BATTELLE Rudolf J. Engelmann NORTHWEST —~3- March 12, 1971 Resuspension factors would more correctiy model the physics of the resuspension if we were to add the qualification that we were interested only in the immediate inhalation hazard. If we are also interested in the long-term translocation of the source and subsequent resuspension to an inhalation hazard, we must also now define a resuspension factor for particle saltation and surface creep. These are the processes which move greater than 50 to 100 um diameter particles. The early work of R. A. Bagnold and W. S. Chepil on soil movement has shown that 90% of the airborne material is within one foot of the surface and that obviously the airborne soil diameter decreases with an increase in height. Consequently the resuspension factor would increase if the airborne concentration were measured closer to the surface. Thus, a resuspension factor for tracer movement by saltation may be several orders of magnitude greater than the 6 x 1072 to 1077 m7l for the inhalation hazard. We recommend that data be obtained to determine the saltation resuspension factor. Data are also needed to establish how the tracer is moved--is the tracer resuspended by itself or is the tracer attached to the host soil particle? This attachment would probably be more important for smaller sized particles. A modeling problem using the resuspension factor exists in evaluating the boundary conditions if any of the tracer moves in either surface creep or in saltation. These cases are not considered in existing particle diffusion models. We will suggest the nature of the problem. Particles moving in saltation initially acquire suffi- cient energy to cause the particle to move almost vertically upward. Depending upon the amount of energy imparted, the particles will rise to various heights before the particle motion can be assumed to be de- _% scribed by a Sutton type diffusion model.