The activity in the surface sample (0-5 cm) of the soil contained approximately 20,000 dpm/g. Because this sample was highly contaminated, size segregation, which originally requires about 50 grams, was not performed. Segregation of a 5-10 cm depth sample was performed with and without ultrasonic dispersion treatment. The size distribution, plutonium content, and the contribution of each size fraction to the total soil activity are shown in Table 4. In contrast to the dry sieving technique reported by Little et at. (1973), these samples were wet-sieved. The less than 125 ym size fractions composed 41.5% of the weight and 82% of the activity in the soil without ultrasonic treatment, and 51.2% of the weight and 912% of the activity in the ultrasonified soil. The results of the nonultrasonified sample were similar to the results reported by Bernhardt. The fractionation reported by Bernhardt (1976) included only the less than 100 um sizes; and the 10 um notation referred to by Bernhardt is the size based on 1 g/cm? particle density. For silicate density of 2.65 g/cm?, the corresponding size is 6.1 um. The 100 um size is based on sieve opening size and is thus not affected by the choice of density, The sizes reported by Muller and Sprugel (1977) and Tamura (1976b) are based on the silicate density. The importance of the size association of plutonium with host particles has been recognized by many investigators (Volchok et al., 1972b; Healy, 1974; Anspaugh and Phelps, 1974; Engelman and Sehmel, 1976). The interest stems from the difference in the resuspendible nature of plutonium associated with different particle sizes. When resuspended particles are inhaled, the deposi-~ tional percentage of the particles in the lungs is a function of size and increases with decreasing size (Task Group, 1966). The following sections consider the different size associations of plutonium, with emphasis on the amaller sizes, and presents an initial attempt to develop an index for comparing the relative hazard of the four contaminated sites. Since the soil serves as a reservoir for resuspendible piutonium, the necessity for considering both soil and plutonium properties is evident in assessing any contaminated site. However, it should be remembered that many factors enter into the resuspension of soil into the atmosphere including climatologic, meteorologic, topographic, and soil factors. In this paper, the plutonium-soil particle size association, the lung depositional potential, and the resuspendible fractions are considered as modifying the potential severity index. Other soil properties are important in resus pension and must be considered before any final judgment is rendered in ass essing the severity of the contamination. Chepil (1945a) Lists properties of Structure, specific gravity, and ee ee a ee ee SOIL PLUTONIUM INDEX rO NoDonnan Aenea nata [a (Oo na nw — > 4 > a) e 4 8 © @ #* 8 * 8 COTA SAAN ad mn 1d a4 SOHN AOAMA “N 3 mame ABO Amante Nt |r [BS lf nN MANN tT ARAMNAMDAD Aaaaeme ny |r ie WINANMOAMN [oO oOo ba ~~ a a < — a] uw 3 u oO at ns Ne Sedat and cw a a .o AN ate fa) ANWTMONY aoe © © & #& aot oS . a a 2 oe ff +4 a “4 a o N pa ne NA OO AH st An dad ~ an _ | % c a ae oa we 104 qgooawsdne we ee * # # © © & # ANAM NOH W 4 daaa 100.0 of a soil from Rocky Flats. Table 4. Tamura size-segregated and analyzed the plutonium in the 5-10 cm depth sample t Wi th (A) and Without (B) Ultrasonic Treatmen Particle Size Distribution (by Weight} Soil From Rocky Flats and Plutonium Distribution by Size in a (5-10 cm Depth) time (20 min.), and the absence of water as an agent to maintain dispersion. Bernhardt (1976) also segregated a surface soil sample from Rocky Flats using sodium metaphosphate as a dispersant. Particles less than 100 wm averaged 43% by weight. This fraction contained 75% of the total soil Pu activity. oonnmonn mw NA ON = v retuo 94a ne: goonnonwn omnrt v SHAAN NN