Since you're only concerned with the traffic transiting the T1, here's what I would suggest:
There are a number of different ways to accomplish this but maybe the easiest thing to do is to install PRTG (assuming you're running some version of Windows) on your workstation. In PRTG set up a packet sniffing sensor. On the switch that your ASA connects to set up a port monitor to mirror traffic on the ASA switch port to the port that the PRTG computer is running on. This will show you not only the total volume of traffic transiting the ASA switch port (to and from the internet via the T1), but will also show you the volume of traffic based on protocol, source, and destination. If you don't know how to set up a port monitor or if your switch doesn't support port monitoring, you can plug a hub in between the ASA and the switch and plug your PRTG machine in to the same hub in order to see all of the traffic transiting the ASA.
Some additional info based on your comment to my answer:
If you don't have a managed switch then you'll have to use a hub (or you can purchase a cheap managed switch that supports port monitoring and use it instead of a hub).
I'll try not to over complicate this. If you have a hub then do this: Unplug the network cable going from the switch to the ASA and plug it in between the switch and the hub. Then using another network cable, plug it in between the hub and the ASA. Basically you're inserting the hub between the switch and the ASA. Then plug your PRTG computer into the hub. Because a hub floods traffic to every port, all the traffic going between the switch and the ASA will be seen by PRTG running on the workstation. So here's a little diagram of what you need to set up:
The <---> and <---^ lines are network connections (cables).