PLUTONIUM IN SURFACE SOILS OF AREA 13: A PROGRESS REPORT Tsuneo Tamura Environmental Sciences Division Oak Ridge National Laboratory ABSTRACT Analyses of three additional soil samples taken along a north-south transect in Area 13 gave mean plutonium values of 324, 132, and 166 dpm/g for the samples taken at 1,910, tively, from ground zero. 2,770, and 3,665 ft, respec- In all three samples, more than 65% of the plutonium was in the 53-20 um size fraction. Comparison of particle size analysis of two soil samples (one under shrubbery and the other without vegetative cover), with and without ultrasonic dispersion, showed that in both soils, contents increased with the treatment. the silt and clay The major change in plutonium distribution following the treatment was an increase in contribution by the medium silt size fraction and a decrease in the fine sand contribution. Although the field survey instrument (FIDLER) recorded a higher reading for the sample under shrubbery as compared with nonvegetated soil, the analysis showed that the nonvegetated soil had a higher plutonium content in the 0-5 cm depth. INTRODUCTION This report covers research progress during the 6-month period of October 1974 through March 1975. The objectives and scope of this program have been presented in earlier reports (Tamura, 1974, 1975a).