The ISCORS Multimedia Radiological Dose Assessment of Municipal Sewage Sludge and Ash. W. A. Chiu, J. T. Bachmaier, R. K. Bastian, R. T. Hogan, and T. Lenhart; US Environmental Protection Agency, DC, US Department of Energy, US Nuclear Regulatory Commission, Northeast Ohio Regional Sewer District
Managing municipal wastewater at publicly owned treatment works (POTWs)leads to the production of considerable amounts of residual material, known as sewage sludge or biosolids. If the wastewater entering a POTW contains radioactive material, then wastewater treatment and sludge management processes may concentrate radionuclides in sewage sludge or incinerator ash, leading to possible exposure of the general public or POTW workers. The Sewage Sludge Subcommittee of the Interagency Steering Committee on Radiation Standards (ISCORS), which consists of representatives from the Environmental Protection Agency, the Nuclear Regulatory Commission, the Department of Energy, and several other federal, state, and local agencies, is developing guidance for POTWs on the management of sewage sludge that may contain radioactive materials. As part of this effort, the ISCORS Subcommittee conducted a radiological dose assessment to evaluate the potential risk to human health posed by radionuclides in sewage sludge and ash. Because the assessment needed to have general applicability across a wide range of conditions, the basic approach was to model sites in a generic manner using relatively simple conceptual models while incorporating uncertainty and variability by a variety of methods. A number of scenarios were developed to depict typical exposure situations. The RESidual RADioactivity (RESRAD) family of probabilistic computer codes was used to calculate dose-to-source ratios (total effective dose equivalent per unit of radioactivity in sewage sludge) for each radionuclide of concern for each exposure scenario. Potential radiation doses were then estimated using results of a radioanalytic survey of radioactivity in sewage sludge and ash conducted jointly by EPA and NRC.
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