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)