Cs af \ ot There is no general model that can be used with confidence to predict the resuspended air activity in the vicinity of a soil burden of Pu. Two approximate approaches can be used to give an indication of the activity. These are the use of the resuspension factor and an argument based on average dust loading assuming the dust is derived from the contaminated surface. Resuspension Factor Approach The resuspension factor, K, is defined as the ratio of air activity/m> divided by the surface activity/m°, and thus has units of m, Mishima” have tabulated values of K from many experiments. is from 107° to 10743/m. Stewart? and The total range Most of the high values, however, are derived from experiments with laboratory floor surfaces and with artifical disturbance. For outdoor situations Stewart! suggests a value of 107°fn "under quiescent conditions, or after administrative control has been established in the case of an accident.” A value of 10°?/m is suggested under conditions of moderate activity. After reviewing the literature, Kathren> recommended the use of 107" fn as a@ conservative velue. These values, however, address the situation following a fresh deposit of activity. Several studies have demonstrated that the amount of material moving in resuspension decreases with time following its initial deposition’? ?, Observed half-times of this decrease are 35 to 7O days. The mechanism causing this decrease is apparently the weathering of the surface deposited debris into the soil, and not the loss of the deposited material from the initial 2 area. Kathren's model? includes this effect by multiplying his chosen camp Mey grrypemesconet yen we ee ro ge ee Omer . tt, 1 1 . “. wr 5 ma bs