vegetation; and visually blend in with the surrounding desert landscape. A robust design will allow the evapotranspiration surface barrier to resist erosion and perform for a minimum of 1,000 years. The 1-cm (0.39-in.)-per-year and 1,000-year performance objectives were established by a CERCLA record of decision and its implementing remedial design work plan, and these performance objectives are consistent with a performance assessment conducted under US DOE Order 435.1, 'Radioactive Waste Management.' (authors)