Samples of ash from the 18 May 1980 eruption of Mount St. Helens were collected from several locations in eastern Washington and Montana. The ash was subjected to a variety of analyses to determine its chemical, physical, mineralogical, and biological characteristics. Chemically, the ash samples were of dacitic composition. Particle size data showed bimodal distributions and differed considerably with location. However, all samples contained comparable amounts of particles less than 3.5 micrometers in diameter (respirable fraction). Mineralogically, the samples ranged from almost totally glassy to almost totally crystalline. Crystalline samples were dominated by plagioclase feldspar (andesine) and orthopyroxene (hypersthene), with smaller amounts of titanomagnetite and hornblende. All but one of the samples contained from less than 1 percent to 3 percent free crystalline silica (quartz, trydimite, or cristobalite) in both the bulk samples and 1 to 2 percent in the fractions smaller than 3.5 micrometers. The long-lived natural radionuclide content of the ash was comparable to that of crustal material; however, relatively large concentrations of short-lived radon daughters were present and polonium-210 content was inversely correlated with particle size. In vitro biological tests showed the ash to be nontoxic to alveolar macrophages, which are an important part of the lungs' natural clearance mechanism. On the basis of a substantial body of data that has shown a correlation between macrophage cytotoxicity and fibrogenicity of minerals, the ash is not predicted to be highly fibrogenic.
to the Log of the Activity of Fe3+ Versus pH (lA), and Plot of the Log AP/K Versus pH for Alunite (lB). 54 Plot of the Log AP/K Versus Sulfate Concentration for Gypsum (2A) and Celestite (2B) 58 TABLES Characterization of the Morton Ranch Clay Liner and Overburden Materials from the Morton Ranch, Dawn, and Lucky Me Mills •
The Office of Civilian Radioactive Waste Management (OCRWM) of the U.S. Department of Energy {DO£) has a mission to provide for the permanent disposal of radioactive wastes in deep geologic repositories. The OCRWM is currently developing a performance assessment strategy for demonstrating compliance with the safety and performance criteria developed by the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Environmental Protection Agency (EPA). Because of the long time (more than 10,000 years) involved, the OCRWM performance assessment strategy necessarily relies upon computerized models of the geologic repository system and its components.
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