Hi David. I was struggling with a similar problem this week. We had accumulated over 40 GB over time. In my case, restarting did not help, but i noticed that all the space was taken by temporary folders inside the standalone dir. If you look up docs on JBoss folder structure, you will see that three of your folders are created by JBoss after the first run for storing temporary data related to deployments. Those are named log, tmp, and data. Most of the 40 GB where inside the data folder. You cannot just delete those folders if applications are deployed because JBoss will then complain that your deployments are missing their data, but if you undeploy all of your own apps, delete the three folders, and redeploy, you are all good.
Now I know, that this is not an automated solution but I will say that in my apps case it has taken many months to reach 40 GB, so until I find a better solution I will just stop redeploying constantly and instead, undeploy, delete the folders manually, and then redeploy. Know that if you find a better way or hear more about this I am all ears.