However, two approximate methods may "under quiescent conditions, or after be used — the resuspension factor ap- administrative control has been established proach and an argument based upon in the case of an accident. " ambient air particulate concentrations, 10°°/m is suggested under conditions of with the assumption that the particulates moderate activity. are derived from the contaminated sur- ever, that exceptionally higher values face. (mean of 10° °/m) were observed during The former method has been fre-~ A value of Stewart states, how- quently used, but almost always in the the Hurricane Trial (Monte Bello Islands) context of a fresh surface deposit. and credited this to the nature of the The latter method is inappropriate to the small islands exposed to sea breezes, fresh deposit situation, but should be Values approaching 10° 3/m when dust is reasonably valid after enough time has raised by pedestrians and vehicles are elapsed for the surface-deposited mater- also reported by Stewart. Kathren® has also considered the re- ial to become fairly well mixed with a suspension factor approach and has few centimeters of the soil surface. recommended the use of 10 7/m asa as Resuspension Factor Approach conservative but appropriate value for The resuspension factor, K, is defined setting standards for PuO, surface contamination, 3 K = Air concentration (Ci/m”™) , Surface deposition (Ci/m?) and thus has units of m}, Langham 4,5 has suggested that a value of 10° °/m is a reasonable average It is almost - value to use in estimating the potential always implied that both measurements are made at the same location. The diffi- culties with this approach are fairly to 10° ‘jm and reports that his own the particle-size distributions of the con- measurements in 1956 produced a value taminant and the soil surface, vegetation of 7X10 °/m, Stewart! and Mishima” These recommended values, however, have tabulated values of K from many are all intended for application during the experiments including those involving time period immediately following deposi- laboratory floors as well as native soils. tion. As would be expected, the tabulated values cover an enormous range and vary Most of the high values, however, are derived trom experiments with laboratory floor surfaces and/ or with artificial disturbance, . . For outdoor situations, Stewart” 1 Numerous studies 1, 5-8 have shown that air concentrations of resuspended materials decrease with time, With the assumption that this decrease can be represented hy a singic exponential function, half-times of 35 to 70 days have been reported”? 7,8 sug- At the same time, ‘measured values lie in the range of 107° geometrical configuration of the source, from 107° to 10° 3/m, contaminated area. however, Langham notes that many obvious — no allowance is made for the cover, etc. hazard of occupancy of a plutonium- This decrease in air activity is not explainable by the gests as a guide for planning purposes relatively minor luss of material from that a value for K of 10° °/m be used the initial site of deposition’ 6 but is > TY_tA at