The natural near-field environment in and around the emplacement drifts of the proposed nuclear waste repository at Yucca Mountain, Nevada, includes the host rock, dust, seepage, and pore water. The chemical compositions of these components have been determined for assessing possible chemical and mineralogical reactions that may occur after nuclear waste is emplaced. The rock hosting the proposed repository is relatively uniform as shown by a mean coefficient of variation (CV) of 9 percent for major elements. In contrast, compositional variations of dust (bulk and water-soluble fractions), pore water, and seepage are large with mean CVs ranging from 28 to 64 percent. ?? 2007 Materials Research Society.