I fixed this by limiting the amount of files that Enterprise Logging sotes by adding the following to app.config within the listener declaration:
maxArchivedFiles="20"
Now the logging will only keep up to 20 files and delete the oldest as this threshold is reached.
Another way I found to do this which does not involve Enterprise Library can be found here: Background Worker Check For When It's Midnight?
This done through System.IO to raise an event when a certain time has elapsed. It is then combined with a function to delete all files as found in this answer: