Squid does not release disk space

I’ve configured a squid service, giving it 2.5 GB of HDD space in a separated partition.
My squid.conf file includes the following line:
cache_dir ufs /usr/squid/cache 256 16 256
But, after some time of use, squid reports that its allocated space is over the quota and the only way to correct the problem is increasing the quota or erasing the contents of the cache dir.
My question is:
Is there a way to configure squid to auto release the space that has not being used in tha last X days?