Water and wastes which have been discharged from residences and businesses into a municipal sewers are treated at wastewater treatment plants. The discharged water and wastes may contain both man-made and naturally occurring radionuclidesradionuclideRadioactive forms of elements are called radionuclides. Radium-226, Cesium-137, and Strontium-90 are examples of radionuclides. which can accumulate in the treatment plant, its sludges, and solid wastes.

Study of Wastewater Treatment Plant TENORM

A multi-year study conducted by EPA and other federal agencies who are members of the Interagency Steering Committee on Radiation Standards (ISCORS) Exit provided detailed information on radionuclides in publicly-owned wastewater (sewage) treatment plants. They initially conducted a Pilot Survey, which was followed by a nationwide survey.

Sewage Sludge Pilot Publicly-Owned Treatment Works (POTW) Survey

ISCORS established a subcommittee to examine radiation found in sewage sludge and the ash from its incineration. The sources of radiation may be Nuclear Regulatory Commission (NRC) licensees, industrial discharges and technologically enhanced naturally occurring radioactive material (TENORM). The Subcommittee's first project on the issue was a pilot survey on the production of radioactively contaminated wastes at nine Publicly-Owned Treatment Works (POTWs):

Joint NRC/EPA Sewage Sludge Radiological Survey: Survey Design & Test Site Results
This report contains the results of a radiological survey of nine publicly POTWs around the country, which was commissioned by the Sewage Sludge Subcommittee, to determine whether and to what extent radionuclides concentrate in sewage treatment wastes.

Sewage Sludge National Survey

Following completion of the pilot study, ISCORS undertook a nationwide survey, obtaining sludge and ash samples from more than 300 POTWs. Three reports based on this work are available:

ISCORS Assessment of Radioactivity in Sewage Sludge: Radiological Survey Results and Analysis
This final report presents survey results and analyses by EPA and the NRC of radionuclides in sludge and ash samples from the POTWs in the survey.

ISCORS Assessment of Radioactivity in Sewage Sludge: Modeling to Assess Radiation Doses
This final report, which underwent peer review and public comment, looks at the potential transport of radioactivity from sludge into the local environment. It describes the radiation pathway modeling, actual results of radioactivity found in sewage sludge samples, and tracks potential transport under a number of hypothetical scenarios. NRC and EPA used this approach to help interpret the results of the survey. For each scenario, they assessed the potential levels of radiation exposure and dose to both POTW workers and the public.

ISCORS Assessment of Radioactivity in Sewage Sludge: Recommendations on Management of Radioactive Materials in Sewage Sludge and Ash at Publicly Owned Treatment Works
This final report, which underwent public comment, makes recommendations to POTW operators on determining whether radioactive materials in sludge or ash, including TENORM and radon, could threaten the health and safety of POTW workers or the general public. From its survey results, ISCORS concludes that radiation levels in sewage sludge and ash at most POTWs do not present an exposure concern to workers or to the general public. They also conclude that the radiation levels are low enough that sludge and ash continue to be safe soil amendments for growing food crops.

Note: These reports predated the practice of discharging the waste from unconventional shale oil and gas development, which led to increases in volumes and concentration of radioactivity being discharged to these POTWs. In 2016, EPA adopted new pre-treatment standards for this industrial sector.