Hi, Ron,
If you want to stop UM from sending alerts about this specific volume, you have two ways of doing it in UM7.2:
1. Configuration\Alerts. Take the volume offline alert from the list you have already configured. This way, UM may still generate an event for it, but you will not receive an alert.
2. Configuration\Manage Events. You can also disable this particular event for this volume here, so the event will not be generated at all.
Julia