Health Physics Questions and Answers - Question 201

Question 201: Why is it that releases to sanitary sewers are not included in the dose limit for members of the public while other effluent releases are?

Answer: The practice of having separate limits for discharge to sewers is a practice that has been in place since 10 CFR Part 20 was proposed in 1955. If the dose limit for individual members of the public included the dose contribution of licensed material into sanitary sewerage, there would be no practical way for the licensee to determine the magnitude of that dose contribution for the purpose of demonstrating compliance with the limit because of the remoteness of the individual being exposed from the point of discharge. Water released into the sanitary sewer is considered unavailable until it passes through the sewage treatment plant. Effluent concentration limits (as in Table 2 of Appendix B) have always been calculated under the premise that a member of the public lives at the licensee's site boundary and utilizes the air and water available at that point. Release limits are set in Table 3 so that if the releases from the sewage treatment facility were the only source of ingestible water, the dose to the individual would be a committed effective dose equivalent of 0.5 rem per year.

(Reference: 10 CFR 20.1301)