216 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



that all three methods of flow appear to follow Bagnold's law of the cube of the wind 

 velocity, at least for the soils tested, a fine sandy loam and a heavy clay soil. The constant 

 C for total soil flow varied widely for different soils; the range in these experiments was 

 1.0 to 3.1. Chepil also measured the proportion of each type of flow on four widely 

 different soils. These results are given in Table 2. 



TABLE 2 Relative Portion of Three Types of Flow on 



Different Soils 



*Based on data from Chepil (1 945b). ■ 



It is apparent that the fraction of the total flow carried in suspension is considerably 

 higher on agricultural soils than on desert sands (presumably because of the availability of 

 the smaller particles). These studies showed that the logarithm of the flow plotted against 

 height was essentially a straight line and that relative concentrations of soil particles at 

 different heights remained the same with wind velocities ranging from 13 to 30 miles/hr 

 (6 to 13.5 m/sec). Presumably, then, the relative flows also remained constant. 



Chepil (1945c) also provided the sizes of the particles in the soils studied, between 

 <0.1 and 0.83 mm. The relative suspension flow vs. the fraction of particles <0.1 mm is 

 plotted in Fig. 1. The use of any other particle size range or cumulative percentages gave 

 erratic results. This may indicate the importance of the fraction of the smaller particles in 

 the soil in producing the suspension fraction. 



An important factor in the suspension fraction is the aggregate state of the smaller 

 particles in the soil. Particles in the submicron size range rarely exist as such in the soils 

 because they tend to either clump together or to adhere to larger particles and thus 

 become small aggregates. In fact, Chepil (1945b) states that particles smaller than 0.005 

 mm (5 )Um) do not exist as such in ordinary soils because they are aggregated into larger 

 individual grains. He adds also that single grains or aggregates 0.05 to 0.5 mm in diameter 

 have Uttle or no cohesive properties and are easily carried by the winds. This means that 

 contaminants in the soils, either as fine particulates or absorbed on the surface of soil 

 particles, will largely exist as soil aggregates and will behave in the same manner as the 

 soil. Chepil (1957) demonstrated the aggregation of material carried in suspension at 

 heiglits of 4 to 8 ft in a dust storm by sizing particles by sedimentation in CCI4 , a 

 nonpolar solvent that tends to preserve aggregates, and then repeating in water following 

 dispersion with sodium hexametaphosphate. The curves show the percentage of particles 

 smaller than a given value reaching zero at about 5 jum in diameter in a 1954 storm and 

 about 10 iJtm in a 1955 storm. By contrast, the dispersed samples showed 15 to 25% of 

 the particles smaller than 5 iim. 



An important factor in aggregation is the moisture content of the soil. This has been 

 investigated by Chepil (1956) and by Bisal and Hsieh (1966). Chepil (1956) has provided 

 a formulation for the soil flow taking into account the increased resistance to movement 



