240 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



Two different resuspension rates are used. For wind-caused resuspension, resus- 

 pension rates are reported as the fraction of particles resuspended per second. Thus the 

 total wind-caused resuspension is a product of the surface contamination level, the 

 duration of resuspension, and the resuspension rate. For local mechanical disturbances by 

 vehicular or pedestrian traffic, resuspension was measured each time a car, ^4-ton truck, 

 or person passed across the length of a 3-m-wide tracer-contaminated area. Thus traffic 

 resuspension rates are reported as the fraction of particles resuspended per pass. 



Particles 



Resuspension was measured for several types of particles. The plutonium particle size 

 distributions on soils at Rocky Flats and Hanford were uncontrolled. A forest-spray 

 operation provided an opportunity to measure resuspension of DDT as tracer particles 

 not specifically controlled for size. The controlled, inert tracer particles used were 

 submicrometer CaMo04 particles and ZnS particles with an 8-//m mass aerodynamic 

 equivalent diameter. 



Air Samplers 



Airborne resuspended particles were either sampled with total air samplers* or sized while 

 airborne with particle cascade impactors.f Particle cascade impactors were used for 

 plutonium and CaMo04 particles. 



The particle cascade impactor for sampling respirable particles was attached to a 

 rotating cowl, which allowed simultaneous sampling of larger nonrespirable particles. The 

 cowl-impactor system (Sehmel, 1973a) shown in Fig. 3 was evaluated by Wedding, 

 McFarland, and Cermak, 1977. Particles entering the 15-cm-diameter cylindrical sampler 

 inlet of the cowl either settled on the cowl floor or were drawn up into the impactor. 

 Particles settling on the cowl floor are called "nonrespirable" in this chapter. Respirable 

 particles entering the particle cascade impactor were separated into nominal aerodynamic 

 diameter ranges of 7, 3.3, 2.0, and 1.1 m, which are impactor stage 50% cutoff diameters 

 for unit-density spheres. Smaller particles were collected on an impactor backup filter. 



Results and Discussion 



Airborne radionuclide concentrations were determined at transuranic resuspension study 

 sites at Rocky Flats, Colo. (Sehmel, 1976a; Sehmel and Lloyd, 1976b) and the Hanford 

 area in Washington (Sehmel, 1977c; Pacific Northwest Laboratory, September 1973- 

 October 1974). In addition, some cesium resuspension data are reported for Hanford 

 (Sehmel, 1977c). In contrast to transuranic resuspension, tracer simulants (Sehmel, 

 1977b) were used to determine particle resuspension rates. Results for each set of 

 experiments are discussed separately. 



Radionuclide-Particle Resuspension On Site 



Airborne plutonium concentrations at Rocky Flats and Hanford were measured as a 

 function of particle diameter, wind speed, and sampUng site. Radionuclide concentrations 

 per gram of airborne solid were determined. 



^General Metal Works, Inc., model GMWL-2000-high-voltage air sampler with filter holder, 

 t Andersen 2000, Inc., model 65-100 high-volume sampler head. 



