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Naturally-Occurring Radiation: 

Joint NRC/EPA Sewage Sludge Radiological Survey

TENORM Sludge Report
Survey Design and Test Site Results
B. Background

Federal Regulations

Specific amounts and concentrations of radioactive material are legally authorized to be disposed into the sanitary sewage collection system by Federal and State regulations. In 1991, NRC revised its sewer disposal criteria, partially in response to evidence that certain radioactive materials were reconcentrating in sewage sludge or incinerator ash. The revised NRC regulations further limited the radioactive materials that NRC licensees are allowed to discharge to POTWs, which should preclude contamination at POTWs. The current NRC regulations in 10 CFR 20.2003 permit disposal of specific quantities of soluble material into a sanitary sewer. NRC plans to use the survey information in assessing whether to apply further restrictions to the licensed radioactive material that is being discharged to sanitary sewage collection systems.

The EPA standard for the use and disposal of sewage sludge (biosolids) in 40 CFR Part 503 does not include limits for radioactive material. POTW operators have requested that EPA regulations address radioactive materials so POTWs would have a basis to restrict discharges of radioactive materials to the sewage collection system. EPA plans to use the survey results to evaluate the need to include limits on radioactive materials in biosolids standards.

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Sources of Radioactive Materials

One possible source of radioactive material entering a POTW involves naturally-occurring sources such as groundwater, which can contain elevated levels of radioactive materials in some parts of the U.S., as well as drinking water treatment residuals disposed of into the sanitary sewage collection system. Another possible source is the authorized disposal by users of radioactive materials (such as NRC and Agreement State licensees) of man-made radioactive materials into the sanitary sewage collection system. The removal of contaminants by various methods at POTWs, and the reduction of the volume of solids that contains these contaminants (e.g. incineration of sludge), can cause reconcentration of radioactive materials in the treatment facility's sewage sludge or ash.

Background information on the nature of radioactivity in sewage sludge can be found in reports published by NRC in 1992 and 1994 entitled "Evaluation of Exposure Pathways to Man From Disposal of Radioactive Materials Into Sanitary Sewer Systems" (NUREG/CR-5814) and "Reconcentration of Radioactive Material Released to Sanitary Sewers in Accordance with 10 CFR 20" (NUREG/CR-6289), respectively. Another useful background document is a report entitled "Radioactivity of Municipal Sludge" issued by EPA during the development of the first round rulemaking of the 40 CFR Part 503 sewage sludge technical rule.

Congressional Interest

This survey responds, in part, to a recommendation in the General Accounting Office (GAO) report, "Actions Needed to Control Radioactive Contamination at Sewage Treatment Plants," published in May 1994. The GAO report recommended that NRC determine the extent of elevated levels of radioactive materials at POTWs and establish acceptable limits for radioactive materials in sewage sludge and ash.

A joint House/Senate hearing was held in 1994 to officially release and address questions raised in the GAO report. The hearing was stimulated by concerns associated with elevated levels of radioactive materials in incinerator ash at a major sewage treatment plant in the Cleveland, Ohio, area. The GAO stated that, over the past 20 years, NRC documented about a dozen situations where elevated levels of radioactive materials were identified in sewage sludge or sludge incinerator ash; but, there has been no national survey of radiation levels present in sewage sludge or sludge incinerator ash to determine if this is a widespread problem.

At the time of the hearing, EPA was planning to conduct a second National Sewage Sludge Survey (NSSS) to support its efforts to develop the second round of the 40 CFR Part 503 sewage sludge technical regulations. EPA's planned survey would have included the collection of data on concentrations of radioactive materials in a representative sampling of POTW sludges from across the country. (The first national survey conducted in the late 1980s did not include analysis of radioactive material.)

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Testimony presented by both NRC and EPA during the 1994 hearing noted that there was no indication of a widespread problem in this area and the Cleveland incident appeared to be an isolated incident. Based on limited information on radiation levels in sewage sludge and ash across the country, it appeared that reconcentration of radioactive materials may have been associated with authorized insoluble industrial releases from both NRC and Agreement State licensees, which was documented and used as a basis of the GAO report. These problems occurred prior to the revision to NRC’s regulations in 1991.

Industry Interest

In 1996, the Association of Metropolitan Sewerage Agencies (AMSA) conducted a confidential voluntary survey of concentrations of radioactive materials in some of its members' POTW sewage sludges and ashes. The objective was to develop a better estimate of the concentration of radioactive materials in sewage sludges and sludge incinerator ashes. Samples from 55 wastewater plants in 17 States were supplied voluntarily and analyzed for radioactive materials. These plants were distributed across the country and ranged in size from small to among the largest POTWs. The most significant levels of radioactive material were the potassium and radium isotopes, which are naturally-occurring radioactive materials. The restricted nature of the AMSA survey limited its usefulness in assessing regional background levels of radioactive materials or the effects of licensees that dispose of radioactive material into sanitary sewers.

Current Plans

EPA is not currently planning to move forward with a second NSSS. Based on EPA’s plans and the limitations of the AMSA survey, NRC and EPA decided to jointly fund a survey of POTW sewage sludges and ash to assess the potential need for NRC and/or EPA rulemaking. The survey information will also be referenced in a joint NRC/EPA guidance document for POTWs, which is currently under development by the ISCORS Sewage Subcommittee. This guidance would provide information to help POTW operators determine sources of radioactive materials at POTWs, describe sampling and analysis procedures, and advise whether a response is needed to the presence of radioactive material in sludge.

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