Quotas work at user level not folder level so that is a bit of a red herring I'm affraid.
On the other hand you could create logical drives for each of the 10 depts on an extended partition or several extended partions depending on your disc setup )- the partition size being the 'quota' for each dept. As long as you can make some space free to do the necessary file shuffling to get this working it could well be a viable solution.
Maintenance of such a system is a bit trickier than normal quota management but it shouldnt be too bad. Typically to increase a quota you'd back up the data, delete its logical drive and recreate the drive with a larger size and restore the data. Bearing this in mind plan ahead for the quota size requirements.
Not the ideal solution, but its a valid workaround giving you the desired results at the 'cost' of the quotas being rather rigid.