238 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



More recently, resuspension has been reported at study sites on the Hanford 

 reservation (Sehmel, 1977c; Pacific Northwest Laboratory, September 1973— October 

 1974). These sites were low-level liquid-waste disposal sites. 



Although environmental plutonium resuspension is receiving attention, resuspension 

 physics is poorly understood. Resuspension was early characterized by a "resuspension 

 factor." The resuspension factor is defined as the ratio of airborne pollutant 

 concentration (amount per cubic meter) at breathing height divided by the ground- 

 surface contamination level (amount per square meter). Thus the resuspension factor has 

 units of meters" ^ . Reported resuspension factors vary many orders of magnitude with 

 values from 10"* ^ up to 600 m"* (Mishima, 1964; Stewart, 1967; Sehmel and Lloyd, 

 1976a). Resuspension-factor variations have not been adequately explained as a function 

 of experimental conditions. 



Resuspension factors from about 10"^ to 10"^ m" * are often used in hazard 

 evaluations. The resuspension factor is useful since a worker's inhalation hazard is most 

 Ukely related to the local resuspension caused by his work activities within a 

 contaminated zone; however, resuspension factors are only a very rough estimate of the 

 potential airborne contaminant concentration since resuspension factors cannot be 

 accurately predicted. In addition to local resuspension, airborne contaminated particles 

 can reach workers from upwind contaminated areas. Hence both local and upwind 

 resuspension should be considered, but resuspension factors in either case cannot be used 

 in downwind transport models. 



The resuspension factor is an index of only the potential inhalation concentration and 

 not the total resuspension release rate from a surface-contaminated area. Resuspension 

 release rates are needed for source terms in calculating total downwind diffusion and 

 transport of resuspended particles. Only recently have particle resuspension rates been 

 measured (Sehmel, 1973b; 1975; 1977b; Sehmel and Lloyd, 1976a; 1976c). 



The objective of this chapter is to summarize reported resuspension rates (Sehmel, 

 1976a; Sehmel and Lloyd, 1976b) and parameters (Sehmel, 1977b; 1977c) determined at 

 the Pacific Northwest Laboratory between 1971 and early 1977. These include 

 plutonium resuspension measurements at Rocky Flats and at Hanford as well as results 

 from controlled tracer simulant source resuspension experiments. 



In these experiments airborne concentrations were measured as functions of wind 

 speed, airborne particle size, and wind direction, and the collected radionuchdes or tracer 

 simulants were determined per gram of airborne soil or solids. Particulate air samples were 

 collected as a function of wind speed to determine whether airborne radionuclide 

 concentrations increased at higher wind speeds, and concentrations as a function of 

 particle size were measured to determine the distribution of radionuclide particles 

 resuspended as individual particles or attached to host soil and sohd particles. In addition, 

 airborne radionuclides were normalized by the total amount of airborne solids to relate 

 concentration per gram of airborne soHd to concentration per gram of radionuclide on 

 the ground. 



Experiments 



The experiments for measuring particle resuspension reported here have been reported in 

 fuller detail in the following references: 



• Plutonium and americium from resuspension study sites at Hanford (Sehmel, 



1977c) (Fig. 1). 



