Federal Guidance Report #12, External Exposure to Radionuclides in Air, Water, and Soil, EPA 402-R-93-081; and Report #11, Limiting Values of Radionuclide Intake and Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion (whew!), EPA-520/1-88-020 may be of help. Chris Alston