Step 1
Go to the Properties Module > List View.
Step 2
Leave the Title box blank but select the Department you want to clean up the properties for (1). Click the Apply and Refresh button (2).
Step 3
Sort the results by the "Sub. In" column. (Sort it so the black triangle indicator is pointing up. this puts the older projects at the top of the list)
Step 4
Select then R-Click (Control Click) on a property. (You can select multiple Properties at one time to archive; However the more properties you have selected the longer the archiving process will take. 10 properties at a time is a good amount.) Select Archive from the Pop-up menu.