REVIEW OF RESUSPENSION MODELS 227 



Thus the air concentration of the contaminant is given by the product of the 

 concentration of the contaminant in the soil and the concentration of the soil particulates 

 in the air. If the quantity of particulates in the air is known from other data, one need, 

 theoretically, only measure the soils in the region to provide an estimate of the air 

 concentration of the contaminant. 



Two parameters, the dust loading in the atmosphere and the appropriate concentra- 

 tion of the contaiTiinant in the soil, are needed to provide estimates by this method. 

 Healy (1974) used an average value of 120 jUg/m^ of dust in a generic analysis of limits 

 for plutonium in the soil. Tliis was derived from the Federal Secondary Standard for 

 particulates in the air expressed as a geometric mean of 60 A^g/m^ assuming a geometric 

 standard deviation of 2. Anspaugh (1974) explored a reasonable mass loading in several 

 ways. Tlie lower bound is quoted as about 10 i^g/m^ . Examination of the data on the 

 levels in mine atmospheres which have led to a considerable prevalence of pneumoco- 

 niosis in the workers indicates that standards on the range of 1 to 10 mg/m^ have a very 

 small, if any, margin of safety. Anspaugh (1974) also quotes some British data which 

 indicate that dust levels in excess of 1 mg/m^ could lead to considerable public health 

 problems. He also used the data on ambient mass loading for 1966 from the National Air 

 Surveillance Network to show that the average for urban stations ranged from 33 to 254 

 jUg/m^ with a mean for all nonurban locations of 38 idg/m^ . For the nonurban stations 

 the average ranged from 9 to 79 idg/m^ . From these studies he chose an average of 100 

 jUg/m^ as reasonable for predictive purposes (Anspaugh, Sliinn, and Wilson, 1974; 

 Anspaugh et al., 1975). The U.S. Environmental Protection Agency (1977) also 

 examined the data from the nonurban stations from the National Air Surveillance 

 Network for the years of 1964 and 1965. Their map of these data indicates values ranging 

 from 9 iUg/m^ in southern Montana to 56 /Ug/m^ in western Pennsylvania, 57 Mg/m^ on 

 the southern Oregon coast, and 59 lug/m^ on the North Carolina coast. However, the 

 prevalence of high values in the east would indicate the possible inclusion of industrial 

 particulates in these samples. The U. S. Environmental Protection Agency used a value of 

 100 jUg/m^ in the calculation of their screening level. 



Several uncertainties appear in the use of the data from the National Air Surveillance 

 Network. The first was pointed out above in that the particulates that are collected can 

 include a portion of those generated by industrial operations; so the values could be high. 

 The second problem arises from the fact that the samplers are frequently in positions, 

 such as on top of buildings; so they do not measure the air actually breathed by people. 

 Associated with this question is the potential for people engaged in various activities to 

 generate their own dust. Tliis would result in local concentrations in excess of the 

 ambient value measured by the network. However, the 100 /ig/m^ value still appears 

 reasonable from the standpoint that it is an average over a full year, and people do not 

 work or play in dusty operations all the time. For example, if we assume that an 

 individual spends 8 hr per day, 5 days per week, 50 weeks per year in a concentration five 

 times the maximum value noted in the ambient air measurements, or 300 jug/m^ , the 

 average concentration through the year would be only 115 )Ug/m^ . Although some 

 individuals, such as farmers, work longer hours during the week, their exposure to dust is 

 limited to fewer weeks per year, and a portion of their time in the field is during periods 

 of high moisture or vegetation in the soil when dusty conditions are limited. 



Associated with the question of the concentration of soil particles in the air is the 

 question of the origin of the particles. Once airborne, the smaller particles can travel very 



