DEVELOPMENT OF SPECIALIZED INSTRUMENTS AND TECHNIQUES FOR RESUSPENSION STUDIES Paul L. Phelps and Lynn R. Anspaugh Bio-Medical Division Lawrence Livermore Laboratory, California (Ed. Note: Previously published in NAEG Report NVO-142, pp. 221-233.) ABSTRACT An intensive study on the resuspension of plutonium at the Nevada Test Site has been initiated. The main thrust of the study is to develop a mathematical model for describing the concentrations of plutonium in air as a function of the source and driving forces. It is intended that the model be a basis for assessing potential health hazards and developing cleanup recommendations. In addition, the study is providing an opportunity to develop a generalized resuspension model, applicable in general for establishing environmental and biological assessment of nuclear projects involving plutonium. Apparatus and experimental techniques for studying the dynamics of plutonium and scil particle behavior have been developed. This has included the development of ultrahigh-volume air samples (1500 m3/hr) which allow collection of adequate samples of plutonium at worldwide air concentration levels in two hours of sampling time. We have also developed samplers for measuring the fraction of particles moving in creep and saltation. The Air Resources Laboratory, National Oceanic and Atmospheric Administration, has established an elaborate meteorological data-gathering system for measuring micrometeorological parameters, during sampling periods at the Nevada fest Site. Advanced optical methods for in situ sizing and counting particles have also been employed. This technique allows observations of particle size and concentration of a few-minute time scale, such that rapid changes in meteorological parameters may be more directly correlated with the concentration of airborne particles and their size distributions. The most intensive field program to date has been in the GMX area. Data have also been collected in Area 13 and Mercury. Ultrahigh-volume air samplers and high-volume cascade impactors were used to measure the concentration of plutonium in air and aerodynamic particle fractions of airborne soil and plutonium. Analysis of air samples collected by REECo from February, 1971, to July, 1972, shows that the GMX site, which was contaminated 17 years ago, still represents a significant resuspension source. However, the average air concentration of 273