From 1998 to 2000, through the Interagency Steering Committee on Radiation Standards (ISCORS), the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Environmental Protection Agency (EPA) conducted a joint survey (hereafter referred to as the ISCORS sewer survey) to collect information on radioactivity in sewage sludge and ash from sewage treatment plants referred to in the industry as publicly owned treatment works (POTWs). The objectives of the survey were to (1) obtain national estimates of high-probability occurrences of elevated levels of radioactive materials in sludge and ash at POTWs, (2) estimate how much radioactive contamination comes from NRC and Agreement State licensees and how much from naturally occurring radioactivity, and (3) support rulemaking decisions by NRC and EPA.