224 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



of the configuration and contamination level of the source. Anspaugh et al. (1975; 1976) 

 studied the resuspension of plutonium at the GMX Area in Nevada using an ultrahigh 

 flow-rate sampler so that samples could be obtained in a relatively short time while 

 meteorological conditions were relatively consistent. The resuspension rates measured 

 ranged from 2.7 x 10"^ ^ to 4.8 x 10~* ^ see"' . There was a strong correlation between 

 the resuspension rate and u|. Dividing the resuspension rate by ul greatly reduced the 

 variance found in the resuspension rate itself. This result is consistent with Shinn's value 

 for the dependence of dust flux on u* at this location. The value of the normalized ratio 

 to u^ ranged from 1 .5 X 10~^ ' to 10~^. It is noted that the pattern of plutonium in the 

 soil used for these derivations was determined by field instrument for the determination 

 of low-energy radiation (FIDLER) measurements of the ^'*' Am gamma (Healy, 1974) 

 converted to plutonium concentrations by statistical comparison of the plutonium and 

 americium content of soil samples (Eberhardt and Gilbert, 1972). This should provide an 

 estimate of the plutonium in the surface layers of the soil; so correction for plutonium 

 that has migrated to some depth is not required. 



The dust samples used by Shinn et al. (1976) in parameterization of the dust flux in 

 this area were also analyzed for plutonium (Anspaugh et al., 1976). The profile of 

 plutonium concentration at a distance of 100 m from ground zero (GZ) agreed with the 

 shape of the dust flux to a height of about 1 m and then showed lower concentratic^^ 

 than expected. At the 730-m point, the deviation is smaller. The deviations were as would 

 be expected for a limited source with rather abrupt discontinuities. However, the close fit 

 of the plutonium concentrations to the dust profile at the lower two heights indicates 

 that the plutonium concentration at a height less than 1 m is closely coupled to the 

 ground concentration, even though the soil contamination is less by two orders of 

 magnitude at the greater distance downwind. 



Saltation tluxes were also measured at the GMX Area (Anspaugh et al., 1976). Values 

 ranged from 3 X 10"'' to 8 x 10"^ g cm~^ sec~\ which are 10~^ to 10""* of those 

 measured by Chepil (1945a) for wind-eroded fields. In this connection Shinn (1977) 

 points out that NTS, the location of the GMX Area, is unique in that the natural 

 resuspension rate owing to convective winds is very low compared with more erodible 

 sites in the western United States. He has concluded that the natural desert shrub land, 

 covered by a "desert pavement," or the dry lakes, covered by a crust after a rain, are not 

 subject to wind erosion unless they are physically disturbed. 



Sehmel (1977a; 1977b) has measured the resuspension of plutonium at Rocky Flats 

 and of plutonium and cesium at the Hanford plant. However, the source areas are poorly 

 characterized; so resuspension. rates cannot be estimated. Various values of the power of 

 the increase of concentration with wind speed ranging from unity to 9.3 have been 

 obtained in these experiments; so it is difficult to draw conclusions from these data. 



Mechanical Resuspension. Mechanical resuspension is that caused by forces other 

 than the wind. Such forces could range from the movement of small animals on the 

 surface, through humans walking, to the movement of heavy equipment or plows across 

 the ground. There are several differences between mechanical resuspension and wind 

 resuspension, chief of which is the fact that the resuspending force is independent of the 

 wind speed (although dilution downwind will increase at higher wind speeds). Instead, the 

 resuspension rate will depend on the magnitude of the force applied as well, perhaps, as 

 on the nature of the force. A second difference is the depth from which resuspension can 

 possibly occur. In the case of wind resuspension, the layer from which particles can 



