Applicable state and federal laws largely determine the disposability
of media, as previously explored in threads such as
http://www.mail-archive.com/adsm-l AT vm.marist DOT edu/msg74957.html

If media is kept in a secured facility, then the issue is moot, as no
unauthorized persons will gain access to the media.  Under such
circumstances there is no issue as to rewriting or data
recoverability at any point.

   Richard Sims