[en] The US Department of Energy faces some unique challenges in its site characterization effort to determine if Yucca Mountain is suitable to house this nation's first high-level radioactive waste repository. Facilities are being designed and constructed for both surface-based testing (SBT), which includes drilling a number of test holes and excavating trenches and test pits into the mountain, and the Exploratory Studies Facility (ESF), which will be an extensive underground test laboratory. During construction and testing, the Yucca Mountain Project (YMP) must ensure that the ability to safely store waste for 10,000 yr is not compromised. The YMP has initiated a determination of open-quotes important to waste isolationclose quotes (ITWI) effort to determine which items and activities are important to the gathering of valid test data and which could have an effect on the natural barriers. Concerns include the potential effects of changing the site's normal water patterns, introducing foreign materials, damaging the unexcavated rock, etc. The project has now entered into the phase in which the design organizations perform detailed QA classification analyses on their designs and a YMP assessment team reviews those analyses. Raytheon Services Nevada has been responsible for designing, classifying, and grading SBT and the initial ESF systems