Assessment of risk from land application of waste water containing elevated levels of naturally occurring radioactive materials

摘要

On-site land application of waste watercontaining very low levels of site-derived contaminantsis a commonly used method of disposal. However, theresidual soil contamination resulting from suchpractices may complicate and increase the costs of siteremediation if constituent soil concentrations exceedregulatory clean-up standards. The long-term potentialhuman health impacts of land application of wastewater containing elevated levels of naturally occurringradionuclides for a hypothetical in-situ uraniumfacility were investigated using the U. S. Department ofEnergy RESRAD Computer Code for assessment ofdose and risk. The post-reclamation radiation doses inexcess of background, attributable to land applicationof waste water containing uranium and its decayproducts thorium and radium, were calculated forseveral different conditions assuming rural-residentialuse of the land. For contaminated land areas of 10acres or more, the estimated doses were directlyproportional to the soil radionuclide concentrationwhen the thickness of the contaminated soil andhydrological parameters were held constant. Themaximum annual radiation dose to a rural resident onland with surface soil concentration equal to 295 pCi/gnatural uranium was estimated to be 34 mrem. Incontrast, the maximum annual radiation dose to thishypothetical individual from ~(226)Ra at the residualconcentration allowed under the regulations foruranium mill tailings, i.e., 5 pCi/g, varied from 135mrem to 283 mrem depending on the thickness of the contaminated layer.