Table 5. Soil Activity Factor Calculated From Soil Mass (% by Weight) and Plutonium Activity (% of Total Activity) for Resuspendible Fractions Soil Cum) Soil Fraction Activity Fraction Soil Activity Factor 0.04 0.03 0.43 0.03 0.04 0.92 0.75 1.33 2.19 0.50 0.99 4.27 0.12 0.04 0.34 0.28 0.14 0.49 2.33 3.50 1,44 0.50 0.91 7.27 0.19 0.09 0.72 0.45 0.14 0.40 2.42 1.56 0.56 1,00 1.00 4,54 0.29 0.10 0.59 0.40 0.09 0.51 1.38 0.90 0.86 0.98 1.00 3.14 Nevada Test Site - Area 13 < 2 2-5 5 = 125 Rocky Flats < 2 2-5 5 + 125 Mound Laboratory* < 2 2-4 4 - 125%* Oak Ridge National Laboratory < 2 2-5 5 = 125 *Data from Muller and Sprugel, 1977. *kaAssumes particles greater than 45 um to be less than 125 um. 108 ORNL sample appears to have the least potential hazard and RF the highest potential hazard. Lung Depositional Factor. The next consideration which must be taken into account is the inhalation and depositional character of the potential resuspendible particles. In modifying the size associated plutonium in the respiratory tract, the model deposition in the pulmonary region as defined by the Task Group on Lung Dynamics (1966) was considered. Although the nasopharynx, trachea, and the bronchial tree do filter resuspended particles, the rapid clearance of the particles reduces the potential hazard in these regions (Task Group, 1966). On the other hand, several models as reported by Volchok (1972a) ignore the particles larger than 10 - 7 um (mmad); the task group model includes the deposition in the pulmonary region of particles up to 100 um (mmad). To modify the soil activity factor, the values selected for depositional fraction in the pulmonary region and the soil activity factors were multiplied. The depositional fractions used in these calculations were 0.40 for the less than 2 ym size, 0.12 for the 5 - 2 um size, and 0,03 for the 125 - 5 um size. The value of 0.03 was derived by determining the mean particle size of the three fractions (125 - 53; 53 - 20; and 20 - 5 um sizes); the mass median aerodynamic diameter was 55 ym which correspond to 3% deposition (Task Group, 1966 (Fig. 14)). The value of 0.12 corresponds to 3.5 um mass diameter or approximately 5 ym aerodynamic diameter. The value of 0.40 corresponds to the deposition of particles with 0.2 um aerodynamic diameter. Although the value is arbitrary, changing the size to 1 ym or to 0.1 pm aerodynamic diameter changed the difference in the modified soil activity factor of the two extreme values (NTS and RF) by about 107%. In Table 6, the modified soil activity factors of the three resuspendible sizes are shown. The major effect of the depositional modifier is to minimize the importance of the plutonium associated with the coarsest size. Thus the RF, ML, and ORNL samples show a 6 to 7 fold reduction in the contribution of the 125 - 5 um size to the modified index; and the NTS sample show a 4 fold reduction. These reductions are compensated for by an increase in contribution to the modiffed factor by the finest size fraction. Although the overall numerical value of the modified soil activity factor is decreased as compared with the soil activity factor, the factors are ona relative scale and therefore should not affect the intercomparisons of the different sites. Resuspendible Activity Factor. The final factor to be considered in developing the overall soil is the amount of the total soil plutonium index activity in the resuspendible fraction. The soil activity factor considered the relative activity on the resuspendible sizes and the lung depositional factor took into account the depositional character of the particle sizes. It is also necessary to account for the amount of the total soil activity which is found in the resuspendible fraction of soil. Thus, the factor for a soil with 100% of the plutonium associated with the resuspendible size needs no further modification; whereas for a soil with only 50% of the activity in the resuspendible size, less plutonium is potentially susceptible to resuspension. Hence, the resuspendible activity factor is simply the fraction of the total activity in the 109