presumably caused by the migration of be yo 19 /m. the initial surface-deposited material grated air activity {from t = 0 to o} for 239 Pu would be changed only by into the soil, Attempts to use the resuspension factor approach to derive acceptable levels of soil surface contamination have included this “attenuation factor" as a simple exponential function with half+ times of 35 or 45 days”? 4 There are However, the total inte- oo AX 104 f exp (- 0.693t/45d) dt ° eo +axi0 9 exp (- 0, 693t/24, 400y)dt 0 -3 = 6.5AX 107° -3 +1,34X10°°, major uncertainties in such a formulation, which is an increase of 20%, and more however. importantly, cannot be accumulated dur- The longest studyof this de- crease with time extended to only 11 mo following the initial deposition®, which ing an individual's life span. Because the functional nature of the is extremely short compared to the half2395. decrease in resuspension rate with time life of a radionuclide such as cannot be confidently extrapolated, pre- There are also published reports which viously. published models should not be indicate on experimental and theoretical applied to the recccupaticn of areas many bases thet the decrease with time will years after the contaminating event. not be adequately represented by a single The resuspensicn-factor approach can exponential function, but that the rate of be applied in an approximate way, hew- decrease itself will also decrease with ever, if resuspension factors are used . i time’ b Fortunately, the exact nature which were derived from measurements of this time dependence is not critical in over aged sources, determining the integrated exposure from relevant data are unpublished results the time of initial deposition due to the from current resuspension experiments fairly well-documented rapid decrease at at the GMX site in Area 5 of the Nevada early times. Test Site. However, it is obviously Perhaps the most The 2352p, at this location the controlling factor for questions con- was deposited following 22 high-explosive cerning the reoccupation of areas many detonations during the period from years after the contaminating event. December 1954 to February 1956, As an illustration, the most conserva- Measurements of resuspended air activity tive published model (Kathren®) may be levels at this site during 1971-1973 used to calculate a resuspension rate for appear to be the only available data con239 : cerning resuspension of Pufroma material 15 yr after deposition: K 1074 - m exp (83898. 15v X 365d \ TTS 45d ¥ = 10°41 /m, source of this age, Data irom two types or ineasurements are available and can be used to derive average resuspension factors, The first If, however, the resuspension rate type of measurement? was accomplished asymptotically approached some finite by placing five high-volume cascade value 10° § of the origina!, then the resus- impactors”® within the most highiy con- pension rate 15 yr later would obviously taminated area, and running them for 4-22 tuo an,