Decay Storage Requirements

[William Lorenzen <LORENZEN_W@A1.TCH.HARVARD.EDU>]

What is the scientific/technical basis for the regulatory requirement of holding 
radioactive wastes for a minimum of 10 half-lives prior to release.  Is there a 
technical reference as to why it is not 7 or even 12 for that matter.  The 
requirement is always accompanied by the need to survey with conventional 
instrumentation.... prior to release. For low activity wastes the 10 half-lives 
+ surveys can be overkill. 

If a researcher uses radioactivity for an experiment and does a survey of 
his/her experiment wastes at the bench top and finds no detectable radioactivity 
on the materials they are not placed in the radioactive waste.  So if one was to 
survey wastes which are held for decay after 5 or even 7 half-lives and finds no 
detectable activity why can't it be released?

Any technical basis for this requirement would be helpful.