Bases for secondary standards for residual radionuclides in soil and some recommendations for cost-effective...

The future use of land contaminated with radionuclides depends upon scientifically defensible bases for setting limits for radionuclides in soil. The purpose of this work is to develop such bases for establishing "posting criteria" to protect nonradiological workers at the Nevada Test Site and to provide a rationale for cost-effective measurements to readily determine the boundary conditions. The analysis begins with a mandated limit on total effective dose equivalent (1 mSv y(-1)) via all pathways. The possible pathways of exposure are external gamma exposure, inhalation of resuspended material, and incidental soil ingestion. These pathways are evaluated for each radionuclide of interest on the Nevada Test Site, and the results are used to define for each radionuclide the deposition-density limits for each pathway of exposure. The minimum deposition-density limits are noted to occur via the external gamma-exposure pathway for most radionuclides; exceptions are incidental soil ingestion for 90Sr/90Y and inhalation for 238Pu, 239,240Pu, and 241Am. The limiting values of deposition density or average concentration in soil are then determined appropriately by combining all pathways. Procedures are developed for dealing with mixtures of many radionuclides and to apply the principles developed so that even a simple measurement of external gamma-exposure rate may be used to define the boundary conditions in the field, provided that the relative abundance of the radionuclide mixture is known and that the defining level of exposure rate is sufficiently above background.