REVIEW OF RESUSPENSION MODELS 229 



well as direct contamination of the larger soil particles by the plutonium-bearing oil that 

 was the source of the contamination. 



Tlie U. S. Environmental Protection Agency (1977) proposed the use of an 

 "enrichment factor" to include these data in resuspension calculations. This is defined as 

 the summation of the products of gi , the ratio of the fraction of the total activity 

 contained witliin the size increment i to the fraction of the total mass in the size, and f, 

 the fraction of the airborne mass within each increment of particle size in the air. For the 

 distribution in soil sizes at Rocky Flats, they calculate an enrichment factor of 1.5. 

 Tamura (1977) has defined a "soil plutonium index" which accounts for the size 

 distribution as well as the lung deposition. This is given as 



SI = SA X LD X RA (18) 



where SI = soil plutonium index 

 SA = soil activity factor 

 LD = lung deposition factor 

 RA = resuspendible activity factor 



Tlie soil activity factor is the fraction of the activity in a given mass fraction divided by 

 the mass fraction for particles less than 100 /jm. (Tamura used 125 iJ.m in evaluating this 

 factor because this was the sieve size used in his analysis.) Values of this factor range from 

 3.14 for the ORNL sample to 7.27 for the Rocky Flats sample. The lung deposition 

 factor is the deposition in the pulmonary region as defined by the International 

 Commission on Radiological Protection (1966). The final factor, the resuspendible 

 activity factor, is the fraction of the total soil plutonium index activity in the 

 resuspendible fraction. Indexes derived from available data give 0.52 for Area 13 at NTS, 

 1.26 for Rocky Flats, 1.18 for Mound Laboratory, and 0.69 for ORNL. 



Another approach to the use of the smaller particles is that of Johnson, Tidball.and 

 Severson (1970). Their sampling technique was to brush the surface dust into a container. 

 The 5-/jm or smaller particle sizes were then separated from the sample after aggregates 

 had been broken up, and plutonium analyses were performed on this fraction. They 

 found that the concentration in these small particles was 4 to about 300 times as large as 

 that in similar samples taken to a depth of Vg in. Their conclusion was that these results 

 provided a better indication of the hazard than the conventional sample, although they 

 did not explore mechanisms of breaking down the aggregates found in the soil, which 

 severely limit the quantities of particles of this size found in natural soils, nor did they 

 examine pathways o\' this material to man. 



These relations have never been actually tested to show their validity. The work on 

 soil erosion indicates the many additional factors that will influence wind erosion and 

 resuspension. These include the soil texture, the moisture content o\' the soil, the 

 presence or absence of vegetation in vegetative residues, and the characteristic surface 

 roughness. In the case of NTS. the desert pavement undoubtedly has more influence on 

 either wind or mechanical resuspension than the other factors. We would believe that 

 wind erosion, in particular, is more complex than these relations would indicate. 

 However, it is possible that such concepts may be more applicable to mechanical 

 disturbance. 



A direct test of the mass-loading technique has been made by Anspaugh, Shinn,and 

 Wilson (1974) and Anspaugh et al. ( l'-)75). The measured concentrations of a number oi' 



