We allow any staff member (nearly 7,000 staff) to sign up for a wordpress site on our server. We host around 1500 sites currently although I know that a large percentage of them were created out of curiosity, as part of a training that was never utilized or belongs to a person who is no longer employed with us. I would like to have a way to periodically clean out old sites (say, sites that have not been edited in past year). Any ideas on how I might accomplish this?