Experimentally Measured Resuspension Rates

DOE-HDBK-3010-94

4.0 Solids; Powders

surface from the atmosphere. Suspension is defined as the entrainment of particles on the

surface from nonatmospheric processes. The term resuspension is used to cover both

processes since, once the material is entrained, it is not possible to distinguish the behavior

of material generated by either process. For soil, the pollutant particles are attached to the

host particles. The data are insufficient to validate deposition, resuspension, diffusion and

transport deposition and airborne plume models.

Soil transport was extensively covered. Various equations are available to estimate soil loss

predominantly for agricultural purposes and are not particularly relevant here. Models based

upon wind stresses on individual soil particles are subject to formidable uncertainties when

required to integrate over the entire surface area. Due to the uncertainty as to the

applicability of these models, direct measurements of resuspension are preferred.

Table 4-19 lists some factors that may influence outdoor resuspension from soil. Not all

these factors are operative in any given situation and some factors may dominate in certain

regimes. The range of published resuspension factors for various aerodynamic and

mechanical stresses are shown in Figure 4-22 from Sehmel (1980) and are the same as shown

in Tables 4-16 and 4-17. Although shown together, it is difficult to compare the listed

values due to the differences in conditions and measurement techniques.

4.4.4.1.2 Experimentally Measured Resuspension Rates. Sehmel and Lloyd

(1976) reported the results of a 4-month study of the resuspension of a submicrom diameter

tracer from a lightly vegetated soil surface due to ambient wind stresses. An aqueous slurry

of submicron sized calcium molybdate stabilized with a surfactant was sprayed on the

surface of a lightly vegetated area in a circle with a 22.9-m radius on the Hanford site. The

surface roughness height was 34 mm. The average concentration over the area was 0.63 g

molybdenum/m2. Material resuspended were sampled by the arrangement shown

schematically in Figure A.37a using sampler as shown in Figure A.37b that aligned the

sampler inlet with flow. During the first two test periods (10/2/73 to 11/4/73 and 11/16/73

to 12/16/73) only one sampler was used at each height and all samplers operated

continuously. During the third test period (1/16/74 to 2/8/74), the sampling arrangement

was as shown in Figure A.34 and a single sampler at each height turned on automatically for

three velocity ranges (1.3 to 3.6 m/s, 3.6 to 5.8 m/s, and >5.8 m/s). The maximum

recorded gust during these periods was 20.1 m/s (45 mph). Samples were not taken during

periods of precipitation. The sampler inlet were isokinetic for a windspeed of 0.52 m/s.

Corrections for anisokinetic sampling are difficult to estimate for the continuous sampling

and are at least an order of magnitude less than the measured levels.

Resuspension rates for the test conditions were of the order of 4E-5/hr to 4E-7/hr. The

proper application required an equation that continuously depletes the source since there are

Page 4-96