REVIEW OF RESUSPENSION MODELS 213 



Resuspension Rate 



The resuspension rate is defined as the fraction of the contaminant present on the ground 

 that is resuspended per unit time by either winds or mechanical disturbance. Once 

 obtained, it can be used to describe concentrations at any point around a nonuniform 

 contaminated area by the use of point-source dispersion and deposition equations and 

 integration over the area. This potential use was illustrated by applying it to an area 

 contaminated with plutonium by a safety shot (Healy, 1974) and the inverse use at the 

 same area to obtain resuspension rates from measured air concentrations (Anspaugh et al., 

 1975). It was introduced for use in resuspension calculations by Healy and Fuquay 

 (1958), although in a crude form. 



Slinn (1978) has pointed out that the resuspension rate can be converted to a 

 resuspension velocity by multiplying by the ratio of the quantity of contaminant per unit 

 area and dividing by the volumetric concentration of the contaminant in the soil. Such^ 

 velocity is analogous to the deposition velocity with, however, a negative sign when 

 conditions are such that net resuspension occurs. 



Three techniques have been used to measure resuspension rates for a given area: (1) 

 measurement of air concentrations resulting from a known pattern of a tracer material on 

 the ground and inferring the resuspension rate from height profiles, which gives the total 

 transport, or from use of dispersion equations in known meteorology; (2) measurement 

 of air concentrations from an existing contaminated area and obtaining the resuspension 

 rate as given in 1 ; and (3) measurement of natural dust fluxes and relating these fluxes to 

 some association between the concentration of the contaminant in the soil and the dust 

 flux. The last method has been used only for wind resuspension. 



Wind Resuspension. A detailed body of knowledge exists on the mechanisms of the 

 movement of soils by wind through the classic studies of Bagnold (1943) on desert sands 

 and the detailed studies of Chepil (1941; 1945a; 1945b; 1945c; 1951a; 1951b; 1956; 

 1957; 1960), Bisal and Hsieh (1966), Woodruff and Siddoway (1965), U. S. Department 

 of Agriculture (1968), and MaUna (1941) on agricultural soils. These studies wall not be 

 reviewed in detail since much of the information is appUcable to the limited condition of 

 erosion of erodible soils. There are, however, data and concepts applicable to the 

 resuspension process, at least for the limited conditions of agricultural soil, and a brief 

 review of these is in order. 



The relationsliip between erosion and winds is complex; a large number of variables 

 affect the outcome, Chepil (1945a) listed the most important of the factors as related to 

 the three categories given in Table 1 . In the following discussion I will briefly describe 

 some of the more important findings applicable to the general problem of resuspension 

 from the extensive work on soil erosion. 



Soil movement across an eroding field is primarily from movement of the smaller 

 particles, usually less than about 1 mm in size. There are three mechanisms for 

 movement, and the particular size for each is somewhat dependent on the wind speed. 

 The heaviest particles move by surface creep or movement along the surface. Chepil 

 (1945a) noted that these grains were too heavy to be moved by the direct pressure of the 

 wind but were propelled by the impacts of smaller grains moving in the second method of 

 movement, saltation. In saltation the grains, after being rolled by the winds, suddenly 

 leap almost vertically. Some grains rise only a short distance, whereas others, depending 

 on the wind speed, can rise to several feet. They are then carried forward by the winds 



